String, StringBuffer 和StringBuilder 执行时间上的比较

  当遇到连续的字符串操作时，String str=str+"i", StringBuffer str=StringBuffer.append(i) 和StringBuilder str=StringBuilder.append(i) 有什么区别呢？

   思考两秒钟。。。

  用程序验证一下吧。

   代码：

      

package com.blueray.java.test;

public class StringOperation {
	public long stringAdd(long times){
		long startTime=System.currentTimeMillis();
		
		String s="";
		
		for(long i=0;i<times;i++){
			s=s+i;
		}
		
		
		long endTime=System.currentTimeMillis();
		
		long timeBuf= endTime-startTime;
		System.out.println(timeBuf+",");
		return timeBuf;
	}
}

执行代码：

    

public class String_StringBuffer_Compare {
	public static long TIMES_FIFTY = 50L;
	public static long TIMES_ONE_HUNDROD = 100L;
	public static long TIMES_TWO_HUNDROD = 200L;
	public static long TIMES_FIVE_HUNDROD = 500L;
	public static long TIMES_ONE_THOUSAND = 1000L;
	public static long TIMES_FIVE_THOUSAND = 5000L;
	public static long TIMES_TEN_THOUSAND = 10000L;
	public static long TIMES_FIFTY_THOUSAND = 50000L;
	public static long TIMES_HUNDROD_THOUSAND = 100000L;
	public static long[] times = { TIMES_FIFTY, TIMES_ONE_HUNDROD,
			TIMES_TWO_HUNDROD, TIMES_FIVE_HUNDROD, TIMES_ONE_THOUSAND,
			TIMES_FIVE_THOUSAND,TIMES_TEN_THOUSAND,TIMES_FIFTY_THOUSAND,TIMES_HUNDROD_THOUSAND};

	/**
	 * @param args
	 */
	public static void main(String[] args) {
//		for (long time : times) {
//			StringOperation strOpt = new StringOperation();
//			strOpt.stringAdd(time);
//		}
//		for (long time : times) {
//			StringBufferOperation strOpt = new StringBufferOperation();
//			strOpt.stringAppend(time);
//		}
		
		for (long time : times) {
			StringBuilderOperation strOpt = new StringBuilderOperation();
			strOpt.stringAppend(time);
		}


	}

执行4次，结果：

  

50 Times	100 Times	200 Times	500 Times	1000 Times	5000 Times	10000 Times	50000 Times	100000 Times
1	0	2	3	9	63	175	5170	24403
0	1	1	4	11	65	178	5232	24077
0	0	5	3	11	82	179	5266	24133
0	0	1	4	10	77	179	5367	24133

StringConcatOperation:

package com.blueray.java.test;

public class StringConcatOperation {
	public long stringConcat(long times){
		long startTime=System.currentTimeMillis();
		
		String s="";
		
		for(long i=0;i<times;i++){
			s=s.concat(String.valueOf(i));
		}
		
		
		long endTime=System.currentTimeMillis();
		
		long timeBuf= endTime-startTime;
		System.out.println(timeBuf+",");
		return timeBuf;
	}
}

执行结果：

50 Times	100 Times	200 Times	500 Times	1000 Times	5000 Times	10000 Times	50000 Times	100000 Times
1	0	1	2	7	47	99	2699	12650
0	0	1	2	6	46	98	2679	12185
0	1	1	2	6	45	93	2666	12511
1	0	1	2	7	54	94	2669	12143

StringBufferOperation:

package com.blueray.java.test;

public class StringBufferOperation {
	public long stringAppend(long times){
		long startTime=System.currentTimeMillis();
		
		StringBuffer s=new StringBuffer();
		
		for(long i=0;i<times;i++){
			s.append(i);
		}
		
		
		long endTime=System.currentTimeMillis();
		
		long timeBuf= endTime-startTime;
		System.out.println(timeBuf+",");
		return timeBuf;
	}
}

 结果：

   

50 Times	100 Times	200 Times	500 Times	1000 Times	5000 Times	10000 Times	50000 Times	100000 Times
0	0	0	1	1	11	12	12	8
0	0	0	1	1	11	23	15	9
0	0	0	0	1	13	24	15	10
0	0	0	0	1	17	12	11	11

StringBuilderOperation:

   

package com.blueray.java.test;

public class StringBuilderOperation {
	
	public long stringAppend(long times){
		long startTime=System.currentTimeMillis();
		
		StringBuilder s=new StringBuilder();
		
		for(long i=0;i<times;i++){
			s.append(i);
		}
		
		
		long endTime=System.currentTimeMillis();
		
		long timeBuf= endTime-startTime;
		System.out.println(timeBuf+",");
		return timeBuf;
	}
}

 结果：

50 Times	100 Times	200 Times	500 Times	1000 Times	5000 Times	10000 Times	50000 Times	100000 Times
0	0	0	0	1	12	18	9	8
0	0	0	1	1	10	19	11	13
0	0	1	0	1	9	13	7	8
0	0	0	0	1	12	27	9	9

   分析： 

      1. 从图上可以看出，StringBuilder 和StringBuffer的执行效率，要比String 要好

      2. StringBuffer 和StringBuilder，在执行次数从5000到10000时，执行时间都有大幅上升，StringBuilder的时间增加曲线会更陡峭，说明StringBuilder 比StringBuffer,在单线程环境下会更好一些。

   结论：

     在执行时间上，String比两个SB的效率要差。  在不考虑多线程环境下，使用StringBuilder效果会更好。

     不足：

         (1). String 的累加是String 对象类型，而StringBuffer 和StringBuilder则添加的是long 型，虽然不太了解StringBuffer.append添加string 和添加long 有什么区别，但是如果改成append(String),可能比较会更加公平

         (2).没有比较String.concat.