Java设计模式——原型模式(实例)
1、克隆羊问题
现有一只羊，姓名：tom，年龄：1，颜色：白色。克隆10只属性完全相同的羊
2、传统方式实例
Sheep
package com.weirdo.prototype;
public class Sheep {
private String name;
private int age;
private String color;
public Sheep(String name, int age, String color) {
this.name = name;
this.age = age;
this.color = color;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
}
Client
package com.weirdo.prototype;
import com.alibaba.fastjson.JSONObject;
public class Client {
public static void main(String[] args) {
//传统的方法
Sheep sheep1 = new Sheep("tom",1,"白色");
Sheep sheep2 = new Sheep(sheep1.getName(),sheep1.getAge(),sheep1.getColor());
Sheep sheep3 = new Sheep(sheep1.getName(),sheep1.getAge(),sheep1.getColor());
Sheep sheep4 = new Sheep(sheep1.getName(),sheep1.getAge(),sheep1.getColor());
Sheep sheep5 = new Sheep(sheep1.getName(),sheep1.getAge(),sheep1.getColor());
//....
System.out.println("sheep1:"+JSONObject.toJSONString(sheep1));
System.out.println("sheep2:"+JSONObject.toJSONString(sheep2));
System.out.println("sheep3:"+JSONObject.toJSONString(sheep3));
System.out.println("sheep4:"+JSONObject.toJSONString(sheep4));
System.out.println("sheep5:"+JSONObject.toJSONString(sheep5));
//...
}
}
3、传统方式优缺点
优点
- 好理解，无脑操作，啪啪啪。
缺点
- 在创建新对象时，总是需要重新获取原始对象的属性，如果创建的对象属性比较多时就贼麻烦。
- 总是重新初始化对象，而不是动态获取对象运行时的状态，不灵活。
改进思路
- Java中Object类是所有类的根类，Object类提供了一个clone()方法，该方法可以将一个Java对象复制一份，但是需要实现clone的Java类必须实现一个接口Cloneable，改接口表示该类能够复制且具有复制的能力，即原型模式。
4、原型模式基本介绍
- 原型模式(Prototype模式)是指：用原型实例指定创建对象的种类，并且通过拷贝这些原型，创建新的对象。
- 原型模式是一种创建型设计模式，允许一个对象再创建另外一个可定制的对象，无需知道如何创建的细节。
- 工作原理是：通过将一个原型对象传给那个要发动创建的对象,这个要发动创建的对象通过请求原型对象拷贝它们自己来实施创建，即对象.clone
5、原型模式解决克隆羊问题实例(浅拷贝)
Sheep
package com.weirdo.prototype.improve;
public class Sheep implements Cloneable{
private String name;
private Integer age;
private String color;
public Sheep(String name, int age, String color) {
this.name = name;
this.age = age;
this.color = color;
}
@Override
protected Object clone() {
Object obj = null;
try {
obj = super.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
return obj;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
}
Client
package com.weirdo.prototype.improve;
import com.alibaba.fastjson.JSONObject;
public class Client {
public static void main(String[] args) {
System.out.println("原型模式完成对象的创建");
Sheep sheep1 = new Sheep("tom", 1, "白色");
//克隆
Sheep sheep2 = (Sheep)sheep1.clone();
Sheep sheep3 = (Sheep)sheep1.clone();
Sheep sheep4 = (Sheep)sheep1.clone();
Sheep sheep5 = (Sheep)sheep1.clone();
System.out.println("sheep1=" + JSONObject.toJSONString(sheep1));
System.out.println("sheep2=" + JSONObject.toJSONString(sheep2));
System.out.println("sheep3=" + JSONObject.toJSONString(sheep3));
System.out.println("sheep4=" + JSONObject.toJSONString(sheep4));
System.out.println("sheep5=" + JSONObject.toJSONString(sheep5));
}
}
6、浅拷贝与深拷贝
6.1 浅拷贝
- 对于数据类型是基本数据类型的成员变量，浅拷贝会直接进行值传递，也就是将该属性值复制一份给新的对象。
- 对于数据类型是引用数据类型的成员变量，比如说成员变量是某个数组、某个类的对象等，那么浅拷贝会进行
引用传递，也就是只是将该成员变量的引用值（内存地址)复制一份给新的对象。因为实际上两个对象的该成员变量都指向同一个实例。在这种情况下，在一个对象中修改该成员变量会影响到另一个对象的该成员变量值。 - 浅拷贝是使用默认的
clone()方法来实现的，即sheep=(Sheep)super.clone(); - 以上克隆羊实例便是使用的浅拷贝
6.2 深拷贝
- 复制对象的所有基本数据类型的成员变量值
- 为所有引用数据类型的成员变量申请存储空间，并复制每个引用数据类型成员变量所引用的对象，直到该对象可达的所有对象。也就是说，对象进行深拷贝要对整个对象(包括对象的引用类型)进行拷贝
- 深拷贝实现方式1：重写clone方法来实现深拷贝
- 深拷贝实现方式2：通过对象序列化实现深拷贝(推荐)
7、浅拷贝实例
以上克隆羊的实例就是浅拷贝，但是不适合论证浅拷贝拷贝的是引用地址。
因为Sheep中的属性，age拷贝的是值，改变其大小不回影响拷贝后属性，name和color都是引用类型，无法改变其内容。
以下将详细论证浅拷贝，对于基本类型来说拷贝的是值，对于其他类型的数据来说拷贝的是引用地址。
Sheep
package com.weirdo.prototype.shallowClone;
public class Sheep implements Cloneable{
private String name;
private int age;
private String color;
private SheepWeight sheepWeight;
public Sheep(String name, int age, String color,SheepWeight sheepWeight) {
this.name = name;
this.age = age;
this.color = color;
this.sheepWeight = sheepWeight;
}
@Override
protected Object clone() {
Object obj = null;
try {
obj = super.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
return obj;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
public SheepWeight getSheepWeight() {
return sheepWeight;
}
public void setSheepWeight(SheepWeight sheepWeight) {
this.sheepWeight = sheepWeight;
}
}
SheepWeight
package com.weirdo.prototype.shallowClone;
public class SheepWeight {
private int sheepWeight;
public SheepWeight (int sheepWeight){
this.sheepWeight = sheepWeight;
}
public int getSheepWeight() {
return sheepWeight;
}
public void setSheepWeight(int sheepWeight) {
this.sheepWeight = sheepWeight;
}
}
Client
package com.weirdo.prototype.shallowClone;
import com.alibaba.fastjson.JSONObject;
public class Client {
public static void main(String[] args) {
System.out.println("浅拷贝实例");
//tom的体重
SheepWeight sheepWeight = new SheepWeight(20);
//new一个羊，并设置它的体重和其它属性
Sheep sheep1 = new Sheep("tom", 1, "白色",sheepWeight);
//开始拷贝
Sheep sheep2 = (Sheep)sheep1.clone();
Sheep sheep3 = (Sheep)sheep1.clone();
Sheep sheep4 = (Sheep)sheep1.clone();
Sheep sheep5 = (Sheep)sheep1.clone();
System.out.println("sheep1=" + JSONObject.toJSONString(sheep1));
System.out.println("sheep2=" + JSONObject.toJSONString(sheep2));
System.out.println("sheep3=" + JSONObject.toJSONString(sheep3));
System.out.println("sheep4=" + JSONObject.toJSONString(sheep4));
System.out.println("sheep5=" + JSONObject.toJSONString(sheep5));
System.out.println("去了一年非洲，tom吃胖了，颜色也变了");
//改变sheepWeight，sheepWeight属性在SheepWeight类中是一个基本类型，但在Sheep类中则是一个引用地址
//此时改变SheepWeight中的sheepWeight属性值，对于Sheep类来说引用地址不变但值变了，因此拷贝之后的属性也将跟着改变
sheepWeight.setSheepWeight(40);
//浅拷贝对于基本类型是直接拷贝的值，因此拷贝之后的属性不会跟着改变
sheep1.setAge(2);
//此处表面上看是改变了原型的color属性值，但实际上是改变了原型color的引用地址(无法改变String类型的内容)
//由于浅拷贝对于String类型是拷贝的引用地址，因此改变原型的color的引用地址，拷贝后的color引用地址不会变，也即拷贝后的color属性仍是指向“白色”的地址
sheep1.setColor("黑色");
//如果用一下方式改变原型的sheepWeight属性值，则拷贝后的数据不会受到影响，因为以下方式是改变了Sheep中对于sheepWeight的引用地址
//sheep1.setSheepWeight(new SheepWeight(45));
System.out.println("sheep1=" + JSONObject.toJSONString(sheep1));
System.out.println("sheep2=" + JSONObject.toJSONString(sheep2));
System.out.println("sheep3=" + JSONObject.toJSONString(sheep3));
System.out.println("sheep4=" + JSONObject.toJSONString(sheep4));
System.out.println("sheep5=" + JSONObject.toJSONString(sheep5));
}
}
运行结果
8、深拷贝实例
8.1 重写clone方法来实现深拷贝
Person
package com.weirdo.prototype.deepClone;
public class Person implements Cloneable {
private String name;
private int age;
private String sex;
private Weight weight;
public Person(String name, int age, String sex, Weight weight) {
this.name = name;
this.age = age;
this.sex = sex;
this.weight = weight;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Weight getWeight() {
return weight;
}
public void setWeight(Weight weight) {
this.weight = weight;
}
/**
* 深拷贝 - 方式1 通过重写clone方法来实现
* @return
*/
@Override
protected Object clone() {
Person person = null;
try {
person = (Person)super.clone();
//对于引用类型单独处理
person.setWeight((Weight) weight.clone());
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
return person;
}
}
Weight
package com.weirdo.prototype.deepClone;
import java.io.Serializable;
public class Weight implements Cloneable, Serializable {
private int weight;
public Weight(int weight){
this.weight = weight;
}
public int getWeight() {
return weight;
}
public void setWeight(int weight) {
this.weight = weight;
}
@Override
protected Object clone() {
Weight weight = null;
try {
weight = (Weight)super.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
return weight;
}
}
Client
package com.weirdo.prototype.deepClone;
import com.alibaba.fastjson.JSONObject;
public class Client {
public static void main(String[] args) throws CloneNotSupportedException {
//方式1：重写clone方法来实现深拷贝
Weight personWeight = new Weight(120);
Person person1 = new Person("小明",18,"男",personWeight);
Person person2 = (Person) person1.clone();
System.out.println("方式1：重写clone方法来实现深拷贝");
System.out.println("person1："+ JSONObject.toJSONString(person1));
System.out.println("person2："+ JSONObject.toJSONString(person2));
System.out.println("小明去了一趟泰国，一年后...");
person1.setAge(19);
person1.setSex("女");
personWeight.setWeight(95);
System.out.println("person1："+ JSONObject.toJSONString(person1));
System.out.println("person2："+ JSONObject.toJSONString(person2)+"------------>深拷贝，拷贝后的数据不受原来属性变更影响");
}
}
运行结果
8.2 通过对象序列化实现深拷贝
Dog
package com.weirdo.prototype.deepClone;
import java.io.*;
public class Dog implements Serializable {
private String name;
private int age;
private String sex;
private Weight weight;
public Dog(String name,int age,String sex,Weight weight){
this.name = name;
this.age = age;
this.sex = sex;
this.weight = weight;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Weight getWeight() {
return weight;
}
public void setWeight(Weight weight) {
this.weight = weight;
}
/**
* 深拷贝 - 方式2 通过对象的序列化实现 (推荐)
* @return
*/
public Dog serializableClone() {
//创建流对象
ByteArrayOutputStream bos = null;
ObjectOutputStream oos = null;
ByteArrayInputStream bis = null;
ObjectInputStream ois = null;
try {
//序列化
bos = new ByteArrayOutputStream();
oos = new ObjectOutputStream(bos);
//当前这个对象以对象流的方式输出
oos.writeObject(this);
//反序列化
bis = new ByteArrayInputStream(bos.toByteArray());
ois = new ObjectInputStream(bis);
Dog copyObj = (Dog)ois.readObject();
return copyObj;
} catch (Exception e) {
e.printStackTrace();
return null;
} finally {
//关闭流
try {
bos.close();
oos.close();
bis.close();
ois.close();
} catch (Exception e2) {
System.out.println(e2.getMessage());
}
}
}
}
Weight
package com.weirdo.prototype.deepClone;
import java.io.Serializable;
public class Weight implements Cloneable, Serializable {
private int weight;
public Weight(int weight){
this.weight = weight;
}
public int getWeight() {
return weight;
}
public void setWeight(int weight) {
this.weight = weight;
}
@Override
protected Object clone() {
Weight weight = null;
try {
weight = (Weight)super.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
return weight;
}
}
Client
package com.weirdo.prototype.deepClone;
import com.alibaba.fastjson.JSONObject;
public class Client {
public static void main(String[] args) throws CloneNotSupportedException {
//方式2：通过序列化来实现深拷贝
Weight dogWeight = new Weight(40);
Dog dog1 = new Dog("大黄",1,"公",dogWeight);
Dog dog2 = dog1.serializableClone();
System.out.println("方式2：通过序列化来实现深拷贝");
System.out.println("dog1："+ JSONObject.toJSONString(dog1));
System.out.println("dog2："+ JSONObject.toJSONString(dog2));
System.out.println("大黄去了一趟泰国，一年后...");
dog1.setAge(2);
dog1.setSex("母");
dogWeight.setWeight(35);
System.out.println("dog1："+ JSONObject.toJSONString(dog1));
System.out.println("dog2："+ JSONObject.toJSONString(dog2)+"------------>深拷贝，拷贝后的数据不受原来属性变更影响");
}
}
运行结果
9、原型模式的注意事项和细节
- 创建新对象比较复杂是，可以利用原型模式
简化对象的创建过程，同时也能提高效率 - 不用重新初始化对象，而是动态地获得对象运行时的状态
- 如果原始对象发生变化，其它克隆对象也会发生相应的变化，无需修改代码
- 在实现深克隆时可能需要比较复杂的代码
缺点：需要为每一个类配备一个克隆方法，这对全新的类来说不是很难。但对已有的类进行改造时，需要修改其源代码，违背了开闭原则(OCP)。