Java: if-return-if-return vs if-return-elseif-return

Question

Asked an unrelated question where I had code like this:

public boolean equals(Object obj) {     if (this == obj)         return true;      if (obj == null)         return false;      if (getClass() != obj.getClass())         return false;      // Check property values } 

I got a comment which claimed that this was not optimal, and that it instead (if I understood correctly) should do this:

public boolean equals(Object obj) {     if (this == obj)         return true;      else if (obj == null)         return false;      else if (getClass() != obj.getClass())         return false;      // Check property values } 

Because of the return statements, I can't really see why any of them should be more efficient or faster than the other. Given a certain object, both methods would have to do an equal number of checks as far as I can see. And because of the return statements, no extra code would run in any of them.

Am I missing something here? Is there something to it? Are there some compiler optimizations or something going on or whatever?

I know this is micro optimization and I will most likely stick with the first either way, since I think it looks cleaner with all the ifs on the same position. But I can't help it; I'm curious!

Answer 1

The generated byte code is identical for those two cases, so it's purely a matter of style.

I produced two methods e1 and e2 and both produced this byte code (read using javap -v):

 public boolean e1(java.lang.Object);   Code:    Stack=2, Locals=2, Args_size=2    0:   aload_0    1:   aload_1    2:   if_acmpne   7    5:   iconst_1    6:   ireturn    7:   aload_1    8:   ifnonnull   13    11:  iconst_0    12:  ireturn    13:  aload_0    14:  invokevirtual   #25; //Method java/lang/Object.getClass:()Ljava/lang/Class;    17:  aload_1    18:  invokevirtual   #25; //Method java/lang/Object.getClass:()Ljava/lang/Class;    21:  if_acmpeq   26    24:  iconst_0    25:  ireturn 

I left out the code I put after that to make it compile.