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2008年5月25日

when upcasting .....

// codes start
2

class base{//a base class
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// constructor
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public base(){
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System.out.println("base class construct");
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}
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// perform
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public void perform(){
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System.out.println("base class perform");
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}
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// destructor
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public void finalize(){
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System.out.println("base class destruct");
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}
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}
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class subbase extends base{// derive from base
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// constructor
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public subbase(){
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System.out.println("sub class construct");
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}
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// perform
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public void perform(){
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System.out.println("sub class perform");
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}
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// destructor
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public void finalize(){
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System.out.println("sub class destruct");
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}
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}
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public class casting{// test casting class
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// constructor
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public casting(){
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System.out.println("begin casting test");
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}
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public static void main(String args[]){
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base father = new base();
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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
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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 閱讀(109) | 評論 (0) | 編輯收藏

Love Java,Love China!

when upcasting .....

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