Question

I’m curious to know if either of these two Java method invocations will behave differently at all in terms of processor time, memory allocation and/or garbage collection.

SomeObject myObj = new SomeObject();
myObj.doSomething();

vs.

new SomeObject().doSomething();

Answer 1

Looking at the generated bytecode:

// code 1
new SomeObject().doSomething();

// bytecode 1
   0:   new #2; //class SomeObject
   3:   dup
   4:   invokespecial   #3; //Method SomeObject."<init>":()V
   7:   invokevirtual   #4; //Method SomeObject.doSomething:()V
   10:  return

You can clearly see that this one has two more instructions:

// code 2
SomeObject myObj = new SomeObject();
myObj.doSomething();

// bytecode 2
   0:   new #2; //class SomeObject
   3:   dup
   4:   invokespecial   #3; //Method SomeObject."<init>":()V
   7:   astore_1
   8:   aload_1
   9:   invokevirtual   #4; //Method SomeObject.doSomething:()V
   12:  return

Those instructions seem very redundant and easy to optimize-out. I’d bet the JIT compiler would handle them if needed.