昨天的笔试题， StringBuffer

代码：

     public static void switchStr(StringBuffer x, StringBuffer y) {
         x.append(y);
         System.out.println("(1)" + x);
         y = x;
         System.out.println("(2)" + y);
     }

     public static void main(String args[]) {
         StringBuffer a = new StringBuffer("A");
         StringBuffer b = new StringBuffer("B");
         switchStr(a, b);
         System.out.println("(3)" + a + "," + b);
     }

执行结果

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

 

 

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修改一下

     public static void switchStr(StringBuffer x, StringBuffer y) {
         x = y;
         System.out.println("(1) x = " + x);
         y = x;
         System.out.println("(2) y = " + y);
     }

     public static void main(String args[]) {
         StringBuffer a = new StringBuffer("A");
         StringBuffer b = new StringBuffer("B");
         switchStr(a, b);
         System.out.println("(3) a = " + a);
         System.out.println("(4) b = " + b);
     }

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：

     public static void switchStr(StringBuffer x, StringBuffer y) {
         StringBuffer temp = x;
         x = y;
         System.out.println("(1) x = " + x);
         y = temp;
         System.out.println("(2) y = " + y);
     }

     public static void main(String args[]) {
         StringBuffer a = new StringBuffer("A");
         StringBuffer b = new StringBuffer("B");
         switchStr(a, b);
         System.out.println("(3) a = " + a);
         System.out.println("(4) b = " + b);
     }

结果：

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