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

Method 1 is preferred because it's shorter and also, the compiler automatically converts it to method 2. And there's no performance difference between them.

When compiler can't substitute stringBuilder by itself than it switches from + concat. 

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