Question

For example, you want to reverse a string, will there two ways:

first:

String a = "StackOverFlow";
a = new StringBuffer(a).reverse().toString();

and second is:

String a = "StackOverFlow";
StringBuffer b = new StringBuffer(a);
a = b.reverse().toString();

at above code, I have two question:

1) in first code, does java create a “dummy object” StringBuffer in memory before do reverse and change to String.

2) at above code, does first will more optimize than second because It makes GC works more effectively ? (this is a main question I want to ask)

Answer 1

1. The first way will create a very real, not at all a “dummy object” for the StringBuffer.
2. Unless there are other references to b below the last line of your code, the optimizer has enough information to let the environment garbage-collect b as soon as it’s done with toString

The fact that there is no variable for b does not make the object created by new less real. The compiler will probably optimize both snippets into identical bytecode, too.