Question

I’ve recently installed bytecode outline Eclipse plugin and discovered that my Test class

public class Test {
}

calls java.lang.Object’s constructor

public class Test {
  public <init>()V
   L0
    LINENUMBER 15 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init>()V
    RETURN
   L1
    LOCALVARIABLE this LTest; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1
}

INVOKESPECIAL java/lang/Object.<init>()V means calling java.lang.Object’s constructor

Does it make any sense? Judging by java.lang.Object bytecode

  public <init>()V
   L0
    LINENUMBER 37 L0
    RETURN
    MAXSTACK = 0
    MAXLOCALS = 1

it’s doing nothing. Just returns.

Answer 1

It has to in order to satisfy section 4.9.2 of the JVM specification on structural constraints:

Each instance initialization method (§2.9), except for the instance initialization method derived from the constructor of class Object, must call either another instance initialization method of this or an instance initialization method of its direct superclass super before its instance members are accessed.

Now the rule could be relaxed for classes which are direct subclasses of Object – but I doubt that it would have any benefit, and would be inelegant (IMO). What if the Object constructor did perform some initialization in the future? Would you really want a spec which allowed you to bypass it?