JRE and JDK

Difference between JVM, JDK, and JRE

• JVM - Java Virtual Machine is a virtual machine which runs programs which are compiled to bytecodes. The JVM is detailed by a specification that formally describes what is required in a JVM implementation. Having a specification ensures interoperability of Java programs across different implementations so that program authors using the Java Development Kit (JDK) need not worry about traits of the underlying hardware platform.
• JDK- JDK is a wrapper around the JRE and additionally contains the compiler, interpreter, debugger and other tools. It provides users with features to run as well as develop Java programs.
• JRE- JRE is made up of class libraries, JVM and supporting files

Conversion process- [JAVA .class file into back to SOURCE code]

Step 1: Download JAD tool from https://bit.ly/2XuRzT5

Step 2: Extract the zip file and get jad.exe.

Step 3: Create a .java file (DecompilerDemo.java) in the same folder in which you have extracted the zip file.

Step 4: Compile and run the .java file. It will generate a .class file in the respective folder.

Step 5: Now move the .class file and jad application to another folder.

Step 6: Type the command: jad DecompilerDemo

Above command generates a .jad file in the respective folder.

Step 7: Type the command: jad ?s java DecompilerDemo

It generates the .java file in the same folder.

Open the DecompilerDemo.java we get the following code:

JAVA class Decompiler

Options

With javap command, many options are available. Some of them are:

• -c: It prints disassembled code.
• -p: It shows all classes and members.
• -s: It prints internal type signatures.
• -constants: It shows static final constants.