javap

javap − The Java Class File Disassembler

Disassembles class files.

javap [ options ] class. . .

The javap command disassembles a class file. Its output depends on the options used. If no options are used, javap prints out the package, protected, and public fields and methods of the classes passed to it. javap prints its output to stdout. For example, compile the following class declaration:

import java.awt.*;
import java.applet.*;

public class DocFooter extends Applet {
        String date;
        String email;

       public void init() {
                resize(500,100);
                date = getParameter("LAST_UPDATED");
                email = getParameter("EMAIL");
        }

       public void paint(Graphics g) {
                g.drawString(date + " by ",100, 15);
                g.drawString(email,290,15);
        }
}

The output from javap DocFooter yields:

Compiled from DocFooter.java
public class DocFooter extends java.applet.Applet {
    java.lang.String date;
    java.lang.String email;
    public DocFooter();
    public void init();
    public void paint(java.awt.Graphics);
}

The output from javap −c DocFooter yields:

Compiled from DocFooter.java
public class DocFooter extends java.applet.Applet {
    java.lang.String date;
    java.lang.String email;
    public DocFooter();
    public void init();
    public void paint(java.awt.Graphics);
}

Method DocFooter()
   0 aload_0
   1 invokespecial #1 <Method java.applet.Applet()>
   4 return

Method void init()
   0 aload_0
   1 sipush 500
   4 bipush 100
   6 invokevirtual #2 <Method void resize(int, int)>
   9 aload_0
  10 aload_0
  11 ldc #3 <String "LAST_UPDATED">
  13 invokevirtual #4 <Method java.lang.String getParameter(java.lang.String)>
  16 putfield #5 <Field java.lang.String date>
  19 aload_0
  20 aload_0
  21 ldc #6 <String "EMAIL">
  23 invokevirtual #4 <Method java.lang.String getParameter(java.lang.String)>
  26 putfield #7 <Field java.lang.String email>
  29 return

Method void paint(java.awt.Graphics)
   0 aload_1
   1 new #8 <Class java.lang.StringBuffer>
   4 dup
   5 invokespecial #9 <Method java.lang.StringBuffer()>
   8 aload_0
   9 getfield #5 <Field java.lang.String date>
  12 invokevirtual #10 <Method java.lang.StringBuffer append(java.lang.String)>
  15 ldc #11 <String " by ">
  17 invokevirtual #10 <Method java.lang.StringBuffer append(java.lang.String)>
  20 invokevirtual #12 <Method java.lang.String toString()>
  23 bipush 100
  25 bipush 15
  27 invokevirtual #13 <Method void drawString(java.lang.String, int, int)>
  30 aload_1
  31 aload_0
  32 getfield #7 <Field java.lang.String email>
  35 sipush 290
  38 bipush 15
  40 invokevirtual #13 <Method void drawString(java.lang.String, int, int)>
  43 return

−help

Prints out help message for javap.

−l

Prints out line and local variable tables.

−b

Ensures backward compatibility with javap in JDK 1.1.

−public

Shows only public classes and members.

−protected

Shows only protected and public classes and members.

−package

Shows only package, protected, and public classes and members. This is the default.

−private

Shows all classes and members.

−Jflag

Pass flag directly to the runtime system. Some examples:

javap −J−version
javap −J−Djava.security.manager −J−Djava.security.policy=MyPolicy MyClassName

−s

Prints internal type signatures.

−c

Prints out disassembled code, i.e., the instructions that comprise the Java bytecodes, for each of the methods in the class. These are documented in the Java Virtual Machine Specification @

http://java.sun.com/docs/books/vmspec/.

−verbose

Prints stack size, number of locals and args for methods.

−classpath path

Specifies the path javap uses to look up classes. Overrides the default or the CLASSPATH environment variable if it is set. Directories are separated by colons. Thus the general format for path is:

   .:<your_path>

For example:

−bootclasspath path

Specifies path from which to load bootstrap classes. By default, the bootstrap classes are the classes implementing the core Java platform located in jre/lib/rt.jar and several other jar files.

−extdirs dirs

Overrides location at which installed extensions are searched for. The default location for extensions is the value of java.ext.dirs.

CLASSPATH

Used to provide the system a path to user−defined classes. Directories are separated by colons, for example, For example:

javac, java, jdb, javah, javadoc