String valueOf vs concatenation with empty string

Question

I am working in Java code optimization. I\'m unclear about the difference between String.valueOf or the +\"\" sign:

int intVar = 1;         


        

Answer 1

Well, if you look into the JRE source code, Integer.getChars(...) is the most vital method which actually does the conversion from integer to char[], but it's a package-private method.
So the question is how to get this method called with minimum overhead.
Following is an overview of the 3 approaches by tracing the calls to our target method, please look into the JRE source code to understand this better.

1. "" + intVar compiles to :
   new StringBuilder() => StringBuilder.append(int) => Integer.getChars(...)
2. String.valueOf(intVar) => Integer.toString(intVar) => Integer.getChars(...)
3. Integer.toString(intVar) => Integer.getChars(...)

The first method unnecessarily creates one extra object i.e. the StringBuilder.
The second simply delegates to third method.
So you have the answer now.

PS: Various compile time and runtime optimizations come into play here. So actual performance benchmarks may say something else depending on different JVM implementations which we can't predict, so I generally prefer the approach which looks efficient by looking at the source code.