Java 浅拷贝，深拷贝

     从Java 强引用，软引用，弱引用http://blog.csdn.net/jltxgcy/article/details/35558465一文中，我们看到把一个对象赋值给另一个对象，本质上是增加了引用计数，但是它们都指向同样的堆内存，它们是一个对象。如果我们想要一个独立的对象，改怎么办呢？答案是clone。

1、浅拷贝

     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。

      ShallowCopy.java

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 Student0 implements 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.p改变了s1.p的内容。而s2.name和s2.age没有改变s1.name和s1.age的内容。

2、深拷贝

     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。

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);//耗时
    }
}

     s2.p不能改变s1.p的内容。因为是不同对象。

3、当然我们还有一种深拷贝方法，就是将对象串行化：

     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。

     DeepCopy2.java

import java.io.*;
//Serialization is time-consuming
class 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 Student2 implements 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);//耗时
    }
 
}

      结果：

     s2.p不能改变s1.p的内容。因为是不同对象。

     从图中也能看出将对象进行串行化后进行传递，耗时较多。

Java 浅拷贝，深拷贝,布布扣,bubuko.com

Java 浅拷贝，深拷贝

原文：http://blog.csdn.net/jltxgcy/article/details/35566521