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javap

WIP

Disassembles .class compiled files so you can see their internal structure.

TODO mnemonic for the p in the name? Because it Prints to stdout?

Print a human readable version of the JVM instructions:

javap -c -constants -private -verbose HelloWorld

Sample output for a hello world program:

Classfile /home/ciro/bak/git/java-cheat/target/HelloWorld.class
Last modified Mar 18, 2015; size 426 bytes
MD5 checksum 7a3ee81e13319873b7ac05812c3e5571
Compiled from "HelloWorld.java"
public class HelloWorld
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref          #6.#15         // java/lang/Object."<init>":()V
#2 = Fieldref           #16.#17        // java/lang/System.out:Ljava/io/PrintStream;
#3 = String             #18            // Hello world!
#4 = Methodref          #19.#20        // java/io/PrintStream.println:(Ljava/lang/String;)V
#5 = Class              #21            // HelloWorld
#6 = Class              #22            // java/lang/Object
#7 = Utf8               <init>
#8 = Utf8               ()V
#9 = Utf8               Code
#10 = Utf8               LineNumberTable
#11 = Utf8               main
#12 = Utf8               ([Ljava/lang/String;)V
#13 = Utf8               SourceFile
#14 = Utf8               HelloWorld.java
#15 = NameAndType        #7:#8          // "<init>":()V
#16 = Class              #23            // java/lang/System
#17 = NameAndType        #24:#25        // out:Ljava/io/PrintStream;
#18 = Utf8               Hello world!
#19 = Class              #26            // java/io/PrintStream
#20 = NameAndType        #27:#28        // println:(Ljava/lang/String;)V
#21 = Utf8               HelloWorld
#22 = Utf8               java/lang/Object
#23 = Utf8               java/lang/System
#24 = Utf8               out
#25 = Utf8               Ljava/io/PrintStream;
#26 = Utf8               java/io/PrintStream
#27 = Utf8               println
#28 = Utf8               (Ljava/lang/String;)V
{
public HelloWorld();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
    stack=1, locals=1, args_size=1
        0: aload_0
        1: invokespecial #1                  // Method java/lang/Object."<init>":()V
        4: return
    LineNumberTable:
        line 1: 0

public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
    stack=2, locals=1, args_size=1
        0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
        3: ldc           #3                  // String Hello world!
        5: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        8: return
    LineNumberTable:
        line 3: 0
        line 4: 8
}
SourceFile: "HelloWorld.java"

TODO understand.