JDK JRE JVM

JDK JRE JVM

Java software contains three major parts.

before work with Java we must aware JDK, JRE, JVM

 

Java Development Kit (JDK):

JDK allows users to develop Java based applications that will be executed and run by JVM/JRE.

inside JDK it contains JRE and development tools (Compiler, Debugger…etc.).

The Java compiler translates the source code (high level language) to byte code (not machine level language).

Note: here byte code is generated by Java compiler. 

after compiling separate ".class" file will be generated, this byte code can understand by JVM only.

 

Java Runtime Environment (JRE):

JRE is a set of software tools that provides minimum requirements for executing Java applications,

it contains Java classes and JVM. 

inside JRE predefined libraries are available by using these library files (pre developed Java classes) lot of complexity will be reduced for developer.

JRE consist of 

• deployment technologies (Java web).

• user interface tool kit (AWT, Swing, print service, sound, input/output).

• integration libraries (JNDI, JDBC, RMI).

• beans, JNI, networking, xml, serialization.

• lang & util base libraries: collection, logging etc.!. 

some of the pre developed library files are:

SQL, Lang, IO …etc.!

Ex: we are calling println() method to print the values.

this print() method available at PrintStream class, this class is available under IO Package.

 

Java Virtual Machine (JVM): 

JVM is a virtual machine it does not physically exist.

It resides inside computer.

Java virtual machine is virtually created memory inside a computer memory.

Java is platform independent but JVM not. 

1.compiler is responsible to convert Java source code into bytecode and storing these bytecodes in a separate file with extension “.class”.

2. JVM is responsible to execute these bytecodes. JVM executes those bytecodes by converting them into the machine level language of current OS.

3. JVM is OS dependent, because it takes Java bytecodes and generates OS dependent machine language.