javap

Disassembles one or more class files.

Synopsis

javap [options] classfile...
  • 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
  • -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

The output from the javap DocFooter.class command yields the following:

Compiled from "DocFooter.java"
public class t5750.javap.DocFooter extends java.applet.Applet {
  java.lang.String date;
  java.lang.String email;
  public t5750.javap.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 t5750.javap.DocFooter extends java.applet.Applet {
  java.lang.String date;

  java.lang.String email;

  public t5750.javap.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
}

References