javap Man page

javap Basic Tools javap

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.”“:()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.”“:()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

· javac

· javadoc

· javah

· jdb

· jdeps

JDK 8 8 August 2014 javap

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