@senninha 嗯， 因为 IDEA 是有提示不要 loop 中+=。 所以我有点怀疑。


所以也自己试验了一遍，100w 次 +=耗时 4 秒多 stringBuilder.append 耗时 1 秒
public class TestString {

public static void main(String[] args) {
testStringBuilder();
}

private static final int loop = 1000000;

public static void testPlus() {
System.out.println(">>> testPlus() <<<");

long start = System.currentTimeMillis();

for (int i = 0; i < loop; i++) {
String str = "";
for (int j = 0; j < 100; j++) {
str += j;
}
}
long end = System.currentTimeMillis();
long cost = end - start;

System.out.println("{str+=} cost=" + cost);
}

public static void testStringBuilder() {
long start = System.currentTimeMillis();

for (int i = 0; i < loop; i++) {
StringBuilder str = new StringBuilder();

for (int j = 0; j < 100; j++) {
str.append(j);
}
}

long end = System.currentTimeMillis();
long cost = end - start;

System.out.println("{stringBuilder.append} cost=" + cost);
}
}