javap(1)

NAME
javap - Disassembles one or more class files.

SYNOPSIS

    javap [options] classfile...

options
    The command-line options. See Options.

classfile
    One or more classes separated by spaces to be processed for annotations such as DocFooter.class. You can specify a class that can be found in the class path, by its file name or with a URL such as file:///home/user/myproject/src/DocFooter.class.

DESCRIPTION

The javap command disassembles one or more class files. The output depends on the options used. When no options are used, then the javap command prints the package, protected and public fields, and methods of the classes passed to it. The javap command prints its output to stdout.

OPTIONS

-help
--help
-?
    Prints a help message for the javap command.

-version
    Prints release information.

-l
    Prints line and local variable tables.

-public
    Shows only public classes and members.

-protected
    Shows only protected and public classes and members.

-private
-p
    Shows all classes and members.

-Joption
    Passes the specified option to the JVM. For example:

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

    For more information about JVM options, see the command documentation.

-s
    Prints internal type signatures.

-sysinfo
    Shows system information (path, size, date, MD5 hash) of the class being processed.

-constants
    Shows static final constants.

-c
    Prints disassembled code, for example, the instructions that comprise the Java bytecodes, for each of the methods in the class.

-verbose
    Prints stack size, number of locals and arguments for methods.

-classpath path
    Specifies the path the javap command uses to look up classes. Overrides the default or the CLASSPATH environment variable when it is set.

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

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

EXAMPLE

Compile the following DocFooter class:

    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 the javap DocFooter.class command yields the following:

    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.class command yields the following:

    Compiled from "DocFooter.java"
    public class DocFooter extends java.applet.Applet {
      java.lang.String date;
      java.lang.String email;

      public DocFooter();
        Code:
           0: aload_0
           1: invokespecial #1                  // Method
    java/applet/Applet."<init>":()V
           4: return

      public void init();
        Code:
           0: aload_0
           1: sipush        500
           4: bipush        100
           6: invokevirtual #2                  // Method resize:(II)V
           9: aload_0
          10: aload_0
          11: ldc           #3                  // String LAST_UPDATED
          13: invokevirtual #4                  // Method
     getParameter:(Ljava/lang/String;)Ljava/lang/String;
          16: putfield      #5                  // Field date:Ljava/lang/String;
          19: aload_0
          20: aload_0
          21: ldc           #6                  // String EMAIL
          23: invokevirtual #4                  // Method
     getParameter:(Ljava/lang/String;)Ljava/lang/String;
          26: putfield      #7                  // Field email:Ljava/lang/String;
          29: return

      public void paint(java.awt.Graphics);
        Code:
           0: aload_1
           1: new           #8                  // class java/lang/StringBuilder
           4: dup
           5: invokespecial #9                  // Method
     java/lang/StringBuilder."<init>":()V
           8: aload_0
           9: getfield      #5                  // Field date:Ljava/lang/String;
          12: invokevirtual #10                 // Method
     java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
          15: ldc           #11                 // String  by
          17: invokevirtual #10                 // Method
     java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
          20: invokevirtual #12                 // Method
     java/lang/StringBuilder.toString:()Ljava/lang/String;
          23: bipush        100
          25: bipush        15
          27: invokevirtual #13                 // Method
     java/awt/Graphics.drawString:(Ljava/lang/String;II)V
          30: aload_1
          31: aload_0
          32: getfield      #7                  // Field email:Ljava/lang/String;
          35: sipush        290
          38: bipush        15
          40: invokevirtual #13                 // Method
    java/awt/Graphics.drawString:(Ljava/lang/String;II)V
          43: return
    }

SEE ALSO

    • java(1)

    • javac(1)

    • javadoc(1)

    • jdb(1)

    • jdeps(1)