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Javap tool in Java with examples
The javap tool is a useful means of retrieving the information of a specific class or interface. Through its capabilities of disassembling, the javap command—also known as the Java Disassembler—has been given the roles of providing users with comprehensive internal info. From the two options, -c or -verbose, each giving unique results, users are able to find themselves in the realms of byte code and byte code orchestration. If no options are used, javap runs through the public, protected and package fields and methods of inputted classes.
Syntax
javap [option] [classname]
When no options are used
Example
javap class_name
Output
C:\Users\Aashi>javap java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class<?> getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException; public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException;
public final void wait(long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
static {};
}
When options are used
Following is an explanation of each option and how to apply it −
-help or --help or -? −
This is used to print the help message for the javap command.
Example
javap -help
Output
C:\Users\Aashi>javap -help Usage: javap <options> <classes> where possible options include: -help --help -? Print this usage message -version Version information -V -verbose Print additional information -1 Print line number and local variable tables -public Show only public classes and members -protected Show protected/public classes and members -package Show package/protected/public classes and members (default) -p -private Show all classes and members -C Disassemble the code -S Print internal type signatures -sysinfo Show system info (path, size, date, MD5 hash) of class being processed -constants Show final constants -classpath <path> Specify where to find user class files -cp <path> Specify where to find user class files -bootclasspath <path> Override location of bootstrap class files
-version
This is used to print Version information of Java.
Example
javap -version
Output
C:\Users\Aashi>javap -version 1.8.0_151
-v or -verbose −
This is used to print additional information like stack size, number of locals and arguments for methods.
Example
javap -v class_name
Output
C:\Users\Aashi>javap -v java.lang.Object Classfile jar:file:/C:/Program%20Files/Java/jdk1.8.0_151/jre/lib/rt.jar! /java/lang/Object.class Last modified Sep 5, 2017; size 1497 bytes MD5 checksum 074ebc688a81170b8740f1158648a3c7 Compiled from "Object.java" public class java.lang.Object minor version: 0 major version: 52 flags: ACC_PUBLIC, ACC_SUPER Constant pool: #1 = Integer 999999 #2 - String #16 //@ #3 = String #38 //nanosecond timeout value out of range #4 = String #42 //timeout value is negative #5 - Utf8 ()I #6 = Utf8 ()Ljava/lang/Object; #7 - Utf8 ()Ljava/lang/String; #8 = Utf8 ()V #9 - Utf8 (I)Ljava/lang/String; #10 - Utf8 (J)V #11 = Utf8 (JI)V #12 - Utf8 (Ljava/lang/Object;)Z #13 = Utf8 (Ljava/lang/String;)V #14 - Utf8 <clinit> #15 = Utf8 <init> #16 - Utf8 @ #17 - Utf8 Code #18 = Utf8 Exceptions #19 - Utf8 Line Number Table #20 = Utf8 Signature #21- Utf8 Source File #22 = Utf8 StackMapTable #23 Utf8 Append #24 Utf8 Clone #25 = Utf8 Equals #26 Utf8 finalize #27 = Utf8 getClass #28 Utf8 getName #29 - Utf8 hashCode #30 = Utf8 java/lang/Class #31 - Utf8 java/lang/CloneNotSupportedException #32 = Utf8 java/lang/IllegalArgumentException #33 - Utf8 Java/lang/Integer #34 Utf8 java/lang/InterruptedException
-l −
This is used to print line numbers and local variables tables.
Example
javap -l class_name
Output
C:\Users\Aashi>javap -1 java.lang.Object
Compiled from "Object.java”
public class java.lang.Object {
public java.lang.Object();
LineNumberTable:
line 37: 0
public final native java.lang.Class<?> getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
LineNumberTable:
line 149: 0
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
LineNumberTable:
line 236: 0
public final native void notify();
public final native void notifyAll();
public final native void wait(long) throws Java.lang.InterruptedException;
public final void wait(long, int) throws java.lang.InterruptedException;
LineNumberTable:
line 447: 0
line 448: 6
line 451: 16
line 452: 26
line 456: 36
line 457: 40
line 460: 44
line 461: 49
public final void wait() throws java.lang.InterruptedException;
LineNumberTable:
line 502:0
line 503: 5
protected void finalize() throws java.lang.Throwable;
}
-public
This is used to print only public classes and members.
Example
javap -public class_name
Output
C:\Users\Aashi>javap -public java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class<?> getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException; public final void wait (long, int) throws java.lang.InterruptedException; public final void wait() throws java.lang.InterruptedException;
}
-protected
This is used to print protected/public classes and members.
Example
javap -protected class_name
Output
C:\Users\Aashi>javap -protected java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class<?> getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait(long) throws java.lang.InterruptedException;
public final void wait (long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
}
-package
This is used to print package/protected/public classes and members (default).
Example
javap -package class_name
Output
C:\Users\Aashi>javap -package java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class<?> getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException;
public final void wait (long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
static {};
}
-c
This is used to print disassembled code.
Example
javap -c class_name
Output
C:\Users\Aashi>javap -c java.lang.Object Compiled from "Object.java" public class java.lang.Object (public java.lang.Object(); Code: 0: return public final native java.lang.Class<?> getClass(); public native int hashCode(); public boolean equals(java.lang.Object); Code: 0: aload e 1: aload_1 2: 1f_acmpne 9 5:iconst_1 6: goto 10 9: iconst_0 10: ireturn protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException; public java.lang.String toString(); Code: 0: new #52 //class java/lang/StringBuilder 3: dup 4: invokespecial #74 //Method java/lang/StringBuilder."<init>": ()V 7: aload_e 8: invokevirtual #73 // Method getClass: ()Ljava/lang/Class; 11: invokevirtual #67 // Method java/lang/class.getName:()Ljava/lang/String; 14: invokevirtual #76 // Method java/lang/StringBuilder.append: (Ljava/lang/String;) Ljava/lang/StringBuilder; 17: 1dc #2 // String @ 19: invokevirtual #76 // Method java/lang/StringBuilder.append: (Ljava/lang/String;)Ljava/lang/StringBuilder; 22: aload_e 23: invokevirtual #78 // Method hashCode: ()I 26: invokestatic #69 // Method java/lang/Integer.toHexString: (I) Ljava/lang/String; 29: invokevirtual #76 // Method java/lang/StringBuilder.append: (Ljava/lang/String;) Ljava/lang/StringBuilder; 32: invokevirtual #75 // Method java/lang/StringBuilder.toString: ()Ljava/lang/String; 35: areturn public final native void notify();
-s −
This is used to print internal type signatures.
Example
javap -s class_name
Output
C:\Users\Aashi>javap -s java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
descriptor: ()V
public final native java.lang.Class<?> getClass();
descriptor: ()Ljava/lang/class;
public native int hashCode();
descriptor: ()I
public boolean equals(java.lang.Object);
descriptor: (Ljava/lang/Object;)Z
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
descriptor:()Ljava/lang/Object;
public java.lang.String toString();
descriptor: ()Ljava/lang/String;
public final native void notify();
descriptor: ()V
public final native void notifyAll();
descriptor: ()V
public final native void wait(long) throws java.lang.InterruptedException; descriptor: (J)V
public final void wait(long, int) throws java.lang.InterruptedException; descriptor: (JI)V
public final void wait() throws java.lang.InterruptedException;
descriptor: ()V
protected void finalize() throws java.lang.Throwable;
descriptor: ()V
static {};
descriptor: ()V
}
-sysinfo −
This is used to print system info (path, size, date, MD5 hash) of class being processed.
Example
javap -sysinfo class_name
Output
C:\Users\Aashi>javap -sysinfo java.lang.Object
Classfile jar:file:/C:/Program%20Files/Java/jdk1.8.0_151/jre/lib/rt.jar! /java/lang/Object.class
Last modified Sep 5, 2017; size 1497 bytes
MD5 checksum 074ebc688a81170b8740f1158648a3c7
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class<?> getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException;
public final void wait (long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
static {};
}
-constants −
This is used to print final constants of class.
Example
javap -constants class_name
Output
C:\Users\Aashi>javap -constants java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class<?> getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException;
public final void wait(long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
static {};
}
Conclusion
The javap tool is a multifaceted and tremendously potent tool for Java coders, rendering them the capacity to diagnose and debug class documents, evaluate fields and methods, and generate legible code from a class document's bytecode. This indispensable tool is suitable for Java developers of all skill levels, affording them the capability to extend their knowledge and troubleshoot their Java programs without difficulty. An irreplaceable possession for any aspiring coder, the javap tool is sure to help quickly enhance their programming aptitude. Additionally, its wide range of features can assist coders in refining their practices, providing them a competitive edge when it comes to building Java applications.
Updated on: 01-Aug-2023
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