javap-java-1.8.0-openjdk-1.8.0.121-0.b13.el7_3.x86_64 (1) Linux Manual Page

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)

• javah(1)

• jdb(1)

• jdeps(1)