Dao持久层定义sql语句拼接参数之String和StringBuffer区别

 1 public class Test {  
 2     public static void main(String args[]) {  
 3           
 4         String str = "abc";  
 5         StringBuffer sb = new StringBuffer("abc");  
 6         Runtime runtime = Runtime.getRuntime();  
 7         long start = System.currentTimeMillis();  
 8         long startFreememory = runtime.freeMemory();  
 9         for (int i = 0; i < 10000; i++) {  
10             str += i;  
11             //测试StringBuffer时候把注释打开  
12             //sb.append(i);  
13         }  
14         long endFreememory = runtime.freeMemory();  
15         long end = System.currentTimeMillis();  
16         System.out.println("操作耗时:" + (end - start) + "ms," + "内存消耗:"  
17                 + (startFreememory - endFreememory)/1024 + "KB");  
18     }  
19 } 

测试结果：

使用String做10000次向一字符串后添加字符串

操作耗时:1872ms,内存消耗:1301KB

使用StringBuffer做10000次向一字符串后添加字符串

操作耗时:15ms,内存消耗:162KB

差别显著！

Dao持久层定义sql语句拼接参数之String和StringBuffer区别

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