JAVA overview

What is JDK? JDK is the abbreviation of Java Development Kit which contains the compiler and the interpreter needed for the developer to write the code and then compile it and finally run it.

what is the JRE? JRE is the abbreviation of Java Runtime Environment which is needed by the client to run the application

Java is based on the OOP concept, the size of the object created from the class is: - 1-the total size from the attributes in this class 2-the size responsible for answering this question, from which class this object has been created, this part is called the lookup table.

Also, we have objects called Immutable objects, which means that you can’t modify the contents of the object after construction. If you want to update an object you couldn't modify it and you should create a new one because that is easy for the processor to create a new object rather than modify it. for ex: - String

String pool: - String objects that are created without using the “new” keyword are said to belong to the “String Pool”.

Threads

Thread is a single sequential execution path in a program, used when we need to execute two or more programs segments concurrently(multitasking).

In Java, we have for every program at least three threads, two are called by the system and the other is the main thread

The system threads are: - 1-Garbage Collection Thread: - responsible for removing any variable or reference after finishing using it.

2-Event Dispatcher Thread: -?event dispatching thread?(EDT) is a background?thread used in Java to process events from the Abstract Window Toolkit

Class Thread has these methods: - start() - run() - sleep() - suspend()* - resume()* - stop()*