Java中的深拷贝(深复制)和浅拷贝(浅复制)

深拷贝(深复制)和浅拷贝(浅复制)是两个比较通用的概念，尤其在C++语言中，若不弄懂，则会在delete的时候出问题，但是我们在这幸好用的是Java。虽然java自动管理对象的回收，但对于深拷贝(深复制)和浅拷贝(浅复制)，我们还是要给予足够的重视，因为有时这两个概念往往会给我们带来不小的困惑。

浅拷贝是指拷贝对象时仅仅拷贝对象本身（包括对象中的基本变量），而不拷贝对象包含的引用指向的对象。深拷贝不仅拷贝对象本身，而且拷贝对象包含的引用指向的所有对象。举例来说更加清楚：对象A1中包含对B1的引用，B1中包含对C1的引用。浅拷贝A1得到A2，A2 中依然包含对B1的引用，B1中依然包含对C1的引用。深拷贝则是对浅拷贝的递归，深拷贝A1得到A2，A2中包含对B2（B1的copy）的引用，B2 中包含对C2（C1的copy）的引用。

若不对clone()方法进行改写，则调用此方法得到的对象即为浅拷贝，下面我们着重谈一下深拷贝。

运行下面的程序，看一看浅拷贝：

 

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class Professor0 implements Cloneable {

    String name;

    intage;

  

    Professor0(String name,int age) {

        this.name = name;

        this.age = age;

    }

  

    publicObject clone() throwsCloneNotSupportedException {

        returnsuper.clone();

    }

}

  

class Student0 implements Cloneable {

    String name;// 常量对象。

    intage;

    Professor0 p;// 学生1和学生2的引用值都是一样的。

  

    Student0(String name,int age, Professor0 p) {

        this.name = name;

        this.age = age;

        this.p = p;

    }

  

    publicObject clone() {

        Student0 o =null;

        try{

            o = (Student0)super.clone();

        }catch (CloneNotSupportedException e) {

            System.out.println(e.toString());

        }

  

        returno;

    }

}

  

public class ShallowCopy {

    publicstatic void main(String[] args) {

        Professor0 p =new Professor0("wangwu",50);

        Student0 s1 =new Student0("zhangsan",18, p);

        Student0 s2 = (Student0) s1.clone();

        s2.p.name ="lisi";

        s2.p.age =30;

        s2.name ="z";

        s2.age =45;

        System.out.println("学生s1的姓名："+ s1.name + "\n学生s1教授的姓名："+ s1.p.name + ","+ "\n学生s1教授的年纪" + s1.p.age);// 学生1的教授

    }

}

s2变了，但s1也变了，证明s1的p和s2的p指向的是同一个对象。这在我们有的实际需求中，却不是这样，因而我们需要深拷贝：

 

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class Professor implements Cloneable {

    String name;

    intage;

  

    Professor(String name,int age) {

        this.name = name;

        this.age = age;

    }

  

    publicObject clone() {

        Object o =null;

        try{

            o =super.clone();

        }catch (CloneNotSupportedException e) {

            System.out.println(e.toString());

        }

        returno;

    }

}

  

class Student implements Cloneable {

    String name;

    intage;

    Professor p;

  

    Student(String name,int age, Professor p) {

        this.name = name;

        this.age = age;

        this.p = p;

    }

  

    publicObject clone() {

        Student o =null;

        try{

            o = (Student)super.clone();

        }catch (CloneNotSupportedException e) {

            System.out.println(e.toString());

        }

        o.p = (Professor) p.clone();

        returno;

    }

}

  

public class DeepCopy {

    publicstatic void main(String args[]) {

        longt1 = System.currentTimeMillis();

        Professor p =new Professor("wangwu",50);

        Student s1 =new Student("zhangsan",18, p);

        Student s2 = (Student) s1.clone();

        s2.p.name ="lisi";

        s2.p.age =30;

        System.out.println("name="+ s1.p.name + ","+ "age=" + s1.p.age);// 学生1的教授不改变。

        longt2 = System.currentTimeMillis();

        System.out.println(t2-t1);

    }

}

当然我们还有一种深拷贝方法，就是将对象串行化：

 

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import java.io.*;

//Serialization is time-consuming

class Professor2 implements Serializable {

    /**

     * 

     */

    privatestatic final long serialVersionUID = 1L;

    String name;

    intage;

  

    Professor2(String name,int age) {

        this.name = name;

        this.age = age;

    }

}

  

class Student2 implements Serializable {

    /**

     * 

     */

    privatestatic final long serialVersionUID = 1L;

    String name;// 常量对象。

    intage;

    Professor2 p;// 学生1和学生2的引用值都是一样的。

  

    Student2(String name,int age, Professor2 p) {

        this.name = name;

        this.age = age;

        this.p = p;

    }

  

    publicObject deepClone() throwsIOException, OptionalDataException,

            ClassNotFoundException {

        // 将对象写到流里

        ByteArrayOutputStream bo =new ByteArrayOutputStream();

        ObjectOutputStream oo =new ObjectOutputStream(bo);

        oo.writeObject(this);

        // 从流里读出来

        ByteArrayInputStream bi =new ByteArrayInputStream(bo.toByteArray());

        ObjectInputStream oi =new ObjectInputStream(bi);

        return(oi.readObject());

    }

  

}

  

public class DeepCopy2 {

  

    /**

     * @param args

     */

    publicstatic void main(String[] args) throws OptionalDataException,

            IOException, ClassNotFoundException {

        longt1 = System.currentTimeMillis();

        Professor2 p =new Professor2("wangwu",50);

        Student2 s1 =new Student2("zhangsan",18, p);

        Student2 s2 = (Student2) s1.deepClone();

        s2.p.name ="lisi";

        s2.p.age =30;

        System.out.println("name="+ s1.p.name + ","+ "age=" + s1.p.age); // 学生1的教授不改变。

        longt2 = System.currentTimeMillis();

        System.out.println(t2-t1);

    }

  

}

但是串行化却很耗时，在一些框架中，我们便可以感受到，它们往往将对象进行串行化后进行传递，耗时较多。