StringBuilder vs String concatenation in toString() in Java

Question

Given the 2 toString() implementations below, which one is preferred:

public String toString(){     return "{a:"+ a + ", b:" + b + ", c: " + c +"}"; } 

or

public String toString(){     StringBuilder sb = new StringBuilder(100);     return sb.append("{a:").append(a)           .append(", b:").append(b)           .append(", c:").append(c)           .append("}")           .toString(); } 

?

More importantly, given we have only 3 properties it might not make a difference, but at what point would you switch from + concat to StringBuilder?

Answer 1

Version 1 is preferable because it is shorter and the compiler will in fact turn it into version 2 - no performance difference whatsoever.

More importantly given we have only 3 properties it might not make a difference, but at what point do you switch from concat to builder?

At the point where you're concatenating in a loop - that's usually when the compiler can't substitute StringBuilder by itself.