stringbuffer和stringbuilder的区别

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public class StringTest {
 
	public static String BASEINFO = "Mr.Y";
	public static final int COUNT = 2000000;
 
	/**
	* 执行一项String赋值测试
	*/
	public static void doStringTest() {
 
		String str = new String(BASEINFO);
		long starttime = System.currentTimeMillis();
		for (int i = 0; i < COUNT / 100; i++) {
			str = str + "miss";
		}
		long endtime = System.currentTimeMillis();
		System.out.println((endtime - starttime)
				+ " millis has costed when used String.");
	}
 
	/**
	* 执行一项StringBuffer赋值测试
	*/
	public static void doStringBufferTest() {
 
		StringBuffer sb = new StringBuffer(BASEINFO);
		long starttime = System.currentTimeMillis();
		for (int i = 0; i < COUNT; i++) {
			sb = sb.append("miss");
		}
		long endtime = System.currentTimeMillis();
		System.out.println((endtime - starttime)
				+ " millis has costed when used StringBuffer.");
	}
 
	/**
	* 执行一项StringBuilder赋值测试
	*/
	public static void doStringBuilderTest() {
 
		StringBuilder sb = new StringBuilder(BASEINFO);
		long starttime = System.currentTimeMillis();
		for (int i = 0; i < COUNT; i++) {
			sb = sb.append("miss");
		}
		long endtime = System.currentTimeMillis();
		System.out.println((endtime - starttime)
				+ " millis has costed when used StringBuilder.");
	}
 
	/**
	* 测试StringBuffer遍历赋值结果
	* 
	* @param mlist
	*/
	public static void doStringBufferListTest(List<String> mlist) {
		StringBuffer sb = new StringBuffer();
		long starttime = System.currentTimeMillis();
		for (String string : mlist) {
			sb.append(string);
		}
		long endtime = System.currentTimeMillis();
		System.out.println(sb.toString() + "buffer cost:"
				+ (endtime - starttime) + " millis");
	}
 
	/**
	* 测试StringBuilder迭代赋值结果
	* 
	* @param mlist
	*/
	public static void doStringBuilderListTest(List<String> mlist) {
		StringBuilder sb = new StringBuilder();
		long starttime = System.currentTimeMillis();
		for (Iterator<String> iterator = mlist.iterator(); iterator.hasNext();) {
			sb.append(iterator.next());
		}
 
		long endtime = System.currentTimeMillis();
		System.out.println(sb.toString() + "builder cost:"
				+ (endtime - starttime) + " millis");
	}
 
	public static void main(String[] args) {
		doStringTest();
		doStringBufferTest();
		doStringBuilderTest();
 
		List<String> list = new ArrayList<String>();
		list.add(" I ");
		list.add(" like ");
		list.add(" BeiJing ");
		list.add(" tian ");
		list.add(" an ");
		list.add(" men ");
		list.add(" . ");
 
		doStringBufferListTest(list);
		doStringBuilderListTest(list);
	}
 
}

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2711 millis has costed when used String.
211 millis has costed when used StringBuffer.
141 millis has costed when used StringBuilder.
 I  like  BeiJing  tian  an  men  . buffer cost:1 millis
 I  like  BeiJing  tian  an  men  . builder cost:0 millis