Introduction To Javap Tool In Java

Introduction

In this article we discuss the javap command in Java and how to create your own javap command.

Javap command in Java

The javap command disassembles compiled Java files. The javap command displays information about the variables, constructors and methods present in a class file. This may be helpful when the original source code is no longer available on a system.

The output of javap commands depend on the options used. If you do not specify an option then it simply prints out the package, public fields & protected methods of the class.

Example

Developing a program that just works the same as the javap command

The following public methods can be used for displaying metadata of a class.

Method[] getDeclaredMethods() thows SecurityException

returns an array of method objects reflecting all the methods declared by the class or interface represented by this Class object.

Field[] getDeclaredFields() throws SecurityException

returns an array of filed objects reflecting all the fields declared by the class or interface represented by this Class object.

Constructor[] getDeclaredConstructor() throws SecurityException

return an array of Constructor objects reflecting all the constructors declared by the class represented by the Class object.

Example

import java.lang.reflect.*;

public class JavapEx

  {

    public static void main(String args[]) throws Exception

      {

        Class cls=Class.forName(args[0]);

        System.out.println("Fields are...........");

        Field fld[]=cls.getDeclaredFields();

        for(int i=0;i<fld.length;i++)

        System.out.println(fld[i]);

        System.out.println("Constructors are.....");

        Constructor con[]=cls.getDeclaredConstructors();

        for(int i=0;i<con.length;i++)

        System.out.println(con[i]);

        System.out.println("Methods are.........");

        Method mthd[]=cls.getDeclaredMethods();

        for(int i=0;i<mthd.length;i++)

        System.out.println(mthd[i]);

      }

  }

Output