昨天的笔试题， StringBuffer

代码：

 1     public static void switchStr(StringBuffer x, StringBuffer y) {
 2         x.append(y);
 3         System.out.println("(1)" + x);
 4         y = x;
 5         System.out.println("(2)" + y);
 6     }
 7 
 8     public static void main(String args[]) {
 9         StringBuffer a = new StringBuffer("A");
10         StringBuffer b = new StringBuffer("B");
11         switchStr(a, b);
12         System.out.println("(3)" + a + "," + b);
13     }

 

执行结果

(1)AB
(2)AB
(3)AB,B

 

 

 
 
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修改一下
 1     public static void switchStr(StringBuffer x, StringBuffer y) {
 2         x = y;
 3         System.out.println("(1) x = " + x);
 4         y = x;
 5         System.out.println("(2) y = " + y);
 6     }
 7 
 8     public static void main(String args[]) {
 9         StringBuffer a = new StringBuffer("A");
10         StringBuffer b = new StringBuffer("B");
11         switchStr(a, b);
12         System.out.println("(3) a = " + a);
13         System.out.println("(4) b = " + b);
14     }

 

执行结果

(1) x = B
(2) y = B
(3) a = A
(4) b = B

a 指向 “A”

b 指向 “B”

x = y ,这时候 x 和 y 同时指向 “B”了

y = x ,这句其实没起作用

 

最终 b x y 同时指向 “B”

a 没变

 

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真的想交换 a b 的话：

 1     public static void switchStr(StringBuffer x, StringBuffer y) {
 2         StringBuffer temp = x;
 3         x = y;
 4         System.out.println("(1) x = " + x);
 5         y = temp;
 6         System.out.println("(2) y = " + y);
 7     }
 8 
 9     public static void main(String args[]) {
10         StringBuffer a = new StringBuffer("A");
11         StringBuffer b = new StringBuffer("B");
12         switchStr(a, b);
13         System.out.println("(3) a = " + a);
14         System.out.println("(4) b = " + b);
15     }

 

结果：

(1) x = B
(2) y = A
(3) a = A
(4) b = B

posted @ 2015-08-12 10:53  马小豆包  阅读(322)  评论(0)  编辑  收藏  举报