Inside JAVA – Part 1

Feature of JAVA programming language:-

From above we get,

JAVA is simple, because, JAVA removes the virtual, friend, pointer concepts which are from C and C++.
We can write a JAVA code anywhere and run it. So, it is called as WORA means Write Once Run Anywhere.
JAVA is Robust, because, it has a strong exception handling.
JAVA provides all functionality at the runtime. So, it is dynamic.

Java uses the following features to fulfill the previously listed goals:

The Java Virtual Machine:-

The JVM is an imaginary machine that is implemented it in a software on a real machine.
The Java Virtual Machine provides hardware platform specifications to which you compile all the java technology codes.
This specification enables the java to be platform independent, because the compilation is done for a generic machine, known as JVM.
Compiler takes the java source code and generates a bytecode.
Bytecodes are the machine code instructions for the JVM.
Bytecode are stored in a .class file.
The JVM specification provides a concrete definitions for the implementation of:

1) Instruction set

2) Register set

3) CPU

4) Garbage collected heap

5) A memory area

6) Fatal error reporting mechanism

7) High precision timing support

Garbage collection:-

When we run a java program memory for that program is allocated inside the memory of the JVM.
When JVM runs 1^st time it sends the requirement to the OS for particular amount of a memory.
OS allocates a memory to the JVM and allocated memory is managed by the JVM.
Managing this memory means allocating the memory for particular reference or de-allocating the memory which is not referenced.
And this memory is called as managed memory.
When OS allocates a memory for the JVM. The JVM initialized that memory to 0 that’s why each and every member is initialized with 0 by default.
When we allocate a memory for a java program the reference of that memory is kept by the JVM.
If that reference is pointing such a memory which is not in used by any other program that memory is considered as unreferenced memory.
In the JVM garbage collector is a thread which scan a memory of JVM periodically.
While scanning if it found some memory which is unreferenced that memory is collected by the garbage collector.
For de-allocating memory garbage collector uses reference count concept similar as OS.
According to above description we can predict that we cannot decide the execution of a destructor, because, the garbage collector is called periodically.
Means we cannot predict when the finalize method is called.

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