Java: Is the method Integer.toString() better than adding empty string to integer type value? [duplicate]

This question already has answers here: Closed 12 years ago.

Possible Duplicate:

Is conversion to String using (“” + <int value>) bad practice?

I am testing some Java codes with PMD rules. One of the rules for efficiency is a 'AddingEmptyString'. Below is a description for the rule.

Finds empty string literals which are being added. This is an inefficient way to con开发者_开发知识库vert any type to a String.

    String s = "" + 123; // bad 
    String t = Integer.toString(456); // ok 

Could you explain why Integer.toString is better than adding empty string to integer type value?

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It's bad because the first way does more operations than the second. The compiler will translate the first line into the equivalent of

String s = "" + Integer.toString(123);

Which has an extra string concatenation when compared to

String t = Integer.toString(456);

Even if the compiler optimizes away the concatenation with the empty string, the purpose of the line of code is much more clear when Integer.toString is used explicitly.

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in the first example you're instantiating a String object ("") and then another String object to hold the result of Integer to String conversion, 2 objects created in all;

The second you're only creating one string object, which is created when you do the Integer.toString()

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It's also bad because String concatenation is a relatively expensive operation. Using StringBuilder would likely be slightly more efficient than your first fragment. You might note that you will commonly see something like System.out.println(""+i) where i is an int but this concatenation is quite unnecessary, not to say wrong. This is the equivalent of ...println(""+Integer.valueOf(i).toString()) which looks a lot more messy but does the same thing. ...println(i) works just fine.