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
}
}
结果：
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
}
}
结果：
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。