Multi-paradigm: object-oriented (class-based), structured, imperative, generic, reflective, concurrent

Typing discipline:

Static

compile time

strong

stricter typing rules at compile time

safe

do not allow operations or conversions that violate the rules of the type system.

nominative [ˈnɒmɪnətɪv]

compatibility and equivalence of data types is determined by explicit declarations and/or name of the type.

manifest

explicit identification of each type in code.

• Simple: Java is easy to learn. The syntax of Java is based on C++.
• Object-Oriented.
• Portable: Java supports read-once-write-anywhere approach. bytecode (.class)
• Platform Independent: Java doesn't depend upon the operating system to be executed.
• Secured: Java is secured because it doesn't use explicit pointers. Java also provides the concept of ByteCode and Exception handling which makes it more secured.
• Robust: Java is a strong programming language as it uses strong memory management. The concepts like Automatic garbage collection, Exception handling, etc. make it more robust.
• Architecture Neutral: architecture (32 bit or 64 bit) which doesn't exist in Java.
• Interpreted: Java uses the Just-in-time (JIT) interpreter along with the compiler for the program execution.
• bytecode is "close" to native code. It is still a little bit slower than a compiled language (e.g., C++).
• Multithreaded:
• Distributed: Java is distributed because it facilitates users to create distributed applications in Java. RMI and EJB are used for creating distributed applications. This feature of Java makes us able to access files by calling the methods from any machine on the internet.
• Dynamic: Java is a dynamic language. It supports dynamic loading of classes. It means classes are loaded on demand. It also supports functions from its native languages, i.e., C and C++.

• 1996 Java 1.0: Dictionary, Vector, Stack, and Properties before Collections
• 1998 J2SE 1.2 and j2ee and j2me: Collections Framework
• SE 4 "assert"
• 2004 SE 5 high-level concurrency features. java.util.concurrent, Iterator, for-each, enum,generics, autoboxing
• 2006 SE 6 rename ti Java EE, Java ME and Java SE, NavigableMap, @Override in interface
• SE 7 - diamonds, ARM, multi-catch, try-with-resources, fork/join framework.
• 2014 SE 8 lambda, type annotation
• SE 9 Modules, private methods in interfaces
• SE 10 Local variable type interface

JVM is an acronym for Java Virtual Machine; it is an abstract machine which provides the runtime environment in which Java bytecode can be executed. It is a specification which specifies the working of Java Virtual Machine. Its implementation has been provided by Oracle and other companies. Its implementation is known as JRE.

It is a runtime instance which is created when we run the Java class. There are three notions of the JVM: specification, implementation, and instance.

JRE stands for Java Runtime Environment. It is the implementation of JVM. The Java Runtime Environment is a set of software tools which are used for developing Java applications. It is used to provide the runtime environment. It is the implementation of JVM. It physically exists. It contains a set of libraries + other files that JVM uses at runtime .

JDK is an acronym for Java Development Kit. It is a software development environment which is used to develop Java applications and applets. It physically exists. It contains JRE + development tools. JDK is an implementation of any one of the below given Java Platforms released by Oracle Corporation:

Зачем?

1. необходимость преодоления границ операционных сред;
2. устранение разнородности объектных моделей, вызванных тем, что классы и объекты, построенные в различных инструментальных средах, имеют определённые отличия.

Распределённые объектные архитектуры (CORBA, DCOM, Java RMI, WEB-services), обладая многими перечисленными свойствами, имеют следующие недостатки:

1. необходимость перекомпиляции программных кодов при внесении изменений в объекты и интерфейсы;
2. невозможность динамической адаптации поведения программных объектов в зависимости от состояний и поведения среды;
3. невозможность работы в явной форме с моделями знаний;

AOP has externally specified agents (with interfaces and messaging capabilities) at its core. They can be thought of as abstractions of objects. Exchanged messages are interpreted by receiving "agents", in a way specific to its class of agents.

Агентом является всё, что может рассматриваться как воспринимающее свою среду с помощью датчиков и воздействующее на эту среду с помощью исполнительных механизмов.

JADE framework (основана на Java RMI, Java CORBA IDL, Java Serialization и Java Reflection API) придаёт Java агентам следующие свойства:

https://www.oracle.com/technetwork/java/catalog-137601.html

database

[ˈdeɪtəˌbeɪs] is an organized collection of data

database management system (DBMS)

app that interacts with end users, other applications, and the database itself

Ссы́лочная це́лостность (англ. referential integrity)

[ˌrɛfəˈrɛnʃəl] необходимое качество реляционной базы данных, заключающееся в отсутствии в любом её отношении внешних ключей, ссылающихся на несуществующие кортежи.

Relational databases - most use SQL [rɪˈleɪʃənəl]. NoSQL - any other. (Object-relational database ORD and object database management systems)

Common logical data models for databases:

Navigational databases

Graph database, Network model, Hierarchical database model

(no term)

Relational model

Entity–relationship model

Enhanced entity–relationship model

Object model

object-oriented

Document model

subclass of key-value storage noSQL, XML databases,

Entity–attribute–value model

object–attribute–value model, vertical database model, and open schema. InfinityDB

(no term)

Star schema

Таблица из foreign keys - junction table (or "link table") - many-to-many

• Stored procedure - subroutine available to applications that access a RDBMS

Детерминированность системы - отсутствие рандомов.

1. equals(String str)
   • value
   • Objects.equals() checks for null before calling .equals() so you don't have to (available as of JDK7, also available in Guava).
   • equalsIgnoreCase() - case-insensitive
2. compareTo(String anotherString), compareToIgnoreCase(String str)
   • lexicographically
   • used for orderding string in a list
   • compare() - by their length
3. == by reference
4. String.contentEquals() compares the content of the String with the content of any CharSequence (available since Java 1.5)

[ˈɪntɜːn] Special storage area in Java heap

String object in the string constant pool is called as String Intern

intern() - Create an exact copy of heap memory string object in string constant pool.

"" = pool new or result of method = string object

heap memory StringBuffer - if you need thread safety

StringBuffer sb = new StringBuffer("JAVA");
sb.append("J2EE");

StringBuilder - if you dont need.

StringBuilder sb1 = new StringBuilder("JAVA");
sb1.append("J2EE");

string in string pool stored until unless garbage collected. It’s a security risk because anyone having access to memory dump can find the password as clear text. If we use char array to store password, we can set it to blank once we are done with it.

• https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html
• https://docs.oracle.com/javase/8/docs/api/java/util/regex/Matcher.html

PatternSyntaxException object is an unchecked exception that indicates a syntax error in a regular expression pattern.

import java.util.regex.Pattern;
import java.util.regex.Matcher;

String nazn = "за 31/01/2018 никулкин владимир иванович г.барнаул ул.георгия "
                +"исакова,169-17 оплата по сч ак-2083 от 29,01,2018 вознаграждение агента за газ 2705,в т.ч.ндс 1525,42 руб";

        Pattern p = Pattern.compile("[^а-яА-ЯёЁ/-//\\s]");

        Matcher m = p.matcher(nazn);

        String[] arr = m.replaceAll("").split("\\s+");

        System.out.println(Arrays.toString(arr)); Pattern p = Pattern.compile(REGEX);

Pair with comarator:

public class Util {
    public static <K, V> boolean compare(Pair<K, V> p1, Pair<K, V> p2) {
        return p1.getKey().equals(p2.getKey()) &&
               p1.getValue().equals(p2.getValue());
    }
}

public class Pair<K, V> {

    private K key;
    private V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public void setKey(K key) { this.key = key; }
    public void setValue(V value) { this.value = value; }
    public K getKey()   { return key; }
    public V getValue() { return value; }
}
Pair<Integer, String> p1 = new Pair<>(1, "apple");
Pair<Integer, String> p2 = new Pair<>(2, "pear");
boolean same = Util.compare(p1, p2);
//OR
boolean same = Util.<Integer, String>compare(p1, p2);

<U extemds Number> - upper bound

Wildcards - ?

• List<? extends Number> - upper bounded ?
• List<? super Integer> - lower bounded ?
• List<?> - unbounded wildcards when we do not depend on type parameter.

Windcard Guidelines copy(src, dest) == copy(in, out)

in varible

upper bound - extends

out

lower bound - super

(no term)

In the case where the "in" variable can be accessed using methods defined in the Object class, use an unbounded wildcard.

(no term)

code need to access the varible both "in" and "out" - do not use a wildcard.

(no term)

Using a wildcard as a return type should be avoided.

• Cannot Instantiate Generic Types with Primitive Types
• Cannot Create Instances of Type Parameters
• Cannot Declare Static Fields Whose Types are Type Parameters
• Cannot Use Casts or instanceof With Parameterized Types
• Cannot Create Arrays of Parameterized Types
• Cannot Create, Catch, or Throw Objects of Parameterized Types
• Cannot Overload a Method Where the Formal Parameter Types of Each Overload Erase to the Same Raw Type

побитовые и сдвиговые

• invert or flip ~
• signed shift << >> - added bit depends on sign.
• unsigned shift >>> <<< - add 0 always
• & AND
• | inclusive OR
• ^ exclusive OR (XOR) 1 1 = 0

Negative values - two's complement. Negative numbers are representing by negating (flipping) all the bits and then adding 1. Still, if the leftmost bit is 0, the number is positive. Otherwise, it is negative.

>> division by 2^n. Or division by 2^n -1 in case of odd numbers (нечетных)x

[ˈprɛsɪdəns] = right to left, others left to right.

1. unary
2. multiplicative * / %
3. additive + -
4. shift
5. relational [rɪˈleɪʃənəl] < > <= >= instanceof
6. equality = !
7. bitwise: (in Preecedence) & ^ | && ||
8. &&
9. ||
10. ?:
11. assignment = += *=

if you are a package developer, you might have to create your own set of exception classes to allow users to differentiate an error that can occur in your package from errors that occur in the Java platform or other packages.

IF yes for one of questions:

• Do you need an exception type that isn't represented by those in the Java platform?
• Would it help users if they could differentiate your exceptions from those thrown by classes written by other vendors
• Does your code throw more than one related exception?
• If you use someone else's exceptions, will users have access to those exceptions? A similar question is, should your package be independent and self-contained?

Good practice to append the string Exception to the names of all classes that inherit (directly or indirectly) from the Exception class.(e.g LinkedListException)

Errors are normally used for serious, hard errors in the system, such as those that prevent the JVM from running.

Numbers => locale-sensitive String. 123456.78 => 123 456,78 in France: 123.456,78 in Germany

JSR 354 – “Currency and Money”

java.text.NumberFormat

  Integer quantity = new Integer(123456);
    Double amount = new Double(345987.246);
    NumberFormat numberFormatter = NumberFormat.getNumberInstance(currentLocale);
    String quantityOut = numberFormatter.format(quantity);
    String amountOut = numberFormatter.format(amount);
    System.out.println(quantityOut + "   " + currentLocale.toString());
    System.out.println(amountOut + "   " + currentLocale.toString());
 NumberFormat currencyFormatter =
        NumberFormat.getCurrencyInstance(currentLocale)

System.out.println(currencyFormatter.format(currencyAmount) );

123 456 fr_FR 345 987,246 fr_FR 123.456 de_DE 345.987,246 de_DE 123,456 en_US 345,987.246 en_US

9 876 543,21 € - france 9.876.543,21 € - germany $9,876,543.21 - US Dollar

Неправильный результат в частных ситуациях:

i=(int )(n+0.5); // классическое округление
i=(int )(n+1); //округление до большего целого
i=(int )(n);// округление до меньшего целого

• Math.round() - до ближайшего целого. 0 < 0,5 или 0 >=0,5 = HALF_UP - default!
• Math.floor() - до нижнего целого
• Math.ceil() - до верхнего целого

BigDecimal c1 = a1.divide(b1, 9, BigDecimal.ROUND_HALF_UP); => 0.666666667

HALF_EVEN - 3,5 = 4 ; 4,5 = 4

Double 0.1 + 0.2 - 0.3=5.551115123125783E-17 (becouse of .toString()

Gaussian- , or bankers' rounding(для копеек и рублей)(по правилам арифметики): 0.5->1

double result = 0.1 + 0.2 - 0.3;
BigDecimal resultRounded = new BigDecimal(result).setScale(2, BigDecimal.ROUND_HALF_UP);
System.out.println("0.1 + 0.2 - 0.3=" + resultRounded);

=> 0.1 + 0.2 - 0.3=0.00

When doing complex financial simulations, you don't want to round at all.

https://docs.oracle.com/javase/7/docs/api/java/math/RoundingMode.html

String to Date and Date to String:

private static SimpleDateFormat ft = new SimpleDateFormat ("yyyy-MM-dd");
Date d;
try {
        d = ft.parse(rs.getString("birthday"));
        String ds = ft.format(d);
} catch (ParseException e) {
        System.out.println("Unparseable using " + ft);
}

• LocalDate - birthday
• LocalTime - nanosecond precision
• LocalDateTime
• ZonedDateTime - it is recommended to use a simpler class without a time-zone. The widespread use of time-zones tends to add considerable complexity to an application.

LocalDate.parse("2007-12-03") //year month day

AnonymousInner an_inner = new AnonymousInner() {
  public void my_method() {
     ........
  }
};

May be used as method parameter.

Можно создать только изнутри того где он, если private. Если public - то извне имея экземпляр ecnlosing класса.

• encapsulation, name hiding
• при создании получает ссылку на класс в котором он и имеет доступ ко всему в нем.

OuterClass.this - ссылка на enclosing class внутри Inner

Cоздать public Inner Class:

dn.new Inner(); //dn - экземпляр enclosing class

в нестатических методах вызывается OuterClass.InnerClass enclosing class [ɪnˈkləʊz] - в котором он

An enum is a kind of class and an annotation is a kind of interface. Every array also belongs to a class that is reflected as a Class object that is shared by all arrays with the same element type and number of dimensions. The primitive Java types (boolean, byte, char, short, int, long, float, and double), and the keyword void are also represented as Class objects.

@Id Идентификатор для Entity хотябы один какой нибудь должент быть

@GeneratedValue only integer types (short, int, long) will be portably supported. Hibernate will generate the value when the save/persist occurs. Для portability prefer using the SEQUENCE generator over IDENTITY.

есть ещё JPA javax.persistence.SequenceGenerator

Универсальное решение:

       @Id
	@GenericGenerator(name = "XyzIdGenerator",
	        strategy = "myrest.IdGenerator")
	@GeneratedValue(generator = "XyzIdGenerator")
	private int id;


import java.io.Serializable;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.hibernate.HibernateException;
import org.hibernate.engine.spi.SharedSessionContractImplementor;
import org.hibernate.id.IdentifierGenerator;

import myrest.entity.Job;
import myrest.entity.Project;

public class IdGenerator implements IdentifierGenerator {


@Override
public Serializable generate(SharedSessionContractImplementor session, Object object) throws HibernateException {

    Connection connection = session.connection();
    try {
    	PreparedStatement ps;
    	if(object instanceof Project) {
    		ps = connection
                    .prepareStatement("SELECT MAX(id) as vlaue from public.project");
    	}else if(object instanceof Job) {
    		ps = connection
                    .prepareStatement("SELECT MAX(id) as vlaue from public.job");
    	}else
    		return null;
        ResultSet rs = ps.executeQuery();
        if (rs.next()) {
            int id = rs.getInt("vlaue") + 1;
            //String code = prefix + new Integer(id).toString();
            System.out.println("Generated Stock Code: " + id);
            return id;
        }

    } catch (SQLException e) {
        e.printStackTrace();
    }
    return null;
}

}

Maven org.hibernate - groupId

• hibernate-core
• hibernate-entitymanager (3.3.2.GA)
• hibernate-validator (4.1.0.Final)
• hibernate-annotations (3.3.0.GA)

• Configuration Object(database connection, Class Mapping Setup) ->
• SessionFactory Object - thread safe, per database ->
• Session Object - not usually thread safe - designed to be instantiated each time an interaction is needed with the database - Persistent objects are saved and retrieved through this. which should be thought of as a corollary to a "unit of work".
• Transaction Object - optional object - underlying transaction manager and transaction (from JDBC or JTA)
• Query Object - use SQL or Hibernate Query Language (HQL) string = used to bind query parameters, limit the number of results returned by the query, and finally to execute the query.
• Criteria Object - criteria queries ???????

dom4j

XML parsing

Xalan

XSLT Processor

Xerces

The Xerces Java Parser

cglib

changes to Java classes at runtime

log4j

.

Commons

Logging, Email etc.

SLF4J

Logging Facade for Java

• if we need to modify the design of our database after having developed a few pages or our

application

• loading and storing objects in a relational database:

  Granularity

  [ˌɡrænjʊˈlærɪtɪ]

  Inheritance

  nothing similar

  Identity

  RDBMS - key, java - (a==b) and object equality (a.equals(b)).

  Associations

  java - object references, RDBMS - foreign keys

  Navigation

  access diff

HQL (Hibernate Query Language) is the object-oriented version of SQL . It generates database independent queries

Disabling contextual LOB creation as createClob() method threw error : java.lang.reflect.InvocationTargetException

<property name="hibernate.temp.use_jdbc_metadata_defaults">false</property>

• https://github.com/hibernate/hibernate-demos/blob/master/hibernate-orm/core/Basic/src/main/java/org/hibernate/brmeyer/demo/entity/Project.java

JPA specification defines a different bootstrap process that uses its own configuration file named persistence.xml entitymanager/src/test/resources/META-INF/persistence.xml

the persistence provider (Hibernate in this case)

persistence.xml files should provide a unique name for each "persistence unit". Applications use this name to reference the configuration when obtaining an javax.persistence.EntityManagerFactory reference.

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
             version="2.0">

    <persistence-unit name="org.hibernate.tutorial.jpa">
        <description>
            Persistence unit for the JPA tutorial of the Hibernate Getting Started Guide
        </description>

        <class>org.hibernate.tutorial.em.Event</class>

        <properties>
            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:db1;DB_CLOSE_DELAY=-1;MVCC=TRUE" />
            <property name="javax.persistence.jdbc.user" value="sa" />
            <property name="javax.persistence.jdbc.password" value="" />

            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.hbm2ddl.auto" value="create" />
        </properties>

    </persistence-unit>

</persistence>

import java.util.Date;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public class EntityManagerIllustrationTest extends TestCase {
        private EntityManagerFactory entityManagerFactory;

        @Override
        protected void setUp() throws Exception {
                // like discussed with regards to SessionFactory, an EntityManagerFactory is set up once for an application
                //              IMPORTANT: notice how the name here matches the name we gave the persistence-unit in persistence.xml!
                entityManagerFactory = Persistence.createEntityManagerFactory( "org.hibernate.tutorial.jpa" );
        }

        @Override
        protected void tearDown() throws Exception {
                entityManagerFactory.close();
        }

        public void testBasicUsage() {
                // create a couple of events...
                EntityManager entityManager = entityManagerFactory.createEntityManager();
                entityManager.getTransaction().begin();
                entityManager.persist( new Event( "Our very first event!", new Date() ) );
                entityManager.persist( new Event( "A follow up event", new Date() ) );
                entityManager.getTransaction().commit();
                entityManager.close();

                // now lets pull events from the database and list them
                entityManager = entityManagerFactory.createEntityManager();
                entityManager.getTransaction().begin();
        List<Event> result = entityManager.createQuery( "from Event", Event.class ).getResultList();
                for ( Event event : result ) {
                        System.out.println( "Event (" + event.getDate() + ") : " + event.getTitle() );
                }
        entityManager.getTransaction().commit();
        entityManager.close();
        }
}

java.util.Date, should map to a SQL DATE, TIME, or TIMESTAMP datatype

@Temporal(TemporalType.TIMESTAMP)
@Column(name = "EVENT_DATE")
public Date getDate() {
    return date;
}

LocalDate in Java 8

• https://www.thoughts-on-java.org/map-date-time-api-jpa-2-2/
• https://download.oracle.com/otndocs/jcp/jdbc-4_2-mrel2-eval-spec/index.html

Hibernate Query Language (HQL) and Java Persistence Query Language (JPQL) - object focused query languages.

• JPQL subset of HQL

• non-type-safe, type-safe approach - use Criteria

   //insert
   Session session = sessionFactory.openSession();
   session.beginTransaction();
   session.save( new Event( "Our very first event!", new Date() ) );
   session.save( new Event( "A follow up event", new Date() ) );
   session.getTransaction().commit();
   session.close();
  
  
   //get
   session = sessionFactory.openSession();
   session.beginTransaction();
   List result = session.createQuery( "from Event" ).list(); //HQL Event - mapped class!
   for ( Event event : (List<Event>) result ) {
       System.out.println( "Event (" + event.getDate() + ") : " + event.getTitle() );
   }
   session.getTransaction().commit();
   session.close();
  

Parameters

:timestamp" ).setParameter( "timestamp", timestamp, TemporalType.DATE );
"where p.name like ?1" ).setParameter( 1, "J%" );

херня этот JPQL

• Cannot create TypedQuery for query with more than one return using requested result type [myrest.Model.Project]
• org.hibernate.exception.SQLGrammarException: could not extract ResultSet

Each database vendor uses a subset and superset of ANSI SQL defined syntax. Determine the proper Dialect to use by asking some questions of the JDBC Connection during bootstrap.

org.hibernate.dialect.Dialect

hibernate.dialect - may be set manually

• 7.11 http://docs.jboss.org/hibernate/orm/5.3/userguide/html_single/Hibernate_User_Guide.html
• https://docs.jboss.org/hibernate/orm/5.3/javadocs/org/hibernate/dialect/package-summary.html

org.hibernate.dialect.:

• Caché
• CUBRID
• DB2
• Derby
• Firebird
• Frontbase
• H2
• SAP HANA database
• HyperSQL
• Informix
• Ingres
• Interbase
• JDataStore
• McKoi
• Mimer
• MySQL
• MariaDB
• Oracle
• Pointbaes
• PostgreSQL
• Progress
• SAPDB/MAXDB
• SQLServer
• Sybase
• Teradata
• TimesTen

@ManyToOne

class Phone {
        private int id;

        @ManyToOne
        @JoinColumn(name = "person_id",
                        foreignKey = @ForeignKey(name = "PERSON_ID_FK")
        )
        private Person person;

ALTER TABLE Phone
ADD CONSTRAINT PERSON_ID_FK
FOREIGN KEY (person_id) REFERENCES Person

@OneToMany

@OneToMany(mappedBy = "project", fetch = FetchType.LAZY) //project
	private List<Job> job = new ArrayList<>();

project - field in Job class. which has @ManyToOne - bidirectional mapping

• SessionFactory - should be only one. thread-safe.
• Seassin - single-threaded, short-lived object
• Transaction - single-threaded, to demarcate individual physical transaction boundaries

• https://stackoverflow.com/questions/3820897/jpa-entity-without-id
• https://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#No_Primary_Key

Solutions:

1. composite, multi-column primary key.
2. Id at any unique field.
3. create id field in class with @Id @GeneratedValue(strategy=GenerationType.NATIVE) ????
4. this code

Criteria c = session.createCriteria(Product.class, "product");
c.createAlias("product.categories", "category");
c.add(Restrictions.eq("category.id", 3));

where Table (product_category) with foreigh keys p_id, c_id

session.createQuery("from project"); Immutable collections cannot be modified

@Column(name = "id_state", insertable = false, updatable = false)

relation "hibernate_sequence" does not exist In Postgres or Oracle, they use sequence tables. Since you didn't specify a sequence table name, it will look for a sequence table named hibernate_sequence

(should be mapped with insert="false" update="false") - repeated column:

@Column(name = "id_state", insertable = false, updatable = false)

5.10. Working with detached data

• Объекты нужно аттачить к "persistence context".
• Есть несколько способов, но ошибку "reassociated object has dirty collection reference (or an array)" не обойти

https://infotechgems.blogspot.com/2011/11/java-collections-performance-time.html

• Sequence(tuple) : linked list, Stack(LIFO), Queue(FIFO)
• Dynamic arrays - imp. ArrayList
• Associative array (or map) (implementation hashtable)
• sorted table - Red-black tree(SortedSet, SortedMap).
• Trees

in java:

Resizable array

Object[]

(no term)

Hash table + Linked list

(no term)

Bit Vector (EnumSet)

(no term)

Priority Heap

(no term)

Skip List

Red-black tree (set/map) - kind of Self-balancing binary search tree, fast lookup

• Сбалансированность достигается за счёт - красности или черности узла.
• Двои́чное де́рево - у каждого узла не более двух потомков

Hash table алгоритм разрешения коллизий Метод цепочек (Separate chaining). Each bucket has list.

• Constructor:

  initial capacity

  number of buckets [ˈbʌkɪt](хэши). default(16), удваивается.

  load factor

  measure of how full the hash table is allowed to get before its capacity is automatically increased .default(.75). > - less memory, slow, < - more memory, faster.

fixed size, multidimentional.

int[] anArray = new int[10]; //declaration and memory allocation
System.arraycopy(copyFrom, 2, copyTo, 0, 7); //copy

java.util.Arrays - copying, sorting and searching, comparing, filtering

Interfaces

in OOP generally form a hierarchy. to be manupulated independently of the details.

Implementations

.

Algorithms

searching, sorting on objects that implement interfaces.(polymorphic)

• Collection: size(), isEmpty(), contains(Object), iterator(), add().
• Set:
• List: Positional(access. search), ListIterator(hasPrevious(), previous(), set(),add())
• Queue: offer() - without exception, poll() - get head, element() - get but does not remove, peek() - get not remove without exception.
• Deque: Insert, Remove, Retrive. removeFirstOccurence()
• Map: basic (put, get, remove, containsKey, containsValue), bulk (putAll, clear), views( keySet, entrySet, values)
• SortedSet: range-view, first, last, get comparator.

1. for-each

for (Object o : collection)
    System.out.println(o);

1. Iterator<E> Collection.iterator() [ˈɪtəˌreɪt]

public interface Iterator<E> {
    boolean hasNext(); //условие для продолжения
    E next();  //get
    void remove(); //only safe way to modify a collection during iteration
}
    for (Iterator<?> it = c.iterator(); it.hasNext(); )
        if (!cond(it.next()))
            it.remove();


 while (iter.hasNext()) {
        ? ii = i.next()
        if (ii = 2)
            i.remove()
    }

У Linked list есть descendingIterator(). В обратном порядке.x

1. Aggreage Operations (SE 8)

  myShapesCollection.parallelStream() //or just .stream()
  .forEach(e -> System.out.println(e.getName()));

  String joined = elements.stream()
  .map(Object::toString)
  .collect(Collectors.joining(", "));

Map Keys:

for (Iterator<Type> it = m.keySet().iterator(); it.hasNext(); )
   if (it.next().isBogus())
       it.remove();

Key-value:

for (Map.Entry<KeyType, ValType> e : m.entrySet())
   System.out.println(e.getKey() + ": " + e.getValue());

1.5

• java.util.Arrays.sort(Primitives[]) - tuned quicksort n*log(n) - faster
• java.util.Arrays.sort(Object[]) - modified mergesort n*log(n)

stable: equal elements will not be reordered as a result of the sort

1.7

• java.util.Arrays.sort(Primitives[]) - Dual-Pivot Quicksort O(n log(n))

java.util.Arrays.sort(Object[]) - stable, adaptive, iterative mergesort n lg(n) (десятичный логарифм) Dual-Pivot Quicksort

• Arrays.binarySearch поиск элемента, List должен быть заранее отсортирован. O(log n)
• Collections.sort(List<T> list) - n2 log(n) for linked list

Quicksort - 1) взять элемент 2) все меньше его - до, больше - после, 3) повторить Merge sort - 1) сортировка пары 2) новая часть пары - из 2 предыдущих 3) повторить

Comparable interface - natural ordering. mutually comparable - взаимно сравнимы e1.compareTo(e2)

It is strongly recommended (though not required) that natural orderings be consistent with equals. Elements of set or map must be immutable:

• equal() = true когда copareTo = 0.
• hashCode() - Equal objects must have equal hash codes.

Collections.sort(list, comparator)

static final Comparator<Employee> SENIORITY_ORDER =
                                        new Comparator<Employee>() {
            public int compare(Employee e1, Employee e2) {
                return e2.hireDate().compareTo(e1.hireDate());
            }
    };
Collections.sort(e, SENIORITY_ORDER);

int binarySearch(List<? extends Comparable<? super T>> list, T key)

List must be sorted into ascending order according to the natural ordering of its elements Разделяя на две части - самый быстрый способ.

if not RandomAccess interface. O(n) link traversals and O(log n) element comparisons.

good for ArrayList, AttributeList, CopyOnWriteArrayList, RoleList, RoleUnresolvedList, Stack, Vector

conversion constructor

all general-purpose collection implementations have a constructor that takes a Collection argument.

mutation

When using the new aggregate operations and lambda expressions, you must take care to avoid mutation so as not

to introduce problems in the future, should your code be run later from a parallel stream.

Always refer to implementation by generic interface.

Set - prohibition is that it is not permissible for a set to contain itself as an element.

Remove duplicates:

Collection<Type> noDups = new HashSet<Type>(c);

Preserves the order of the original collection while removing duplicate elements:

Collection<Type> noDups = new LinkedHashSet<Type>(c);

Переопределил equals() должен переопределить и hashcode()

1 byte в LinkedList. Node : 3 ссылки- следующий, предыдущий и на объект. 32bits(4 byte)*3=12 + Сам объект Node - 8 байт. = 20. Размер каждого объекта в Java кратен 8. = 24. + Упакованный байт = 8 байт = около 32байт.

1 byte в ArrayList = 1байт

Rule: you should be thinking about the interfaces, not the implementations.

Primitives? Fixed size? - Arrays. Not Primitives? Convenience Implementations Rarely modified but frequently iterated. CopyOnWriteArraySet or list - totally unmodifiable.

each key to multiple values

Map<String, List<String>> m = new HashMap<String, List<String>>();
m.put(alpha, l=new ArrayList<String>()); //List<String> l;

intefcace Map.Entry<K,V> implementations:

• AbstractMap.SimpleEntry
• AbstractMap.SimpleImmutableEntry

множество элементов, одновременно не принадлежащих обоим исходным коллекциям

c = ArrayList-A.retainAll(B) // пересечение A и B
a.addAll(b) //объединяем
a.removeAll(c).

2003 as a response to the complexity of the early J2EE. It integrates with carefully selected individual specifications from the EE umbrella.

Spring family of projects - Pivotal Software.

Spring projects have been built on top of the Spring Framework

Spring Framework - app. framework and inversion of control container.

As addition or replacement to Enterprise JavaBeans (EJB) model.

Независимость классов друг от друга нужна для: to reuse to test

Early app server. Today, with the help of Spring Boot, applications are created in a devops- and cloud-friendly way.

The ApplicationContext container includes all functionality

org.springframework.context.ApplicationContext interface

managed objects or beans or Spring Beans - описываются XML или анотацией или in-code - bean definition - metadata. из POJO. Object managed by the Spring IoC container.

Bean создается:

dependency lookup

вызывающий спрашивает контейнер дать bean по имени ил типу (Locator pattern).

dependency injection

контейнер передает объекты по имени другим объектам через конструктор, свойство или Factory method

org.springframework.beans org.springframework.context

org.springframework.beans.factory. BeanFactory interface - configuration framework and basic functionality

org.springframework.context. ApplicationContext interface and WebApplicationContext - adds more enterprise-specific functionality.

• instantiating, configuring, and assembling beans.

Spring Boot, Spring Security, Spring Data, Spring Cloud, Spring Batch.

Spring Core Container

BeanFactory and ApplicationContext

(no term)

Aspect-oriented programming :

Authentication and authorization

via Spring Security sub-project

Convention over configuration

offered in the Spring Roo module

Data access

using JDBC and ORM tools and NoSQL databases

Inversion of control container

– What is the benefit of centralized lifecycle management to reuse to test – Programming to interfaces – Leveraging the power of proxies – Understanding the template pattern

• Central Maven Repository (effective pom) - http://search.maven.org/
• Java.Net Maven repositories - http://maven.java.net/

Направленный ациклический граф или направленный лес

орграф, в котором отсутствуют направленные циклы, но могут быть «параллельные» пути, выходящие из одного узла и разными путями приходящие в конечный узел.

Следит за изменениями файлов

Software test - piece of software thich executes another piece of software state testuing - result. behavior - expected sequence of events. 1) Unit testing without dependencies (in isolation)

unit - class or method

test doubles - replacements for real dependencies:

dummy object

passed around but never used

Fake

objects have working implementations, but are usually simplified

stub

class !partial implementation for an interface or class with the purpose of using an instance of this stub class during testing. Also used for recording calls.

mock

object! dummy implementation for an interface or a class in which you define the output of certain method calls. May record the interaction with the system. Mock is an English word which means to mimic or to imitate.

TDD Test-Driven Development - test before code

2) Integration tests component or the integration between a set of components. test of dependencies. 3) Performace tests are used to benchmark [ˈbɛntʃˌmɑːk] software components repeatedly. benchmark - тест производительности, система тестирования производительности.

Maven Surefire Plugin scan

• \**/Test*.java
• **/*Test.java
• **/*Tests.java
• **/*TestCase.java

for JUNIT 4.12

• use should in test - public void ordersShouldBeCreated (){

package job1;

import static org.junit.Assert.assertEquals;
import java.util.List;
import org.junit.Test;

public class TestMain {

        @Test
        public void RangeToList4Test(){
                List<String> IPs = Main.getListFromRange("192.168.0.1", "192.168.0.3");
                assertEquals(IPs.size(), 3);
                assertEquals(IPs.contains("192.168.0.1"), true);
                assertEquals(IPs.contains("192.168.0.2"), true);
                assertEquals(IPs.contains("192.168.0.3"), true);
        }

        @Test
        public void RangeToList3Test(){
                List<String> IPs = Main.getListFromRange("192.168.0.1", "192.168.1.3");
                assertEquals(IPs.size(), 258);
                assertEquals(IPs.contains("192.168.0.255"), true);
                assertEquals(IPs.contains("192.168.0.2"), true);
                assertEquals(IPs.contains("192.168.1.2"), true);
                assertEquals(IPs.contains("192.168.1.3"), true);
        }

}

• fail([message])
• assertTrue([message,] boolean condition)
• assertFalse([message,] boolean condition)
• Checks that the boolean condition is false.
• assertEquals([message,] expected, actual)
• assertEquals([message,] expected, actual, tolerance) //for float - The tolerance is the number of decimals which must be the sam
• assertNull([message,] object)
• assertNotNull([message,] object)
• assertSame([message,] expected, actual) //Checks that both variables refer to the same object.
• assertNotSame([message,] expected, actual)

Mockito is a popular mock framework

https://www.oracle.com/technetwork/java/javase/documentation/spec-136004.html

Used in

Architecture. is a POJO that is serializable, has a no-argument constructor, and allows access to properties using getter and setter methods that follow a simple naming convention.

The required conventions are as follows:

• must have a public default constructor (with no arguments).
• The class properties must be accessible using get, set, is (can be used for boolean properties instead of get), to and other methods (so-called accessor methods and mutator methods) according to a standard naming convention. This allows easy automated inspection and updating of bean state within frameworks, many of which include custom editors for various types of properties. Setters can have one or more than one argument.
• The class should be serializable.

MUST implement the Serializable interface. java.beans J2SE Reusable software component written in JAVA that can be manipulated visually in an application builder tool

public class PersonBean implements java.io.Serializable {
    private String name;
    private boolean deceased;

    // Методы геттеры (get) и сеттеры (set)
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public boolean isDeceased() {
        return deceased;
    }
    public void setDeceased(boolean deceased) {
        this.deceased = deceased;
    }

    //Переопределенные методы equals() и hashCode()
    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }

        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        PersonBean that = (PersonBean) o;

        if (deceased != that.deceased) {
            return false;
        }

        return !(name != null ? !name.equals(that.name) : that.name != null);
    }


    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + (deceased ? 1 : 0);
        return result;
    }

    //Переопределенный метод toString()
    @Override
    public String toString() {
        return "PersonBean{" +
                "name='" + name + '\'' +
                ", deceased=" + deceased +
                '}';
    }
}

• https://checkerframework.org/jsr308/specification/java-annotation-design.html
• https://docs.oracle.com/javase/tutorial/java/annotations/type_annotations.html

Before SE 8 annotations could only be applied to declarations. Now annotations can also be applied to any type use.

This includes the new operator, type casts, implements clauses and throws clauses. Type Annotations allow improved analysis of Java code and can ensure even stronger type checking.

Java 8 only provides the ability to define these types of annotations. It is then up to framework and tool developers to actually make use of it.

• https://www.oracle.com/webfolder/technetwork/tutorials/obe/java/Lambda-QuickStart/index.html

Это более компактная форма single-method class

• Optional type declaration
• Optional parenthesis around single parameter
• Optional curly braces
• Optional return keyword

@FunctionalInterface //просто показывает всем, что это для лямбд
interface MathOperation { //интерфейс который реализует наша lambda expression
      int operation(int a, int b);
}

 MathOperation multiplication = (int a, int b) -> { return a * b; };
 MathOperation multiplication = a -> a++; //MathOperation - *target type*

the Java compiler uses the target type of the context or situation in which the lambda expression was found.

java.util.function Предопределенные функциональные интерфейсы:

• Predicate<T> - one argument, return boolean.
• Consumer<T> - one argument, no return.
• Supplier<T> - no argument, return result.
• Function<T,R> - one argument, return result.
• UnaryOperator<T> extends Function<T,T> - one argument, return same type return
• BiConsumer<T,U> - no return.
• BiFunction<T,U,R> - two arguments, return result.
• BinaryOperator<T> extends BiFunction<T,T,T> - two operands of the same type, return same type

Lambda vs Closure Closure It makes it possible for a function to have "private" variables. Lambda is not indendet for that.

• Static methods
• Instance methods
• Constructors using new operator (TreeSet::new)

added for backward compatibility so that old interfaces can be used to leverage the lambda expression capability

public interface vehicle { default void print() { System.out.println("I am a vehicle!"); } }

Collection interface: Stream<E> stream() and Stream<E> parallelStream(), for obtaining sequential or parallel streams from the underlying collection. Aggregate operations - over collections.

Collection.sort( comparing(Apple::getWeight));

http://www.defmacro.org/2006/06/19/fp.html https://dzone.com/articles/functional-programming-patterns-with-java-8

@see #field @see #Constructor(Type, Type…) @see #Constructor(Type id, Type id…) @see #method(Type, Type,…) @see #method(Type id, Type, id…) @see Class @see Class#field @see Class#Constructor(Type, Type…) @see Class#Constructor(Type id, Type id) @see Class#method(Type, Type,…) @see Class#method(Type id, Type id,…) @see package.Class @see package.Class#field @see package.Class#Constructor(Type, Type…) @see package.Class#Constructor(Type id, Type id) @see package.Class#method(Type, Type,…) @see package.Class#method(Type id, Type, id) @see package

Equivalent to <code>{@literal}</code>.

should be listed alphabetically by the exception names.

tags should be listed in chronological order, with the creator of the class listed at the top.

• HTML 3.2 https://www.w3.org/TR/2018/SPSD-html32-20180315/
• HTML latest spec https://www.w3.org/TR/html/

HTML Hypertext Markup Language (HTML) [ˈhaɪpə,tɛkst] [mɑrkʌp] [ˈlæŋɡwɪdʒ]

Hypertext is text displayed on a computer display or other electronic devices with references (hyperlinks) to other text

• parent - <div><span></span></div> - div - parent for span

how to access Web service - machine to machine in WWW - information space where документы и ресурсы идентифицируются по Uniform Resource Locators (URLs) взаимосвязыаны в hyperlinks - тест с ссылкамиx

JAX-RS: Java API for RESTful Web Services (JAX-RS) - Java API spec

javax.ws.rs

Implemented:

• in Java EE to Java EE container
• jersey.github.io - Oracle, embadded server

• https://developer.github.com/v4/
• https://graphql.org/
• The spec determines the validity of the schema on the API server. The schema determines the validity of client calls.
• The schema defines an API's type system and all object relationships.
• A client can query the schema for details about the schema.
• The shape of a GraphQL call mirrors the shape of the JSON data it returns. Nested fields let you query for and receive only the data you specify in a single round trip.
• GraphQL is not a storage model or a database query language. The graph refers to graph structures defined in the schema, where nodes define objects and edges define relationships between objects. The API traverses and returns application data based on the schema definitions, independent of how the data is stored.
• GraphQL lets you replace multiple REST requests with a single call to fetch the data you specify.
• you may need to rely on both the docs and the schema validation to successfully call the GraphQL API.

solving two problems:

• scalability - responses were filled with hints in the JSON responses to help people continue to navigate through the API. required two or three separate calls to assemble a complete view of a resource.
• We wanted to generate documentation from our code. type-safety for user-supplied parameters

data serialization format

Object - an unordered collection

JavaScript Object Notation language-independent data format. { "name" : " aa" }

Number

a signed decimal number that may contain a fractional part and may use exponential E notation

String

a sequence of zero or more Unicode characters. ""

Boolean

either of the values true or false

Array

an ordered list of zero or more values "ar" : [\n],

Object

like array but associative arrays. Recomendated: all key unique. {

null

An empty value, using the word null. Ex. "spouse": null

Недостатки: нельзя бинарные объекты

superset of JSON

unordered Objects

if order required sequence must be used - []

Uniform Resource Locator (URL) is a specific type of Uniform Resource Identifier (URI) URL - web adress, used in browsers.

Разница:

• URI - может быть URL, а может быть короче

• URL - это всегда URI = scheme:[//authority]path[?query][#fragment] - как минимум http://path

  Абсолютные URI mailto:John.Doe@example.com data:text/plain;charset=iso-8859-7,%be%be%be Относительные URI relative/URI/with/absolute/path/to/resource.txt //example.org/scheme-relative/URI/with/absolute/path/to/resource.txt ..../../resource.txt /resource.txt#frag01 #frag01

Extensible Markup Language (XML) [ɪkˈstɛnsəbəl] is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable.

Cascading Style Sheets (CSS)(.css) - separation of presentation and content, such as layout, colors, and fonts. Cascading comes from the specified priority scheme to determine which style rule applies if more than one rule matches a particular element.

• more flexibility
• control in the specification of presentation characteristics
• style reusing
• different rendering methods, such as on-screen, in print, by voice, mobile device
• Classes and IDs are case-sensitive - start a-Z, can include 0-9,-,_

h1 {color: red; text-align: center;} - one rule.

Consist of rule-sets:

selectors

which part of the markup a style applies to

declaration block

list of declarations in braces - property:value.

Pseudo-classes

- h1:hover {}

Not recomended:

• Inline Styles <h1 style="color:red; font-size:30px;">

Всегда в Head:

<head> <link href="path/to/file.css" rel="stylesheet" type="text/css"> </head>

• from scratch
• WordPress, Drupal, Bitrix, Tumblr or Joomla - theme, design, and templates -“content management systems” CMS

• Bootstrap provides basic style definitions for all HTML elements
• end result is a uniform appearance for prose, tables and form elements across web browsers
• CSS classes in Bootstrap: light- and dark-colored tables, page headings, more prominent pull quotes, and text with a highlight.
• JavaScript components in the form of jQuery plugins - dialog boxs, tooltips, and carousels
• Bootstrap component consists of an HTML structure, CSS declarations, and in some cases accompanying JavaScript code.
• auto-complete function for input fields
• layout components. basic layout component - Container - other elements in it.
• fixed-width and fluid-width container
• after container is placed - layout components implement a CSS grid layout
• A precompiled version of Bootstrap - one CSS file and three JavaScript files
• bootstrap.min. как и компилированные «облегченные» файлы

null is a keyword in Java. только строчными! null - default value for any reference type null - special type without name

can be used with = and !

java.lang.NullPointerException

An instance of Enum in Java is created when any Enum constants are first called or referenced in code.

public class Main {
        public enum C {
                PENNY(1,2), NICKLE(2,3), DIME(3,5), QUARTER(4,0);
                int i;
                   private C(int i, int g) { //must be private
                           this.i=i;
            System.out.println("wtf");
            };

                   public void a() {
                           System.out.println(this.name() + this.i);
                   }
                };
        public static void main(String[] args) {
                C a = C.NICKLE;
                a.a();
        }
}

out: wtf wtf wtf wtf NICKLE2

By default, assertions are disabled at runtime. Used in developing stage to confirms your assumptions about the behavior of your program

assert Expression1 ;

if it is false throws an AssertionError with no detail message.

assert Expression1 : exp2 ;

exp2 - String mesage, or object for AssertionError constructor, cannot be method call that return void

To enable assertions at various granularities, use the -enableassertions, or -ea, switch.

java -ea package/ MainClass

Examples:

assert Thread.holdsLock(this); // in private method called by synchonized public one

• varible not modify
• method not override
• class not extend
• inner anonymouse class may access only final varibles
• constructor cannot be final

• abstract class
• abstract - метод должен быть марекрован если у него нет реализации в Abstract Class.

[ˈkəʊlən]

1. Jump-out label

label: for {
    break label;
}
Lbl1: {
    if(x == 0) break Lbl1;
}
Lbl2:{
    if(x > 0) break Lbl1;
}

1. Ternary condition

= true ? 1 : 0 ;

1. for-each

for (String s: ss) { print(s);}

1. Asserion

// throws an AssertionError with the message if the condition evaluates to false
assert a >= 0: "factorial may not be less than 0";

1. Case in switch statement

switch (type) {
    case WHITESPACE:
    case RETURN:
        break;
    case NUMBER:
        print("got number: " + value);
        break;
    default:
        print("syntax error");
}

1. Method references

Person::compareByAge //Person - class, compareByAge - static method

Java 8 используется для упрощения lambda выраженийx

List<String> strings = Arrays.asList("one","two");
strings.forEach(System.out::println);

Function<Computer, Integer> getAge = Computer::getAge; //Computer - return
Integer computerAge = getAge.apply(c1); //call

Consumer<String> c = System.out::println;

Evolution of "comparator" :

Comparator c = (Computer c1, Computer c2) -> c1.getAge().compareTo(c2.getAge());
Comparator c = (c1, c2) -> c1.getAge().compareTo(c2.getAge());
Comparator c = Comparator.comparing(Computer::getAge);

Constructor reference :

Supplier aa = Calibreble::new; //java.util.function.Supplier - no arguments
Function<Integer, Calibreble> aa = Calibreble::new; // - argument int.
BiFunction<Integer, Integer, Calibreble> //two arguments

single, uppercase letters

• E - Element (used extensively by the Java Collections Framework)
• K - Key
• N - Number
• T - Type
• V - Value
• S,U,V etc. - 2nd, 3rd, 4th types

threads mostly time slicing - разделение CPU между процессами concurrently of if multiple [ˈmʌltɪp] processors are available, actuallly - simultaneously [ ˌsaɪməltəˈniːɪtɪ] begin to interfere [ˌɪntəˈfɪə] with each other

process [ˈprəʊsɛs] has its own memory space. between processes(and on dif systems) - Inter Process Communication (IPC) resources, such as pipes and socket java.lang.ProcessBuilder

threads [θrɛd] threads share the process's resource - memory and open files

Class java.lang.Thread implements Runnable

• has a priority. Initially priority of the creating thread.
• daemon or not. same
• has name(default - generated)
• holds lock on the specific object ???

At start single non-daemon thread usually. Until:

• exit() of Runnable and the security manager has permitted the exit (System.
• all not daemon threads by returning or by throwing an exception.

To create:

1. extend Thread

new Class().start()

1. implement Runnable

new Thread(new Class()).start()

1. anonymous Runnable

new Thread(new Runnable() {
           public void run() { alphonse.bow(gaston); }
     }).start();

Thread.sleep(4000); //4 sec,(static) put current executing thread to sleep.

InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

Thread.isAlive() - been started and not yet died

Thread.currentThread() - (static) ref to executing object

Enum Thread.State:

• NEW not alive, never started
• RUNNABLE started, not running, alive
• BLOCKED monitor lock
• WAITING(wait, join,LockSupport.park), TIMED_WAITING, TERMINATED.

Daemon Thread.setDaemon() и isDaemon()

ThreadGroup class Группа указывается при создании потока. Методы activeCount() и enumerate() возвращают количество и полный список, соответственно, всех потоков в группе.

Каждый объект в Java имеет не только блокировку для synchronized блоков и методов, но и так называемый wait-set.

MUST be in synchronized блоках на этом объекте или в synchronized методах внутри этого объекта.

It is recommended that applications not use wait, notify, or notifyAll on Thread instances.

wait

wait for notify() or notifyAll(). На любом объекте, и поток попадает в его wait-set.

notify

useful only in massively parallel applications — that is, programs with a large number of threads, all doing similar chores.

notifyAll

flag = true;
notifyAll(); //for guarded blocks

[ˌɪntəˈrʌpt] - indication to a thread that it should change something. Thread.interrupt()

Thread.interrupted(),isInterrupted() - check status

1. Thread.checkAccess() executed.
2. If Wait, Join, Sleep - interrupt status cleared, InterruptedException. If blocked in a Selector - interrupt status will be set. return immediately from the selection operation
3. else interrupt status will be set. Interrupting a thread that is not alive need not have any effect.

wait for the completion of thread.

t.join(); t.join(4000); //wait forever or loop for this.isAlive

Errors:

thread interference

[ˌɪntəˈfɪərəns] записывают и читают одно и то же

memory consistency errors

[kənˈsɪstənsɪ] [ˈerər] inconsistent views of what should be the same data

deadlock

block, waiting for each other.

Starvation

e.g. huge synchronized method block object for long time.

Livelock

e.g. people talk to each other as a response, too busy responding to each other to resume work.

happens-before relationship - guarantee that memory writes by one specific statement are visible to another specific statement

1. synchronized methods - synchronized

not possible for two invocations to interleave [ˌɪntəˈliːv]

• constructors cannot be synchronized
• lock at method's object that provides the intrinsic lock
• thread can acquire a lock that it already owns - reentrant synchronization - prevent selfblock
• two synchronized methods in one object may couse deadlock if call synchonized method of another object from synchonized method
• synchronized statements
• reduce synchonized methods amount and deadlocks
• fine-grained synchronization

synchronized(this) {
   }

intrinsic lock or monitor lock - internal entity for synchronization in every object 1) exclusive access 2) happens-before relationship

When a thread releases an intrinsic lock, a happens-before relationship is established between that action and any subsequent acquisition of the same lock.

Rule : Maximum reliance on immutable objects is widely accepted as a sound strategy for creating simple, reliable code.

working loop is wasteful while(!joy) {} we need wait

public volatile boolanen joy;

synchronized(lock) {
    // This guard only loops once for each special event, which may not
    // be the event we're waiting for.
    while(!joy) {
        try {
            lock.wait(); //thanks to synchronized - *wait* uses intrinsic lock = this
        } catch (InterruptedException e) {}
    }
    System.out.println("Joy and efficiency have been achieved!");
}

• Always invoke wait inside a loop that tests for the condition being waited for.
• joy readed and writed by separate threads that is why intrinsic lock or synchronization required

java.util.concurrent

http://www.oracle.com/technetwork/articles/javase/index-140767.html

Interfaces:

• BlockingQueue
• ConcurrentMap
• approximate matches feature

Default:

• all not daemon threads by returning or by throwing an exception.
• exit() of Runnable and the security manager has permitted the exit (System.exit())

Modifies some variable to indicate that the target thread should stop running. The target thread should check this variable regularly, and return from its run. https://docs.oracle.com/javase/7/docs/technotes/guides/concurrency/threadPrimitiveDeprecation.html

private volatile Thread blinker;

    public void stop() {
        blinker = null;
    }

    public void run() {
        Thread thisThread = Thread.currentThread();
        while (blinker == thisThread) {
            try {
                Thread.sleep(interval);
            } catch (InterruptedException e){
            }
            repaint();
        }
    }

если private читается только внутки synchronized по объекту, то volatile не нужно

/for remove, get, compareTo

@Override
        public boolean equals(Object o) {
                if (!(o instanceof Contact))
                        return false;
                Contact n = (Contact) o;
                return (n.id == this.id);
        }

    public int hashCode() {
        return 31*firstName.hashCode() + lastName.hashCode();
    }
//for sort only
public int compareTo(Name n) {
        int lastCmp = lastName.compareTo(n.lastName);
        return (lastCmp != 0 ? lastCmp : firstName.compareTo(n.firstName));
    }

Private constructor to restrict instantiation of the class from other classes.

used for

• logging
• drivers objects
• caching
• thread pool.
• Abstract Factory, Builder, Prototype, Facade etc.

public enum EnumSingleton { //does not allow lazy initialization. serializable
    INSTANCE;
    int field; //not serialized http://docs.oracle.com/javase/6/docs/platform/serialization/spec/serial-arch.html#6469
}

private volatile ThreadSafeSingleton instance; //!volatile Java 1.5 (not cached)
public static ThreadSafeSingleton getInstanceUsingDoubleLocking(){
    ThreadSafeSingleton localRef = instance; // не знаю зачем это. это вопрос
    if(localRef == null){ // синхронизация нужна только для первых потоков
        synchronized (ThreadSafeSingleton.class) { //double checked locking principle. (this)-if not singleton
            localRef = instance;
            if(localRef == null){
                instance = localRef = new ThreadSafeSingleton(); //важно чтобы полностью инициализировался
            }
        }
    }
    return localRef;
}

The visitor takes the instance reference as input, and implements the goal through double dispatch.

interface CarElement {
    void accept(CarElementVisitor visitor);
}

interface CarElementVisitor {
    void visit(Body body);
    void visit(Car car);
    void visit(Engine engine);
    void visit(Wheel wheel);
}

class Car implements CarElement {
    CarElement[] elements;

    public Car() {
        this.elements = new CarElement[] {
            new Wheel("front left"), new Wheel("front right"),
            new Wheel("back left"), new Wheel("back right"),
            new Body(), new Engine()
        };
    }

    public void accept(final CarElementVisitor visitor) {
        for (CarElement elem : elements) {
            elem.accept(visitor);
        }
        visitor.visit(this);
    }
}

class Body implements CarElement {
    public void accept(final CarElementVisitor visitor) {
        visitor.visit(this);
    }
}

class Engine implements CarElement {
    public void accept(final CarElementVisitor visitor) {
        visitor.visit(this);
    }
}

class Wheel implements CarElement {

    public void accept(final CarElementVisitor visitor) {
        /*
         * accept(CarElementVisitor) in Wheel implements
         * accept(CarElementVisitor) in CarElement, so the call
         * to accept is bound at run time. This can be considered
         * the *first* dispatch.
        */
        visitor.visit(this);
    }
}

class CarElementDoVisitor implements CarElementVisitor {
    public void visit(final Body body) {
        System.out.println("Moving my body");
    }

    public void visit(final Car car) {
        System.out.println("Starting my car");
    }

    public void visit(final Wheel wheel) {
         /*each implementation of
         * CarElementVisitor implements the visit(Wheel), which is
         * another decision that is made at run time. This can be
         * considered the *second* dispatch.
         */
        System.out.println("Kicking my " + wheel.getName() + " wheel");
    }

    public void visit(final Engine engine) {
        System.out.println("Starting my engine");
    }
}

class CarElementPrintVisitor implements CarElementVisitor {
    public void visit(final Body body) {
        System.out.println("Visiting body");
    }

    public void visit(final Car car) {
        System.out.println("Visiting car");
    }

    public void visit(final Engine engine) {
        System.out.println("Visiting engine");
    }

    public void visit(final Wheel wheel) {
        System.out.println("Visiting " + wheel.getName() + " wheel");
    }
}

public class VisitorDemo {
    public static void main(final String[] args) {
        final Car car = new Car();

        car.accept(new CarElementPrintVisitor());
        car.accept(new CarElementDoVisitor());
    }
}

• https://www.oracle.com/technetwork/articles/java/json-1973242.html
• JSR 353: JavaTM API for JSON Processing https://jcp.org/en/jsr/detail?id=353
• https://habr.com/en/company/luxoft/blog/280782/
• https://ru.stackoverflow.com/questions/745094/%D0%9A%D0%B0%D0%BA-%D0%B8-%D1%87%D0%B5%D0%BC-%D0%BF%D0%B0%D1%80%D1%81%D0%B8%D1%82%D1%8C-json-%D0%BD%D0%B0-java

libs:

• json-p - JSON with padding - JSR 353 implementation org.glassfish
• json.org
• Jackson
• Google GSON
• json-lib
• javax json
• json-simple
• json-smart
• flexjson
• fastjson

• https://javaee.github.io/jsonp/
• https://search.maven.org/search?q=org.glassfish%20json

API:

• API Streaming (javax.json.stream),
• JSON API Object Model (javax.json).

<dependency>
   <groupId>org.glassfish</groupId>
   <artifactId>javax.json</artifactId>
   <version>1.0.4</version>
</dependency>

InputStream input = new FileInputStream("C:\\Users\\Chepilev_VS\\Desktop\\f\\provodki_1000.json");
//------------------- JSON API Object Model (javax.json) ------------------
        // Create JsonReader object
        JsonReader jsonReader = Json.createReader(input);


        // Get JsonObject (root object).
        JsonArray rootJSON = jsonReader.readArray(); //or readObject()

        // Close resources
        jsonReader.close();
        input.close();

        System.out.println(rootJSON.getJsonObject("address"));

 //------------------- API  Streaming ------------------

InputStream input = new FileInputStream("C:\\Users\\Chepilev_VS\\Desktop\\f\\provodki_1000.json");

        // https://javaee.github.io/javaee-spec/javadocs/javax/json/stream/JsonParser.html
        JsonParser parser = Json.createParser(input);


        // Get JsonObject (root object).
        while (parser.hasNext()) {
            JsonParser.Event event = parser.next();
            if (event == JsonParser.Event.START_OBJECT ) { //provodka
                while (parser.hasNext()) {
                    if (parser.getString().equalsIgnoreCase("naznach")) {
                        String value = parser.getString();
                    }
                }
            }
        }

        // Close resources
        parser.close();
        input.close();

Arrays.toString()

• Bash - babun
• emacs
  • emacsrun
  • M-x eval-expression RET (find-file user-init-file) RET

• main Ctrl-j psvm
• отладка Alt+F8
• find used Alt+f7
• autocompletion Ctrl+Space
• suggestions Alt+space
• вставить живой шаблон Ctrl+j
• инфа Ctrl+q or ctrl+Shift+i
• goto Ctrl+b or F4
• next occurrence F3
• rename varible shift+f6
• Настройки Сtrl+Alt+S
• Import class left Alt+Enter

• comment block Ctrl+Shift+/

Emacs mode: Ctlr+Shift+ minus undo Ctrl+Shift+z redo Ctrl+x n/p next tab

sandbox:

• tarun ideaIC-2018.2.5.tar.gz
• chown -R idea:idea idea-IC-182.4892.20/
• chmod -R o-x idea-IC-182.4892.20/

платформа расширенного клиента (RCP — от англ. rich client platform).

• Ядро платформы (загрузка Eclipse, запуск модулей);
• OSGi (стандартная среда поставки комплектов (англ. bundles));
• SWT (портируемый инструментарий виджетов); - GUI в Eclipse написан с использованием инструментария SWT
• JFace (файловые буфера, работа с текстом, текстовые редакторы);
• Рабочая среда Eclipse (панели, редакторы, проекции, мастера).

• autocmpletion Ctrl+Space
• F2 quick reference Shift+F2 documentation
• F3 goto
• Ctrl+I Ctrl+Shift+F Format
• Ctrl+/ Ctrl+Shift+/ Comment
• F12 Editor window
• Alt+Shift+J Generate element Comment

L1

help desk справочная служба. Predefined steps to resolve problem, technology does not metter. Mark as ticket or incident.

L2

require some technical knowledge. may have read access to java code

L3

They fix the code defects in the application and do small enhancements.

• Oracle Database
• MySQL
• Oracle Fusion Middleware
• Oracle Cloud
• Java language since 2010
• ERP solutions (Oracle Fusion, Oracle E-Business Suite, JD Edwards EnterpriseOne)
• Oracle Cloud

in telecommunications, stands for

operations support system

(Система эксплуатационной поддержки) computer systems used by telecommunications service providers to manage their networks

business support system

(Биллинг, CRM, ERP) a telecommunications service provider (or telco) uses to run its business operations towards customers.

OSS/J - Инициатива OSS посредством Java Её основная цель — разработка открытых стандартов на интерфейсы (API) для интеграции BSS (Систем поддержки бизнеса) и OSS (Систем эксплуатационной поддержки) (OSS/BSS) в рамках подхода NGOSS.

Удаление зависших процессов

select * from pg_stat_activity where datname = 'pmpbo-dev' AND state = 'active';
select pg_cancel_backend(<pid of the process>)

or

select pg_terminate_backend(<pid of the process>)

масштабировать свой продукт и во сколько вам это обойдётся.

• железо - С
• бизнес-логики облачных сервисов - PHP, Python
• ERP, eCommerce, CRM - 1C, SAP ABAP, MS Dynamics
• области разработки хранилищ данных - SQL, NoSQL
• фронтенд/бэкенд информационных систем - Java, JavaScript (Spring, Node.js, React, Vue и т. д.)
• SaaS - серверах/хостинге и софте. Именно они «отъедают» заметную часть бюджета, если технологии были выбраны не совсем удачно
• Mac OS - Swift

https://en.wikipedia.org/wiki/Consensus_(computer_science) A fundamental problem in distributed computing and multi-agent systems

http://www.tadviser.ru/index.php/%D0%A1%D1%82%D0%B0%D1%82%D1%8C%D1%8F:%D0%91%D0%BE%D0%BB%D1%8C%D1%88%D0%B8%D0%B5_%D0%B4%D0%B0%D0%BD%D0%BD%D1%8B%D0%B5_%28Big_Data%29

As compared to traditional technology, big data technology uses commodity hardware instead of expensive hardware.

Large and complex data sets. To extract value from data and seldom to a particular size of data set. опред размера. => Advanced data analytics methods.

• offer greater statistical power
• may lead to a higher false discovery rate
• concepts (3 Vs of big data):
  • volume[ˈvɒljuːm]
  • velocity[vɪˈlɒsɪtɪ] (noise, value) - скорость - batch, peruiduc, near Real Time, Real Time or Hot, Warm, Cold
  • variety[vəˈraɪɪtɪ] - разновидности
    • Transactions - database records
    • Files - documents, log files
    • Events - Messages, Data streams.
  • veracity [vɛˈræsɪtɪ] - достоверность

Data science:

• data mining (gather)
• from data to insight (clean)
• from insight to model (model)
• from model to value (deploy) - predicts

Architecture: require massively parallel software running on clusters or more.

• Commercial vendors historically offered parallel database management systems.
• physics experiment - high performance computing (supercomputers)
• Google - MapReduce 1. queries are split and distributed across parallel nodes and processed in parallel (the Map step). 2. results are then gathered and delivered. Adopted by an Apache project Hadoop and Spark
• MIKE2.0 methodology - pilot project for a "framework"
• multiple-layer architecture - inserts data into a parallel DBMS, which implements the use of MapReduce and Hadoop frameworks
• data lake - способ управления большими данными, когда все сбрасывается в один репозиторий файлов или blob объейктов, а потом уже анализируется.

Store

• Records - database
• documents - search?
• files - file store
• messages - Amazon SQS
• streams - Apache Kafka, Amazon shit.

Why stream storage?

• Decouple producers & consumenrs
• Persistent buffer
• Collect multiple streams
• Preserve client ordering
• Parallel consumption
• Streaming MapReduce

Delivery (deduping - data deduplication) guarantees

• at-most-once delivery - message may be lost - hight perfomance
• at-least-once delivery - may be duplicated but not lost
• exactly-once delivery - not lost and not duplicated

Отличия бизнес-аналитики от Big Data

1. формулы по результатам за период
2. данные после чистки ->
   • выдвигается гипотеза
   • строятся статистическая, визуальная и семантическая модели
   • проверяется вероятность гипотезы и выдвигается следующая

Требует от исследователя либо:

• интерпритация визуальных значений
• составление интерактивных запросов на основе знаний
• адаптивные алгоритмы машинного обучения (время жизни может быть коротким)

• appwiz.cpl - Установка удаление программ
• mstsc - RDP-client

• Фриланс - тяжело рости
• Продуктовые компании - возможность роста как повезет
• Маленький аунсорсинг - похож на фриланс, народ залипает, как повезет с професс-ю коллегами
• Большой аутсорсинг - легко менять вид деятельности, ничем не владеете, легко расти
• Enterprise( Бфнки АБВНефть Газ) - очень формальный, формальность отношений, стабильность, конференции выставки, движняк

Искать Технологии которые используют большинство аутсорсингов

Лаборатория при университете - плохо

• мобилы - плохо
• игры - плохо
• АСУТП - хорошо но тяжело найти

Заниматься тем, чем хочите

https://habr.com/en/post/308032/ защита комьютера от модификации прямого доступа незаметным образом

• apt-get install xdotool
• xdotool getmouselocation
• xdotool mousemove XXX YYY click 1

used in many Internet protocols, including TLS/SSL

A/B testing

контрольная выборка поочередно сравнивается с другими. достижения, например, наилучшей ответной реакции потребителей на маркетинговое предложение

Association rule learning

http://books.zkoss.org/zk-mvvm-book/8.0/ ViewModel is an abstraction of Model. It extracts the necessary data to be displayed on the View from one or more Model classes. Those data are exposed through getter and setter method like JavaBean's property. can not access any UI components

data binding mechanism synchronize the data automatically. This makes ViewModel and View loosely coupled.

Validation performed before saving data into ViewModel. If validation fails, the data will not be saved to ViewModel.

• @Command - event handling. onClick="@command('insert')"
• @Init - initialization method
• @NotifyChange - update field that have getter. implicit for setters.
  • @DependsOn - notify change for getters
  • dynamic - BindUtils.postNotifyChange(null, null, this, "newcontact");

ViewModel - POJO exposes its properties like JavaBean. The method's return type can be primitive type (int, boolean…), or public! JavaBean.

it will create a binder for the ViewModel and instantiate the ViewModel's class. The id is used to reference ViewModel's properties, e.g. vm.name, whilst the full-qualified class name is used to instantiate the ViewModel object itself.

<window apply="org.zkoss.bind.BindComposer"
		viewModel="@id('vm')@init('com.foo.mywebapp.MyViewModel')"

Bind value:

<intbox value="@bind(vm.index)"/>
<textbox value="@load(vm.name)"/> <!-- string -->

Propery of JavaBean (EL expression

<label value="@load(vm.address.street)"/>

List collection, field = itemList:

private int selectedIndex;
get/set selectedIndex
get List<Class> itemList

<label value="@load(vm.address.street)"/>
<listbox model="@load(vm.itemList)" selectedIndex="@bind(vm.selectedIndex)">
    <template name="model" var="item">
        <listitem label="@load(item.name)"/>
    </template>
</listbox>

ZK Bind - data binding(and events) View(ZUL) <-> ViewModel(POJO)

binding source

component's attribute

binding target

ViewModel's property or Command

in ZUL:

• @load(vm.contacts): loading data to target, id - view mode, contacts - getter
• @save(…): for saving data. - setter
• @bind getter and setter

Conditional binding @save(vm.currentBook, before='save') - save after save command.

• https://www.zkoss.org/zkdemo/input/form_sample
• spring hibernate https://emrpms.blogspot.com/2013/06/zk-mvvm-form-binding-crud-with-spring.html

https://www.zkoss.org/wiki/ZK_Getting_Started/Get_ZK_Up_and_Running_with_MVC

Eclipse: [Window] -> [Preferences] -> [Maven] –> [Archetypes], click Add Remote Catalog http://mavensync.zkoss.org/maven2/

maven: jetty:stop jetty:run. jetty:stop не нужно

http://localhost:8080/mywebapp/index.zul