Introduction:

As we know computer understands only 0's and 1's we need to give instructions in the

same manner.

Programming Languages are used to instruct computers understand the instructions

provided by human.

File Structures:

We write instructions in different file structures.

• .java file in case of java.

• For other like C we use .c file and so on.

• In C and C++ we write the code and give the code to compiler.

• Here code is compiled by compiler to executable machine code.

• But in case of java its converted into byte code and then to machine code so java is

platform independent and can be run from anywhere.

• In case of python interpreter compiles the code.

Interpreter:

Compiles the code line by line.

Compiler:

Take the code and convert it to 0's and 1's. * But in Java we send the code to compiler and the entire file is sent to byte code which is

stored in .class file.

We had byte code because we cant directly run in the system so we use JVM.

JVM means java virtual machine.

The java execution is shown in the below illustrated image.

There will be many confusions regarding the terms so lets have a small discussion on the topics

1. Platform independence:

-Platform independence means the byte code can run on all operating systems.

• While compiling C and C++ file we get .exe (executable) file which is platform dependent.

• Platform dependent means works only on one platform.

• In java it creates byte code where we can use the file in any file or platforms.

• In java byte code is created using JVM converts to machine code.

• If we have JVM we can run any of files of java but JVM is platform dependent.

• Byte code is platform independent.

Architecture of JAVA

1. JDK-Java Development Kit

2. JRE - Java Runtime Environment

3. JVM -Java virtual Machine

4. JIT-Just in time compiler

1. JDK

A package or set of files which provides tools to run a program.

1. Development tools - provides and environment to run a program

2. JRE - to execute the program

3. Consists of compiler - javac

4. Archiver - jar

5. docs generator - javadoc

6.interpreter / loader

2. JRE -Java Runtime Environment:

installation package that provides an environment to run a program

It consists of

1. Deployment technologies

2. User interface tool kits

3. Integration libraries

4. Base libraries

3. JVM -Java Virtual Machine:

After the .class file

class loader loads all classes needed to execute the program

JVM sends code to byte code verifier and does code formatting.

Java doesn't have pointers.

Compile time

• .java file compiles to .class file

javac-- java compilation

class Loader

two operations in class loader

1. Loading

   1. Reads .class file and creates binary data

2. An object of this class is created in heap memory

Linking:

Linking contains three steps

1. Verifies the .class file

2. allocates memory for class variables and values

3. replace symbolic references with actual values.

JVM has stack and heap memory allocations.

All values will be assigned to their respective values.

Static means the values are not changed.

JVM execution

Interpreter:

1. line by line execution.
2. byte file is executed line by line.
3. when one method is called many times it will be used again and again.
4. byte code is converted to machine code again and again.

So to solve repeating of executions again and again we use JIT.

4. JIT -Just in time

JIT provides machine code so that repetition of interpretation is not required this allows making execution faster

Garbage collection is also used here Garbage collections in short refers to removal of unused variables and values and only uses the declared variables which saves memory

The process of execution can be given as following steps

Java source code - .class file is sent to JDK where it converts to byte code and JVM checks and converts to machine code and JRE runs and checks the packages required to run a program and output is displayed

JRE and JRM are interconnected to each other to perform code compilation and providing required files.

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