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作者	Object类中最基本又最深层的问题
swofmengtian 发贴: 2 积分: 0	于 2005-11-10 16:23 package mypack; public class MyObject { public static void main(String[] args) { Object me=new Object(); me.clone(); MyObject my=new MyObject(); my.clone(); } }

作者	Re:Object类中最基本又最深层的问题 [Re:swofmengtian]
swofmengtian 发贴: 2 积分: 0	于 2005-11-10 16:26 两个clone()方法都用不了，根本就编译不过，为什么？

作者	Re:Object类中最基本又最深层的问题 [Re:swofmengtian]
wangjiong 发贴: 17 积分: 17	于 2005-11-10 17:23 看你的编译错误信息不就知道了。object 的clone方法是protected，当然不能直接调用。第二个你没有捕捉抛出的异常。

作者

Re:Object类中最基本又最畈愕奈侍?></td></tr><tr class= [Re:swofmengtian]

ranchgirl

版主

发贴: 801
积分: 132

于 2005-11-11 14:46

Q. How to use clone()method, why my code throws CloneNotSupportedException?
A: Make your class implements Cloneable interface, and override the Object.clone() method.
If you don't override the Object.clone() method, the code will be compilable, but throws CloneNotSupportedException. Why, see the following code copied from JDK Object.java.


protected native Object clone() throws CloneNotSupportedException;

作者	Re:Object类中最基本又最深层的问题 [Re:swofmengtian]
ranchgirl 版主发贴: 801 积分: 132	于 2005-11-11 15:03 Read javadoc here: http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#clone()

作者

Re:Object类中最基本又最深层的问题 [Re:swofmengtian]

wallacer

HUST

发贴: 30
积分: 1

于 2005-11-11 20:43

Advice:
To lean java clone method you must carefully understand shadow clone and deep clone. Here are the examples:

shadow clone:


class UnCloneA {
    private int i;
    public UnCloneA(int ii) { i = ii; }
    public void doubleValue() { i *= 2; }
    public String toString() {
        return Integer.toString(i);
    }
}
class CloneB implements Cloneable{
    public int aInt;
    public UnCloneA unCA = new UnCloneA(111);
    public Object clone(){
        CloneB o = null;
        try{
            o = (CloneB)super.clone();
        }catch(CloneNotSupportedException e){
            e.printStackTrace();
        }
        return o;
    }
}
public class CloneMain {
    public static void main(String[] a){
        CloneB b1 = new CloneB();
        b1.aInt = 11;
        System.out.println("before clone,b1.aInt = "+ b1.aInt);
        System.out.println("before clone,b1.unCA = "+ b1.unCA);
                
        CloneB b2 = (CloneB)b1.clone();
        b2.aInt = 22;
        b2.unCA.doubleValue();
        System.out.println("=========================");
        System.out.println("after clone,b1.aInt = "+ b1.aInt);
        System.out.println("after clone,b1.unCA = "+ b1.unCA);
        System.out.println("=========================");
        System.out.println("after clone,b2.aInt = "+ b2.aInt);
        System.out.println("after clone,b2.unCA = "+ b2.unCA);
    }
}

RESULT:
before clone,b1.aInt = 11
before clone,b1.unCA = 111
=================================
after clone,b1.aInt = 11
after clone,b1.unCA = 222
=================================
after clone,b2.aInt = 22
after clone,b2.unCA = 222

deep clone:


class UnCloneA implements Cloneable{
    private int i;
    public UnCloneA(int ii) { i = ii; }
    public void doubleValue() { i *= 2; }
    public String toString() {
        return Integer.toString(i);
    }
    public Object clone(){
        UnCloneA o = null;
        try{
            o = (UnCloneA)super.clone();
        }catch(CloneNotSupportedException e){
            e.printStackTrace();
        }
        return o;
    }
}
class CloneB implements Cloneable{
    public int aInt;
    public UnCloneA unCA = new UnCloneA(111);
    public Object clone(){
        CloneB o = null;
        try{
            o = (CloneB)super.clone();
        }catch(CloneNotSupportedException e){
            e.printStackTrace();
        }
        o.unCA = (UnCloneA)unCA.clone();
        return o;
    }
}
public class CloneMain {
    public static void main(String[] a){
        CloneB b1 = new CloneB();
        b1.aInt = 11;
        System.out.println("before clone,b1.aInt = "+ b1.aInt);
        System.out.println("before clone,b1.unCA = "+ b1.unCA);
                
        CloneB b2 = (CloneB)b1.clone();
        b2.aInt = 22;
        b2.unCA.doubleValue();
        System.out.println("===========================");
        System.out.println("after clone,b1.aInt = "+ b1.aInt);
        System.out.println("after clone,b1.unCA = "+ b1.unCA);
        System.out.println("===========================");
        System.out.println("after clone,b2.aInt = "+ b2.aInt);
        System.out.println("after clone,b2.unCA = "+ b2.unCA);
    }
}

RUN RESULT:
before clone,b1.aInt = 11
before clone,b1.unCA = 111
=================================
after clone,b1.aInt = 11
after clone,b1.unCA = 111
=================================
after clone,b2.aInt = 22
after clone,b2.unCA = 222

There are the principles you must follow:
1. All basic types in java such as int, float, double, and so on of your class field can be cloned automatically.
2. All object types of your class field must be implemented the interface Cloneable, otherwise all the object types in your class field have been cloned point to the original class of its respective class field.

wallacer edited on 2005-11-11 21:03

"your future depends on your dream, so go to sleep."

作者

Re:Object类中最基本又最深层的问题 [Re:swofmengtian]

ftang

版主

发贴: 214
积分: 38

于 2005-11-18 05:18

Oh Boy! Clone() again...agree with wallacer: You MUST understand what is "Shadow Clone" and "Deep Clone" ----which unfortunately you can blame this on SUN, the Clone( ) design is a failure!!!!
The typical example is HashMap.clone(), which is shadow clone...so if the original hashMap value changed, then the copy hashMap value get changed( you still call this is a clone()?)

ps: Object类中最基本又最深层的问题? yeah...maybe to you it is 最深层....

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