读Java编程艺术之笔记（浅复制/深复制）

浅复制（shallow copy），指在复制源对象中，如果某个成员数据是一个对象（除String和所有基本类型的包装类对象之外），clone()方法只是复制这个成员对象的引用，即，在复制后的对象中，它所具有的成员对象，只是对原来成员对象的引用，并没有真正复制这个成员对象。但对其他成员数据clone()则执行真正的复制，即分配内存，并将它们拷贝到这个内存中。所以浅复制的对象对其成员对象的任何修改，实际上是对源对象中成员对象的修改。
例如：

class SomeClass implements Cloneable{
    OtherClass other;
    Integer myInt;
    int n;
    SomeClass(String title, int n){
        other = new OtherClass(title);
        myInt = new Integer(100);
        this.n = n;
    }
    void setTitle(String title){
        other.setName(title);
    }
    void setN(int n){
        this.n = n;
    }
    void setInteger(int n){
        myInt = n;
    }
    public String toString(){
        return "other:　"+other+" n: "+n+" myInt: "+myInt;
    }
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

class OtherClass{
    String name;
    OtherClass(String name){
        this.name = name;
    }
    void setName(String name){
        this.name = name;
    }
    public String toString(){
        return name;
    }
}

public class CloneableTest {
    public static void main(String[] args) throws CloneNotSupportedException{
        SomeClass sourceObj = new SomeClass("Java", 10);
        SomeClass targetObj = (SomeClass)sourceObj.clone();
        System.out.println("content of sourceObj: "+sourceObj);
        System.out.println("content of targetObj: "+targetObj);
        
        targetObj.setTitle("JSP");
        targetObj.setN(20);
        targetObj.setInteger(20);
        System.out.println("After modified(shallow copy)");
        System.out.println("content of sourceObj: "+sourceObj);
        System.out.println("content of targetObj: "+targetObj);
    }
}

其执行结果：

content of sourceObj: other:　Java n: 10 myInt: 100
content of targetObj: other:　Java n: 10 myInt: 100
After modified(shallow copy)
content of sourceObj: other:　JSP n: 10 myInt: 100
content of targetObj: other:　JSP n: 20 myInt: 20

在运行时刻，Object中的clone()识别出你要复制的是哪一个对象，然后为此对象分配空间，并进行对象的复制，将原始对象的内容一一复制到新对象的存储空间中。继承自java.lang.Object类的clone()方法是浅复制。

那么如何执行深复制呢？提供两种改法：

/* 深复制 1 */
class SomeClass implements Cloneable{
    OtherClass other;
    Integer myInt;
    int n;
    SomeClass(String title, int n){
        other = new OtherClass(title);
        myInt = new Integer(100);
        this.n = n;
    }
    void setTitle(String title){
        other.setName(title);
    }
    void setN(int n){
        this.n = n;
    }
    void setInteger(int n){
        myInt = n;
    }
    public String toString(){
        return "other:　"+other+" n: "+n+" myInt: "+myInt;
    }
    protected Object clone() throws CloneNotSupportedException{
        SomeClass some = (SomeClass)super.clone();
　　　　　//为其成员对象执行真正的复制
        some.other = (OtherClass)other.clone();
        return some;
    }
}

//此时需要成员对象的扩展Cloneable接口
class OtherClass implements Cloneable{
    String name;
    OtherClass(String name){
        this.name = name;
    }
    void setName(String name){
        this.name = name;
    }
    public String toString(){
        return name;
    }
    protected Object clone() throws CloneNotSupportedException{
        return super.clone();    
    }
}

public class CloneableTest {
    public static void main(String[] args) throws CloneNotSupportedException{
        SomeClass sourceObj = new SomeClass("Java", 10);
        SomeClass targetObj = (SomeClass)sourceObj.clone();
        System.out.println("content of sourceObj: "+sourceObj);
        System.out.println("content of targetObj: "+targetObj);
        
        targetObj.setTitle("JSP");
        targetObj.setN(20);
        targetObj.setInteger(20);
        System.out.println("After modified(deep copy)");
        System.out.println("content of sourceObj: "+sourceObj);
        System.out.println("content of targetObj: "+targetObj);
    }
}

/* 深复制 2 */ 
class SomeClass implements Cloneable{
    OtherClass other;
    Integer myInt;
    int n;
    SomeClass(SomeClass someClass){
　　　　　//此处执行所有成员数组的复制         other = new OtherClass(someClass.other.toString());
        myInt = someClass.getInteger();
        n = someClass.getN();    
    }
    SomeClass(String title, int n){
        other = new OtherClass(title);
        myInt = new Integer(100);
        this.n = n;
    }
    void setTitle(String title){
        other.setName(title);
    }
    void setN(int n){
        this.n = n;
    }
    void setInteger(int n){
        myInt = n;
    }
    Integer getInteger(){
        return myInt;    
    }
    int getN(){
        return n;    
    }
    public String toString(){
        return "other:　"+other+" n: "+n+" myInt: "+myInt;
    }
    protected Object clone() throws CloneNotSupportedException{
        SomeClass some = new SomeClass(this);
        return some;
    }
}

class OtherClass {
    String name;
    OtherClass(String name){
        this.name = name;
    }
    void setName(String name){
        this.name = name;
    }
    public String toString(){
        return name;
    }
}

public class CloneableTest {
    public static void main(String[] args) throws CloneNotSupportedException{
        SomeClass sourceObj = new SomeClass("Java", 10);
        SomeClass targetObj = (SomeClass)sourceObj.clone();
        System.out.println("content of sourceObj: "+sourceObj);
        System.out.println("content of targetObj: "+targetObj);
        
        targetObj.setTitle("JSP");
        targetObj.setN(20);
        targetObj.setInteger(20);
        System.out.println("After modified(deep copy)");
        System.out.println("content of sourceObj: "+sourceObj);
        System.out.println("content of targetObj: "+targetObj);
    }
}

上述两段代码的执行结构都是：

content of sourceObj: other:　Java n: 10 myInt: 100
content of targetObj: other:　Java n: 10 myInt: 100
After modified(deep copy)
content of sourceObj: other:　Java n: 10 myInt: 100
content of targetObj: other:　JSP n: 20 myInt: 20