1.3 Understand What Is JDK JRE JVM And JIT

JDK(Java Development Kit) :

Java Developer Kit(JDK) contains tools needed to
develop the Java programs, and JRE to run

JDK is mainly targeted for java development.
i.e. You can create a Java file (with the help
of Java packages), compile a Java file and
run a java file.

JDK = JRE + Development Tools

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JRE (Java Runtime Environment) :

Java Runtime Environment(JRE) contains JVM, class
libraries, and other supporting files. It does not
contain any development tools such as
compiler, debugger, etc.

Actually, JVM runs the program, and it uses
the class libraries, and other supporting files
provided in JRE.
If you want to run any java program, you need
to have JRE installed in the system.

JRE = JVM + Java Package Classes +
Runtime Libraries

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JVM (Java Virtual Machine) :

JVM is an abstract machine. It is a specification
that provides a runtime environment in which
java bytecode can be executed.

JVM’s are available for many hardware and
software platforms. JVM is platform
dependent because of configuration of each
OS differs and this makes java Platform
Independent.

JVM performs the following main tasks:
- Loads code
- Verifies code
- Executes code

JIT (Just In Time Compiler):

JIT Compiler will be used to optimize the byte-code execution,
in such a way that java interpreter will not execute the repeated instruction
which will be in the loop for multiple time because JVM will already get to know that some instruction has to be executed multiple times so it stores the value in memory in its first execution and uses it from there.