I am wondering why the Exception in the following bytecode (used to throw an Exception) is duplicated.
NEW java/lang/IllegalArgumentException
DUP
INVOKESPECIAL java/lang/IllegalArgumentException <init> ()V
ATHROW
I'll analyze this line by line where [] = new stack after that op is used:
IllegalArgumentException
onto the stack [SomeIllegalArgumentException]
In byte code, an object is first created by class, and then a constructor is called on that object. The signature of a constructor ends with V
for void
as it does return anything. This means a copy of the original reference to the object must be kept on the stack (or in a variable) so it can be thrown after the constructor is called.
BTW The internal name for a constructor is <init>
and the internal name for a static initialiser code is <clinit>
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