Clearing a string buffer/builder after loop

Question

How do you clear the string buffer in Java after a loop so the next iteration uses a clear string buffer?

Answer 1

Already good answer there. Just add a benchmark result for StringBuffer and StringBuild performance difference use new instance in loop or use setLength(0) in loop.

The summary is: In a large loop

• StringBuilder is much faster than StringBuffer
• Create new StringBuilder instance in loop have no difference with setLength(0). (setLength(0) have very very very tiny advantage than create new instance.)
• StringBuffer is slower than StringBuilder by create new instance in loop
• setLength(0) of StringBuffer is extremely slower than create new instance in loop.

Very simple benchmark (I just manually changed the code and do different test ):

public class StringBuilderSpeed {
public static final char ch[] = new char[]{'a','b','c','d','e','f','g','h','i'};

public static void main(String a[]){
    int loopTime = 99999999;
    long startTime = System.currentTimeMillis();
    StringBuilder sb = new StringBuilder();
    for(int i = 0 ; i < loopTime; i++){
        for(char c : ch){
            sb.append(c);
        }
        sb.setLength(0);
    }
    long endTime = System.currentTimeMillis();
    System.out.println("Time cost: " + (endTime - startTime));
}

}

New StringBuilder instance in loop: Time cost: 3693, 3862, 3624, 3742

StringBuilder setLength: Time cost: 3465, 3421, 3557, 3408

New StringBuffer instance in loop: Time cost: 8327, 8324, 8284

StringBuffer setLength Time cost: 22878, 23017, 22894

Again StringBuilder setLength to ensure not my labtop got some issue to use such long for StringBuffer setLength :-) Time cost: 3448