Java string concatenation efficiency [duplicate]

Question

Is this bad ?

(imagine it's bigger)

int count; //done something to count String myString = "this " + "is " + "my " + "string" + "and " + this.methodCall() + " answer " + "is : " + count; 

or is it better in a StringBuilder/StringBuffer?

Answer 1

Java compiler will convert it into StringBuilder to increase the performance of repeated string concatenation. http://java.sun.com/docs/books/jls/third%5Fedition/html/expressions.html#15.18.1.2

Its when you are concatenating in a loop compiler can't substitute StringBuilder by itself that's when you should consider from concatenation to StringBuilder.

Answer 2

The Javadoc for StringBuffer states from Java 5.0

The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization.

The compiler will combine the string literals so its the same as writing

String myString = "this is my stringand " + this.methodCall() + " answer is : " + count; 

which is the same as

String myString = new StringBuilder().append("this is my stringand ").append(methodCall()).append(" answer is : ").append(count).toString(); 

I wouldn't worry about the performance unless you need to eliminate garbage from your system, in which case you wouldn't use Strings here. (Its highly unlikely you need to worry about it)