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javabytecodejasmin

Java bytecode with Jasmin: why is the message not printed on the screen?

I recently became interested in Java bytecode and I created the following Hello World program.

The "Hello World" is printed, however I can't figure out why "Creating awesome object" isn't printed. Can you help me figure out what I'm doing wrong?

.class public HelloWorld
.super java/lang/Object

.method public <init>()V
    .limit stack 2

    aload_0  ; push 'this' unto stack
    invokespecial java/lang/Object/<init>()V  ; invoke constructor

    getstatic java/lang/System/out Ljava/io/PrintStream;
    ldc "Creating awesome object!"
    invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V

    return
.end method

.method public static main([Ljava/lang/String;)V
    .limit stack 2

    getstatic java/lang/System/out Ljava/io/PrintStream;
    ldc "Hello world"
    invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V

    return
.end method
Solution

  • I don't know much about Java bytecode, but it seems to me you don't create an instance of HelloWorld in main. If you don't create an instance, the constructor does not get called, so there you have it. :)