Java中的深拷贝(深复制)和浅拷贝(浅复制)

     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：

 

class Professor0 implements Cloneable {    String name;    int age;     Professor0(String name, int age) {        this.name = name;        this.age = age;    }     public Object clone() throws CloneNotSupportedException {        return super.clone();    }} class Student0implements Cloneable {    String name;// 常量对象。    int age;    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;    }     public Object clone() {        Student0 o = null;        try {            o = (Student0) super.clone();        }catch (CloneNotSupportedException e) {            System.out.println(e.toString());        }         return o;    }} public class ShallowCopy {    public static 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：

 

class Professor implements Cloneable {    String name;    int age;     Professor(String name, int age) {        this.name = name;        this.age = age;    }     public Object clone() {        Object o = null;        try {            o = super.clone();        }catch (CloneNotSupportedException e) {            System.out.println(e.toString());        }        return o;    }} class Student implements Cloneable {    String name;    int age;    Professor p;     Student(String name, int age, Professor p) {        this.name = name;        this.age = age;        this.p = p;    }     public Object clone() {        Student o = null;        try {            o = (Student) super.clone();        }catch (CloneNotSupportedException e) {            System.out.println(e.toString());        }        o.p = (Professor) p.clone();        return o;    }} public class DeepCopy {    public static void main(String args[]) {        long t1 = 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。        long t2 = 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：

 

import java.io.*;//Serialization is time-consumingclass Professor2 implements Serializable {    /**     *     */    private static final long serialVersionUID = 1L;    String name;    int age;     Professor2(String name, int age) {        this.name = name;        this.age = age;    }} class Student2implements Serializable {    /**     *     */    private static final long serialVersionUID = 1L;    String name;// 常量对象。    int age;    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;    }     public Object deepClone() throws IOException, 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     */    public static void main(String[] args) throws OptionalDataException,            IOException, ClassNotFoundException {        long t1 = 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。        long t2 = 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。