codeql/java/ql/src/Performance/ConcatenationInLoops.java at main · github/codeql · GitHub

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public class ConcatenationInLoops {

public static void main(String[] args) {

Random r = new Random(123);

long start = System.currentTimeMillis();

String s = "";

for (int i = 0; i < 65536; i++)

s += r.nextInt(2);

System.out.println(System.currentTimeMillis() - start); // This prints roughly 4500.

r = new Random(123);

start = System.currentTimeMillis();

StringBuilder sb = new StringBuilder();

for (int i = 0; i < 65536; i++)

sb.append(r.nextInt(2));

s = sb.toString();

System.out.println(System.currentTimeMillis() - start); // This prints 5.

}