如果我从类文件中删除超级构造函数调用会发生什么？

Question

当构造函数没有显式调用超类构造函数(或this())时,编译器就会插入super().

如果从类文件中删除此调用(编译后)会发生什么？

Answer 1

我亲自尝试过.

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

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

我编译它并invokespecial java/lang/Object/<init>()V使用类文件编辑器从构造函数中删除.

似乎JVM拒绝加载该类:

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)

我仍然不知道这是否是一个定义的行为.

编辑

根据Raedwald,我还必须改变堆栈操作.

所以我也删除aload_0了超级构造函数调用之前的内容.

现在我得到以下异常:

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)

这让我很好奇,所以我重新构建了构造函数指令:

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

哪个有效!