String Concatenation - valueOf or not

Question

So I just perused for a while, all the different questions on here about .valueOf with strings, but they all seem to be about conversions. Comparing .valueOf to just + "".

I want to know if it is worth it or at all necessary to use .valueOf if it is a concatenation.

Example:

LOGGER.info("Final Score: " + String.valueOf(Math.round(finalScore * 100)) + "%");

VS

LOGGER.info("Final Score: " + Math.round(finalScore * 100) + "%");

It seems as though using String.valueOf is unnecessary if you have actual strings to go along with it. I understand it may be better to use .valueOf if you were just converting it and intended to use an empty string.

Answer 1

The source code for String#valueOf(Object) looks like this:

public static String valueOf(Object obj) {
    return (obj == null) ? "null" : obj.toString();
}

So the only difference between valueOf and toString is that valueOf is null-safe. So let's see which one is used if we concatenate a string and an object.

Object foo = null;
System.out.println("foo " + foo); //foo null, no exception thrown
System.out.println("foo " + String.valueOf(foo)); //foo null, no exception thrown

So it looks like there's no difference whatsoever between concatenation and using valueOf in this context.

Answer 2

When we concatenate strings, the compiler actually translates it to StringBuffer.append().

The underlying implementations for StringBuffer.append(int) and String.valueOf(int) both eventually end up calling Integer.getChars(int,int,char[]) except that in case of String.valueOf(), there is a call to Integer.toString(int) first.

To conclude, for the given scenario, directly concatenating would be the way to go. But if you intend to be conscious about memory, then use string-builder to concatenate values first and then log it.