How JVM plays an important in the execution of

Java program

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To write a program we need-

1) Editor– To type a program into, for example notepad,notepad++ etc.

2) Compiler – To convert high level language program into machine code

3) Linker – To combine different program files reference in your main program together.

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4) Loader – To load the files from the secondary storage device like Hard Disk, Flash Drive , CD into RAM for execution.The loading is automatically done when we execute our code.

5) Execution – Actual execution of the program which is handled by OS(Operating System) & processor.

Java CodeCompilation & execution

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[1] Once we write a program , we have to save with the class name.java.[2]Once we execute a program .java file converts into .class file[3]JVM convert the .class file into machine code.[4]JVM divide the memory into stack and memory memory.[5]Then JVM call the class loader , class loader go back to the main class and find the all stack members and load into heap memory.

[5]Again control go back to the JVM , it loads the all static members into stack.[6]Then it try to identifies the main method and start the execution.[7]If main method is not there , then it will through the error and execution will stop.[8]Once execution done JVM call garbage collector to clear the memory.

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What is JVM

JVM stands for Java Virtual Machine.It is the engine that executes the java code.

It converts byte code to machine code

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1) Java compiler produces code for a Virtual Machine.2) JVM compiled java code into bytecode. This bytecode gets interpreted on machines3) Between host system and Java source, Bytecode is an intermediate language.4) JVM is responsible for allocating a memory space.

Working of JVM

The JVM performs following works :1)Loads the java code2)Verifies the code3)Executes the code4)Provides runtime environment

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Java is both Compiled & Interpreted

Language

Compiler :

A compiler is a program which converts a program from one level of language to another. Example conversion of C++ program into machine code. The java compiler converts high level java code into bytecode .

Interpreter :A interpreter is a program which converts a program at one level to another programming language at the same level. In Java , the JVM converts the bytecode into the native machine code

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ArchitectureOf

Java Virtual Machine

[1] Classloader:Classloader is a subsystem of JVM which is used to load the class files into the memory.

[2] Class Area(Method Area):Class Area stores per-class structures such as the runtime constant pool, fields and methods, code for methods.

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[3] Stack:Java Stack stores frames.It holds local variables and partial results, and plays a part in method invocation and return.Each thread has a private JVM stack, created at the same time as thread.

[4] Native Method Stack:Native Method Stack contains all the native methods used in the application.

[5] Heap:Heap is the runtime data area in which objects are allocated and stored.

[6] Program Counter Register:PC (program counter) register contains the address of the Java virtual machine instruction currently being executed.

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[7] Execution Engine :Execution Engine contains :i) A virtual processorii) Interpreter: Read bytecode stream then execute the instructions.iii) Just-In-Time(JIT) compiler: It is used to improve the performance.JIT compiles parts of the byte code that have similar functionality at the same time, and hence reduces the amount of time needed for compilation.

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