效能對比結果：StringBuilder>StringBuffer>StringUtils.join>concat>+

效能【指標：時間】對比程式碼：

public class Test {
  List<String> list = new ArrayList<>();
  @Before
  public void init(){
    IntStream.range(0, 100000).forEach((index) -> {
      list.add("str" + index);
    });
  }
  @org.junit.Test
  
 
public void test1() {
    String ss = "";
    long startTime = System.currentTimeMillis();
    for (String s : list) {
      ss += s;
    }
    System.out.println(System.currentTimeMillis() - startTime);
  }
  @org.junit.Test
  public void test2() {
    String ss = "";
    long startTime = System.currentTimeMillis();
    
 
for (String s : list) {
      ss=ss.concat(s);
    }
    System.out.println(System.currentTimeMillis() - startTime);
  }
  @org.junit.Test
  public void test3() {
    StringBuilder ss = new StringBuilder();
    long startTime = System.currentTimeMillis();
    for (String s : list) {
      ss.append(s);
    }
    System.out.println(System.currentTimeMillis() 
 
- startTime);
  }
  @org.junit.Test
  public void test4() {
    long startTime = System.currentTimeMillis();
    StringUtils.join(list);
    System.out.println(System.currentTimeMillis() - startTime);
  }
  @org.junit.Test
  public void test5() {
    StringBuffer ss = new StringBuffer();
    long startTime = System.currentTimeMillis();
    for (String s : list) {
      ss.append(s);
    }
    System.out.println(System.currentTimeMillis() - startTime);
  }
}

耗時結果：

第一種：33809

第二種：8851

第三種：6

第四種：12

第五種：7