Java字符串连接操作的性能问题

 1 package com.test;
 2 
 3 class StringTest {
 4 
 5     public static void main(String[] args) {
 6         
 7         long start = 0;
 8         long count = 100000;
 9         String str = "test String contact..";
10         String result = "";
11         long s1 = System.currentTimeMillis();
12         while (start < count) {
13             result+=str;
14             start++;
15         }
16         long e1 = System.currentTimeMillis();
17         System.out.println("+ 连接执行时间：");
18         System.out.println(e1 - s1);
19         
20         start = 0;
21         str = "test String contact..";
22         result="";
23         long s2 = System.currentTimeMillis();
24         while (start < count) {
25             result=result.concat(str);
26             start++;
27         }
28         long e2 = System.currentTimeMillis();
29         
30         System.out.println("contact 连接执行时间：");
31         System.out.println(e2 - s2);
32         
33         start = 0;
34         str = "test String contact..";
35         result="";
36         StringBuilder sb = new StringBuilder();
37         long s3 = System.currentTimeMillis();
38         while (start < count) {
39             sb.append(str);
40             start++;
41         }
42         long e3 = System.currentTimeMillis();
43         
44         System.out.println("stringbuild 连接执行时间：");
45         System.out.println(e3 - s3);
46         
47         start = 0;
48         str = "test String contact..";
49         result="";
50         StringBuffer sbu = new StringBuffer();
51         long s4 = System.currentTimeMillis();
52         while (start < count) {
53             sbu.append(str);
54             start++;
55         }
56         long e4 = System.currentTimeMillis();
57         
58         System.out.println("stringbuffer 连接执行时间：");
59         System.out.println(e4 - s4);
60         
61         
62     }
63 }

+ 连接执行时间：
156960
contact 连接执行时间：
40896
stringbuild 连接执行时间：
8
stringbuffer 连接执行时间：
7

 1  public String concat(String str) {
 2         int otherLen = str.length();
 3         if (otherLen == 0) {
 4             return this;
 5         }
 6         int len = value.length;
 7         char buf[] = Arrays.copyOf(value, len + otherLen);
 8         str.getChars(buf, len);
 9         return new String(buf, true);
10     }