Java中StringBuilder的清空方法比较

StringBuilder 没有提供clear或empty方法。
清空有3种方法：
1）使用delete
2）新生成一个，旧的由系统自动回收
3）使用setLength

将三种方法循环1000万次，代码：

public class sbbm {

    static String a;
    static long time ;
    public static void main( String[] args ) throws Exception {
        
         StringBuilder sb = new StringBuilder();
         StringBuilder sb3 = new StringBuilder();
         
        time = System.currentTimeMillis();
        for( int i = 0; i < 10000000; i++ ) {
            sb.delete( 0, sb.length() );
            sb.append( "someString" );
            sb.append( "someString2" );
            sb.append( "someStrin4g" );
            sb.append( "someStr5ing" );
            sb.append( "someSt7ring" );
            a = sb.toString();
        }
        System.out.println( "Way1="+(System.currentTimeMillis()-time) );

         time = System.currentTimeMillis();
          for( int i = 0; i < 10000000; i++ ) {
              StringBuilder sb2 = new StringBuilder();
              sb2.append( "someStr6ing" );
              sb2.append( "someS5tring2" );
              sb2.append( "some3Strin4g" );
              sb2.append( "so3meStr5ing" );
              sb2.append( "so2meSt7ring" );
              a = sb2.toString();
          }
          System.out.println( "Way2="+(System.currentTimeMillis()-time) );
           
        time = System.currentTimeMillis();
        for( int i = 0; i < 10000000; i++ ) {

            sb3.setLength( 0 );
            sb3.append( "someStr55ing" );
            sb3.append( "some44String2" );
            sb3.append( "som55eStrin4g" );
            sb3.append( "some66Str5ing" );
            sb3.append( "so33meSt7ring" );
            a= sb3.toString() ;
        }
        System.out.println( "Way3="+(System.currentTimeMillis()-time) );
  
      
    }
}

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