测试程序：

package com.gyarmy.string;



import java.util.ArrayList;



import org.junit.Test;



/*

 * StringBuffer 可变的字符序列

 * 

 */

public class TestStringBuffer {

	/*

	 * StringBuilder 5.0以后加入， 线程不安全， 效率高于StringBuffer

	 * 

	 */

	@Test

	public void test2(){

		//效率对比

		//String,StringBuffer, StringBuilder

		String str="";

		long startTime = 0L;

		long endTime = 0L;

		StringBuffer buffer = new StringBuffer("");

		StringBuilder builder = new StringBuilder("");

		

		startTime = System.currentTimeMillis();

		for(int i=0;i<20000;i++)

		{

			buffer.append(String.valueOf(i));

		}

		endTime = System.currentTimeMillis();

		System.out.println("StringBuffer的时间为:"+(endTime-startTime));

		

		startTime = System.currentTimeMillis();

		for(int i=0;i<20000;i++)

		{

			builder.append(String.valueOf(i));

		}

		endTime = System.currentTimeMillis();

		System.out.println("StringBuilder的时间为:"+(endTime-startTime));

		

		startTime = System.currentTimeMillis();

		for(int i=0;i<20000;i++)

		{

			//builder.append(String.valueOf(i));

			str = str+String.valueOf(i);

		}

		endTime = System.currentTimeMillis();

		System.out.println("String的时间为:"+(endTime-startTime));

		

	}

	

	

	@Test

	public void test1(){

		StringBuffer sb = new StringBuffer();

		System.out.println(sb.length());

		sb.append("abcd").append("国家").append("123");

		System.out.println(sb.length());

		System.out.println(sb);

		

		ArrayList list = new ArrayList();

		

		sb.insert(1, "www.youku.com");

		System.out.println(sb);

		sb.reverse();

		System.out.println(sb);

	}

}