Java中StringBuffer和StringBuilder_动力节点Java学院整理

 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); 
   } 
 }