Is there a "fastest way" to construct Strings in Java?

Question

I normally create a String in Java the following way:

String foo = "123456";

However, My lecturer has insisted to me that forming a String using the format method, as so:

String foo = String.format("%s", 123456);

Is much faster.

Also, he says that using the StringBuilder class is even faster.

StringBuilder sb = new StringBuilder();
String foo = sb.append(String.format("%s", 123456)).toString();

Which is the fastest method to create a String, if there even is one?

They could not be 100% accurate as I might not remember them fully.

Answer 1

If there is only one string then:

String foo = "123456";

Is fastest. You'll notice that the String.format line has "%s%" declared in it, so I don't see how the lecturer could possibly think that was faster. Plus you've got a method call on top of it.

However, if you're building a string over time, such as in a for-loop, then you'll want to use a StringBuilder. If you were to just use += then you're building a brand new string every time the += line is called. StringBuilder is much faster since it holds a buffer and appends to that every time you call append.