在开发过程中，创建多个数据相同的对象，每次new都开销比较大，在这里可以使用对象克隆，以先创建的原型对象为模板进行对象的复制。这种模式是实现了一个原型接口，该接口用于创建当前对象的克隆。当直接创建对象的代价比较大时，则采用这种模式。例如，一个对象需要在一个高代价的数据库操作之后被创建。我们可以缓存该对象，在下一个请求时返回它的克隆，在需要的时候更新数据库，以此来减少数据库调用

浅克隆

在浅克隆中，如果原型对象的成员变量是值类型，将复制一份给克隆对象；如果原型对象的成员变量是引用类型，则将引用对象的地址复制一份给克隆对象，也就是说原型对象和克隆对象的成员变量指向相同的内存地址

public class Person implements  Cloneable{​int num;String name;​public Person() {}​public Person(int num, String name) {this.num = num;this.name = name;}​public int getNum() {return num;}​public void setNum(int num) {this.num = num;}​public String getName() {return name;}​public void setName(String name) {this.name = name;}​​​@Overrideprotected Person clone() throws CloneNotSupportedException {Person person = (Person)super.clone();return person;}​@Overridepublic String toString() {return "Person{" +"num=" + num +", name='" + name + '\'' +'}';}}

 public class Test {​public static void main(String[] args) throws CloneNotSupportedException {​Person p1 = new Person(100,"jim");Person p2 =p1.clone();//clone方法 返回一个新对象p2.name = "tom";System.out.println(p1);//100 ,jimSystem.out.println(p2);//100 tom​System.out.println(p1==p2);//false​}}

深克隆

多层克隆

在深克隆中，无论原型对象的成员变量是值类型还是引用类型，都将复制一份给克隆对象，深克隆将原型对象的所有引用对象也复制一份给克隆对象。简单来说，在深克隆中，除了对象本身被复制外，对象所包含的所有成员变量也将复制

 public class Person implements  Cloneable{​int num;String name;Address address;​public Person() {​}​public Person(int num, String name) {this.num = num;this.name = name;}​public int getNum() {return num;}​public void setNum(int num) {this.num = num;}​public String getName() {return name;}​public void setName(String name) {this.name = name;}​public Address getAddress() {return address;}​public void setAddress(Address address) {this.address = address;}​@Overrideprotected Person clone() throws CloneNotSupportedException {Person person = (Person)super.clone();person.address = address.clone();   //深度复制  联同person中关联的对象也一同克隆.return person;}​@Overridepublic String toString() {return "Person{" +"num=" + num +", name='" + name + '\'' +", address=" + address +'}';}}​

 public class Address  implements Cloneable{​String  address;​public String getAddress() {return address;}​public void setAddress(String address) {this.address = address;}​@Overridepublic String toString() {return "Address{" +"address='" + address + '\'' +'}';}​@Overrideprotected Address clone() throws CloneNotSupportedException {return (Address) super.clone();}}

序列化

public class Address  implements Serializable {​String  address;​public String getAddress() {return address;}​public void setAddress(String address) {this.address = address;}​@Overridepublic String toString() {return "Address{" +"address='" + address + '\'' +'}';}​}

public class Person implements Serializable {​int num;String name;Address address;​public Person() {}​public Person(int num, String name) {this.num = num;this.name = name;}​public int getNum() {return num;}​public void setNum(int num) {this.num = num;}​public String getName() {return name;}​public void setName(String name) {this.name = name;}​public Address getAddress() {return address;}​public void setAddress(Address address) {this.address = address;}​/*** 自定义克隆方法* @return*/public Person myclone() {Person person = null;try { // 将该对象序列化成流,因为写在流里的是对象的一个拷贝，而原对象仍然存在于JVM里面。所以利用这个特性可以实现对象的深拷贝ByteArrayOutputStream baos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(baos);oos.writeObject(this);// 将流序列化成对象ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());ObjectInputStream ois = new ObjectInputStream(bais);person = (Person) ois.readObject();} catch (IOException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();}return person;}​​@Overridepublic String toString() {return "Person{" +"num=" + num +", name='" + name + '\'' +", address=" + address +'}';}}

 练习

题目页面 (kamacoder.com)

import java.util.Scanner;public class Main {public static void main(String[] args) throws CloneNotSupportedException {Scanner scanner = new Scanner(System.in);int num = scanner.nextInt();while(num-->0){String color = scanner.next();int width = scanner.nextInt();int height = scanner.nextInt();Prototype prototype = new Prototype(color, width, height);Prototype clone = prototype.clone();System.out.println(clone.toString());}}
}class Prototype implements Cloneable{private String color;private int width;private int height;public Prototype(String color, int width, int height) {this.color = color;this.width = width;this.height = height;}@Overridepublic String toString() {return "Color: " + color + ", Width: " + width + ", Height: " + height;}@Overrideprotected Prototype clone() throws CloneNotSupportedException {return (Prototype) super.clone();}}