java stringbuilder清空的方法

java stringbuilder清空的三种方法

1、新生成一个,旧的由系统自动回收
2、delete 方法
builder1.delete(0, builder.length());
3、Length
StringBuilder val = new StringBuilder();
val.Append(“….”);
val.Length = 0;//清空

        StringBuilder builder = new StringBuilder();  
        long time = System.currentTimeMillis();  
        for(int i=0;i<10000000;i++){  
            builder = new StringBuilder();  
            builder.append("aa");  
            builder.append("bb");  
            builder.append("cc");  
            builder.append("dd");  
            builder.append("ee");  
        }  
        System.out.println("new 耗时:" + (System.currentTimeMillis() - time));  
        long time1 = System.currentTimeMillis(); 
        StringBuilder builder1 = new StringBuilder();
        for(int i=0;i<10000000;i++){  
            builder1.delete(0, builder.length());  
            builder1.append("a");  
            builder1.append("b");  
            builder1.append("c");  
            builder1.append("d");  
            builder1.append("e");  
        }  
        System.out.println("delete 耗时:" + (System.currentTimeMillis() - time1));  
        long time2 = System.currentTimeMillis(); 
        StringBuilder builder2 = new StringBuilder();
        for(int i=0;i<10000000;i++){  
            builder2.setLength(0);  
            builder2.append("1a");  
            builder2.append("1b");  
            builder2.append("1c");  
            builder2.append("1d");  
            builder2.append("1e");  
        }  
        System.out.println("setLenth=0 耗时:" + (System.currentTimeMillis() - time2));  


结果一:

new 耗时:485
delete 耗时:471
setLenth=0 耗时:385

结果二:

new 耗时:621
delete 耗时:411
setLenth=0 耗时:423