将三种方法循环1000万次，代码：

1.public class sbbm {

2.

3.    static String a;

4.    static long time ;

5.    public static void main( String[] args ) throws Exception {

6.       

7.         StringBuilder sb = new StringBuilder();

8.         StringBuilder sb3 = new StringBuilder();

9.        

10.         time = System.currentTimeMillis();

11.          for( int i = 0; i < 10000000; i++ ) {

12.              StringBuilder sb2 = new StringBuilder();

13.              sb2.append( "someStr6ing" );

14.              sb2.append( "someS5tring2" );

15.              sb2.append( "some3Strin4g" );

16.              sb2.append( "so3meStr5ing" );

17.              sb2.append( "so2meSt7ring" );

18.              a = sb2.toString();

19.          }

20.          System.out.println( "Way2="+(System.currentTimeMillis()-time) );

21.          

22.

23.        time = System.currentTimeMillis();

24.        for( int i = 0; i < 10000000; i++ ) {

25.            sb.delete( 0, sb.length() );

26.            sb.append( "someString" );

27.            sb.append( "someString2" );

28.            sb.append( "someStrin4g" );

29.            sb.append( "someStr5ing" );

30.            sb.append( "someSt7ring" );

31.            a = sb.toString();

32.        }

33.        System.out.println( "Way1="+(System.currentTimeMillis()-time) );

34.

35.        time = System.currentTimeMillis();

36.        for( int i = 0; i < 10000000; i++ ) {

37.

38.            sb3.setLength( 0 );

39.            sb3.append( "someStr55ing" );

40.            sb3.append( "some44String2" );

41.            sb3.append( "som55eStrin4g" );

42.            sb3.append( "some66Str5ing" );

43.            sb3.append( "so33meSt7ring" );

44.            a= sb3.toString() ;

45.        }

46.        System.out.println( "Way3="+(System.currentTimeMillis()-time) );

47. 

48.     

49.    }

50.}

注意append的字符串要都不同样，否则会由于java 的String  pool对结果造成影响（即3好于2）

结果：

1.Way2=9438

2.Way1=6281

3.Way3=6469

能够将各方法多反复几次，点到顺序，等
整体来看：方法2好于方法3好于方法1