StringBuffer、StringBuilder区别
StringBuffer与 StringBuilder中的方法和功能完全是等价的,只是StringBuffer中的方法大都采用了synchronized关键字进行修饰,因此是线程安全的,支持并发操作,适合多线程中使用。StringBuilder不支持并发操作,线性不安全的,不适合多线程中使用。新引入的StringBuilder类不是线程安全的,但其在单线程中的性能比StringBuffer高。(推荐学习:JAVA视频教程)
接下来,我直接贴上测试过程和结果的代码,一目了然:
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); } }
看一下执行结果:
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
从上面的结果可以看出,不考虑多线程,采用String对象时(我把Count/100),执行时间比其他两个都要高,而采用StringBuffer对象和采用StringBuilder对象的差别也比较明显。由此可见,如果我们的程序是在单线程下运行,或者是不必考虑到线程同步问题,我们应该优先使用StringBuilder类;如果要保证线程安全,自然是StringBuffer。
从后面List的测试结果可以看出,除了对多线程的支持不一样外,这两个类的使用方式和结果几乎没有任何差别。
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