Love Java,Love China!

2008年5月25日

when upcasting .....

// codes start
2

class base{//a base class
3

// constructor
5

public base(){
6

System.out.println("base class construct");
7

}
8

// perform
9

public void perform(){
10

System.out.println("base class perform");
11

}
12

// destructor
13

public void finalize(){
14

System.out.println("base class destruct");
15

}
16

}
17

class subbase extends base{// derive from base
20

// constructor
22

public subbase(){
23

System.out.println("sub class construct");
24

}
25

// perform
26

public void perform(){
27

System.out.println("sub class perform");
28

}
29

// destructor
30

public void finalize(){
31

System.out.println("sub class destruct");
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}
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}
34

public class casting{// test casting class
36

// constructor
37

public casting(){
38

System.out.println("begin casting test");
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}
40

public static void main(String args[]){
42

base father = new base();
43

subbase son = new subbase();
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father.perform();
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son.perform();
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father = (base)son; // <1>
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father.perform();
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son = (subbase)father; // <2>
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son.perform();
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father = (base)((subbase)father); // <3>
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father.perform();
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}
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}
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// codes end
60

Today ,when i go for a interview ,the project manager asked me this question !
Acturally ,It's just relate to the knowledge of reference && object !
Be carefull ,Nothing !

posted @ 2008-05-25 19:40 devliu 阅读(116) | 评论 (0) | 编辑收藏

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