manpagez: man pages & more
man javap(1)
Home | html | info | man
javap(1)                         JDK Commands                         javap(1)




NAME

       javap - disassemble one or more class files


SYNOPSIS

       javap [options] classes...

       options
              Specifies the command-line options.  See Options for javap.

       classes
              Specifies  one  or  more  classes separated by spaces to be pro-
              cessed for annotations.  You can specify a  class  that  can  be
              found  in  the class path by its file name, URL, or by its fully
              qualified class name.

              Examples:

                     path/to/MyClass.class

                     jar:file:///path/to/MyJar.jar!/mypkg/MyClass.class

                     java.lang.Object


DESCRIPTION

       The javap command disassembles one or more class files.  The output de-
       pends on the options used.  When no options are used, the javap command
       prints the protected and public fields,  and  methods  of  the  classes
       passed to it.

       The  javap  command isn't multirelease JAR aware.  Using the class path
       form of the command results in viewing the base entry in all JAR files,
       multirelease  or  not.  Using the URL form, you can use the URL form of
       an argument to specify a specific version of a class  to  be  disassem-
       bled.

       The javap command prints its output to stdout.

       Note:

       In  tools  that support -- style options, the GNU-style options can use
       the equal sign (=) instead of a white space to separate the name of  an
       option from its value.


OPTIONS FOR JAVAP

       --help, -help , -h, or -?
              Prints a help message for the javap command.

       -version
              Prints release information.

       -verbose or -v
              Prints additional information about the selected class.

       -l     Prints line and local variable tables.

       -public
              Shows only public classes and members.

       -protected
              Shows only protected and public classes and members.

       -package
              Shows package/protected/public classes and members (default).

       -private or -p
              Shows all classes and members.

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

       -s     Prints internal type signatures.

       -sysinfo
              Shows system information (path, size, date, SHA-256 hash) of the
              class being processed.

       -constants
              Shows static final constants.

       --module module or -m module
              Specifies the module containing classes to be disassembled.

       --module-path path
              Specifies where to find application modules.

       --system jdk
              Specifies where to find system modules.

       --class-path path, -classpath path, or -cp path
              Specifies the path that the javap  command  uses  to  find  user
              class files.  It overrides the default or the CLASSPATH environ-
              ment variable when it's set.

       -bootclasspath path
              Overrides the location of bootstrap class files.

       --multi-release version
              Specifies the version to select in multi-release JAR files.

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

                     javap -J-version

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

              See Overview of Java Options in java.


JAVAP EXAMPLE

       Compile the following HelloWorldFrame class:

              import java.awt.Graphics;

              import javax.swing.JFrame;
              import javax.swing.JPanel;

              public class HelloWorldFrame extends JFrame {

                 String message = "Hello World!";

                 public HelloWorldFrame(){
                      setContentPane(new JPanel(){
                          @Override
                          protected void paintComponent(Graphics g) {
                              g.drawString(message, 15, 30);
                          }
                      });
                      setSize(100, 100);
                  }
                  public static void main(String[] args) {
                      HelloWorldFrame frame = new HelloWorldFrame();
                      frame.setVisible(true);

                  }

              }

       The output from the javap HelloWorldFrame.class command yields the fol-
       lowing:

              Compiled from "HelloWorldFrame.java"
              public class HelloWorldFrame extends javax.swing.JFrame {
                java.lang.String message;
                public HelloWorldFrame();
                public static void main(java.lang.String[]);
              }

       The  output  from the javap -c HelloWorldFrame.class command yields the
       following:

              Compiled from "HelloWorldFrame.java"
              public class HelloWorldFrame extends javax.swing.JFrame {
                java.lang.String message;

                public HelloWorldFrame();
                  Code:
                     0: aload_0
                     1: invokespecial #1        // Method javax/swing/JFrame."<init>":()V
                     4: aload_0
                     5: ldc           #2        // String Hello World!
                     7: putfield      #3        // Field message:Ljava/lang/String;
                    10: aload_0
                    11: new           #4        // class HelloWorldFrame$1
                    14: dup
                    15: aload_0
                    16: invokespecial #5        // Method HelloWorldFrame$1."<init>":(LHelloWorldFrame;)V
                    19: invokevirtual #6        // Method setContentPane:(Ljava/awt/Container;)V
                    22: aload_0
                    23: bipush        100
                    25: bipush        100
                    27: invokevirtual #7        // Method setSize:(II)V
                    30: return

                public static void main(java.lang.String[]);
                  Code:
                     0: new           #8        // class HelloWorldFrame
                     3: dup
                     4: invokespecial #9        // Method "<init>":()V
                     7: astore_1
                     8: aload_1
                     9: iconst_1
                    10: invokevirtual #10       // Method setVisible:(Z)V
                    13: return
              }



JDK 15                               2020                             javap(1)

openjdk 15.0.2 - Generated Tue Feb 23 15:54:58 CST 2021
© manpagez.com 2000-2021
Individual documents may contain additional copyright information.