What happens if I remove the super constructor call from class file?

Question

When a constructor doesn't have a explicit call of the super class constructor (or this()) then the compiler inserts super().

What would happen if this call was removed from the class file (after compilation)?

Answer 1

I tried it myself.

class Test
{
    public Test()
    {
        System.out.println("Hello World");
    }

    public static void main(String[] args)
    {
        new Test()
    }
}

I compiled it and removed invokespecial java/lang/Object/<init>()V from the constructor with a class file editor.

It seems like the JVM refuses to load the class:

Exception in thread "main" java.lang.VerifyError: Operand stack overflow
Exception Details:
  Location:
    Test.<init>()V @4: ldc
  Reason:
    Exceeded max stack size.
  Current Frame:
    bci: @4
    flags: { flagThisUninit }
    locals: { uninitializedThis }
    stack: { uninitializedThis, 'java/io/PrintStream' }
  Bytecode:
    0000000: 2ab2 0002 1203 b600 04b1

        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
        at java.lang.Class.getMethod0(Unknown Source)
        at java.lang.Class.getMethod(Unknown Source)
        at sun.launcher.LauncherHelper.validateMainClass(Unknown Source)
        at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)

I still don't know if that is a defined behaviour.

EDIT

According to Raedwald I also have to alter the stack manipulation.

So I also removed aload_0 which was before the super constructor call.

Now I get the following exception:

Exception in thread "main" java.lang.VerifyError: Constructor must call super()
or this() before return
    Exception Details:
  Location:
    org/exolin/geno/Test.<init>()V @8: return
  Reason:
    Error exists in the bytecode
  Bytecode:
    0000000: b200 0212 03b6 0004 b1

        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
        at java.lang.Class.getMethod0(Unknown Source)
        at java.lang.Class.getMethod(Unknown Source)
        at sun.launcher.LauncherHelper.validateMainClass(Unknown Source)
        at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)

This made me curious so I reordered the constructor instructions to:

getstatic java/lang/System/out Ljava/io/PrintStream;
ldc "Message"
invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V
aload_0
invokespecial java/lang/Object/<init>()V
return

Which worked!