Java设计模式之原型模式

2021-04-25 本文已影响0人 mundane

需求

有一只羊叫tom, 年龄1岁, 颜色是白色, 请编写程序创建和tom属性完全相同的10只羊

传统方式解决克隆羊

直接上代码吧

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;
    }

    @Override
    public String toString() {
        return "Sheep{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", color='" + color + '\'' +
                '}';
    }
}

public class Client {
    public static void main(String[] args) {
        Sheep sheep = new Sheep("tom", 1, "白色");
        Sheep sheep2 = new Sheep(sheep.getName(), sheep.getAge(), sheep.getColor());
        Sheep sheep3 = new Sheep(sheep.getName(), sheep.getAge(), sheep.getColor());
        Sheep sheep4 = new Sheep(sheep.getName(), sheep.getAge(), sheep.getColor());
        Sheep sheep5 = new Sheep(sheep.getName(), sheep.getAge(), sheep.getColor());

        System.out.println(sheep);
        System.out.println(sheep2);
        System.out.println(sheep3);
        System.out.println(sheep4);
        System.out.println(sheep5);
    }
}

输出结果:

Sheep{name='tom', age=1, color='白色'}
Sheep{name='tom', age=1, color='白色'}
Sheep{name='tom', age=1, color='白色'}
Sheep{name='tom', age=1, color='白色'}
Sheep{name='tom', age=1, color='白色'}

分析

优点:
比较好理解, 简单易操作
缺点

在创建新的对象时, 总是需要重新获取原始对象的属性, 如果创建的对象比较复杂, 效率较低
总是需要重新初始化对象, 而不是动态的获得对象运行时的状态, 不够灵活

使用原型模式克隆羊

原型模式介绍

原型模式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, 允许一个对象创建另外一个可定制的对象, 无需知道创建的细节
工作原理: 通过将一个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()

上代码:

public class Sheep implements Cloneable{

    private String name;
    private int age;
    private String color;
    private String address = "蒙古羊";


    public Sheep(String name, int age, String color) {
        this.name = name;
        this.age = age;
        this.color = color;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    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;
    }

    @Override
    public String toString() {
        return "Sheep{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", color='" + color + '\'' +
                ", address='" + address + '\'' +
                '}';
    }

    @Override
    protected Sheep clone() {
        Sheep sheep = null;
        try {
            sheep = (Sheep) super.clone();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return sheep;
    }
}

public class Client {
    public static void main(String[] args) {

        System.out.println("原型模式完成对象的创建");
        Sheep sheep = new Sheep("tom", 1, "白色");
        Sheep sheep2 = sheep.clone();
        Sheep sheep3 = sheep.clone();
        Sheep sheep4 = sheep.clone();
        Sheep sheep5 = sheep.clone();

        System.out.println("sheep2 = " + sheep2);
        System.out.println("sheep3 = " + sheep3);
        System.out.println("sheep4 = " + sheep4);
        System.out.println("sheep5 = " + sheep5);

    }
}

浅拷贝与深拷贝

浅拷贝的介绍

对于数据类型是基本类型的成员变量, 浅拷贝会直接进行值传递, 将属性值复制一份给新的对象
对于数据类型是引用类型的成员变量, 浅拷贝会进行引用传递, 只是将该成员变量的引用值复制一份给新的对象, 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
前面的克隆羊就是浅拷贝
假如Sheep增加一个类型为Sheep的成员变量friendprivate Sheep friend, 这个成员变量在拷贝的时候就只会进行引用传递

深拷贝的介绍

复制对象的所有基本数据类型的成员变量
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, 要对整个对象进行拷贝
深拷贝实现方式1: 重写clone方法实现深拷贝
深拷贝实现方式2: 通过对象序列化实现深拷贝(推荐使用)

上代码:

方式一

首先, 这个DeepCloneableTarget是要拷贝的为引用数据类型的成员变量

public class DeepCloneableTarget implements Serializable, Cloneable {
    private static final long serialVersionUID = 1L;

    private String cloneName;

    private String cloneClass;


    public DeepCloneableTarget(String cloneName, String cloneClass) {
        this.cloneName = cloneName;
        this.cloneClass = cloneClass;
    }

    @Override
    protected DeepCloneableTarget clone() throws CloneNotSupportedException {
        return (DeepCloneableTarget) super.clone();
    }
}

这个DeepProtoType是要拷贝的对象

public class DeepProtoType implements Serializable, Cloneable {

    private String name;
    private DeepCloneableTarget deepCloneableTarget;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public DeepCloneableTarget getDeepCloneableTarget() {
        return deepCloneableTarget;
    }

    public void setDeepCloneableTarget(DeepCloneableTarget deepCloneableTarget) {
        this.deepCloneableTarget = deepCloneableTarget;
    }

    public DeepProtoType() {
    }

    public DeepProtoType(String name, DeepCloneableTarget deepCloneableTarget) {
        this.name = name;
        this.deepCloneableTarget = deepCloneableTarget;
    }

    // 深拷贝, 方式一: 使用clone方法
    @Override
    protected DeepProtoType clone() throws CloneNotSupportedException {
        DeepProtoType deepProtoType = null;
        deepProtoType = (DeepProtoType) super.clone();
        deepProtoType.setDeepCloneableTarget(deepProtoType.getDeepCloneableTarget().clone());
        return deepProtoType;
    }

}

public class Client {
    public static void main(String[] args) throws CloneNotSupportedException {


        DeepProtoType p = new DeepProtoType();
        p.setName("宋江");
        p.setDeepCloneableTarget(new DeepCloneableTarget("大牛", "小牛"));

        // 方式一完成深拷贝
        DeepProtoType p2 = p.clone();
        DeepProtoType p3 = p.clone();
        DeepProtoType p4 = p.clone();
        DeepProtoType p5 = p.clone();

        System.out.println("p.name = " + p.getName() + ", p.getDeepCloneableTarget().hashCode() = "+p.getDeepCloneableTarget().hashCode());
        System.out.println("p2.name = " + p2.getName() + ", p2.getDeepCloneableTarget().hashCode() = "+p2.getDeepCloneableTarget().hashCode());
        System.out.println("p3.name = " + p3.getName() + ", p3.getDeepCloneableTarget().hashCode() = "+p3.getDeepCloneableTarget().hashCode());
        System.out.println("p4.name = " + p4.getName() + ", p4.getDeepCloneableTarget().hashCode() = "+p4.getDeepCloneableTarget().hashCode());
        System.out.println("p5.name = " + p5.getName() + ", p5.getDeepCloneableTarget().hashCode() = "+p5.getDeepCloneableTarget().hashCode());

    }
}

输出结果:

p.name = 宋江, p.getDeepCloneableTarget().hashCode() = 1625635731
p2.name = 宋江, p2.getDeepCloneableTarget().hashCode() = 1580066828
p3.name = 宋江, p3.getDeepCloneableTarget().hashCode() = 491044090
p4.name = 宋江, p4.getDeepCloneableTarget().hashCode() = 644117698
p5.name = 宋江, p5.getDeepCloneableTarget().hashCode() = 1872034366

方式二

public class DeepProtoType implements Serializable, Cloneable {

    private String name;
    private DeepCloneableTarget deepCloneableTarget;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public DeepCloneableTarget getDeepCloneableTarget() {
        return deepCloneableTarget;
    }

    public void setDeepCloneableTarget(DeepCloneableTarget deepCloneableTarget) {
        this.deepCloneableTarget = deepCloneableTarget;
    }

    public DeepProtoType() {
    }

    public DeepProtoType(String name, DeepCloneableTarget deepCloneableTarget) {
        this.name = name;
        this.deepCloneableTarget = deepCloneableTarget;
    }

    // 深拷贝, 方式二: 通过对象的序列化(推荐)
    public DeepProtoType deepClone() {
        ByteArrayOutputStream bos = null;
        ObjectOutputStream oos = null;
        ByteArrayInputStream bis = null;
        ObjectInputStream ois = null;

        try {
            // 序列化
            bos = new ByteArrayOutputStream();
            oos = new ObjectOutputStream(bos);
            oos.writeObject(this);

            // 反序列化
            bis = new ByteArrayInputStream(bos.toByteArray());
            ois = new ObjectInputStream(bis);
            DeepProtoType copy = (DeepProtoType) ois.readObject();
            return copy;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        } finally {
            try {
                bos.close();
                oos.close();
                bis.close();
                ois.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }
}

public class Client {
    public static void main(String[] args) throws CloneNotSupportedException {


        DeepProtoType p = new DeepProtoType();
        p.setName("宋江");
        p.setDeepCloneableTarget(new DeepCloneableTarget("大牛", "小牛"));

        // 方式二完成深拷贝
        DeepProtoType p2 = p.deepClone();
        DeepProtoType p3 = p.deepClone();
        DeepProtoType p4 = p.deepClone();
        DeepProtoType p5 = p.deepClone();


        System.out.println("p.name = " + p.getName() + ", p.getDeepCloneableTarget().hashCode() = "+p.getDeepCloneableTarget().hashCode());
        System.out.println("p2.name = " + p2.getName() + ", p2.getDeepCloneableTarget().hashCode() = "+p2.getDeepCloneableTarget().hashCode());
        System.out.println("p3.name = " + p3.getName() + ", p3.getDeepCloneableTarget().hashCode() = "+p3.getDeepCloneableTarget().hashCode());
        System.out.println("p4.name = " + p4.getName() + ", p4.getDeepCloneableTarget().hashCode() = "+p4.getDeepCloneableTarget().hashCode());
        System.out.println("p5.name = " + p5.getName() + ", p5.getDeepCloneableTarget().hashCode() = "+p5.getDeepCloneableTarget().hashCode());

    }
}

输出结果:

p.name = 宋江, p.getDeepCloneableTarget().hashCode() = 723074861
p2.name = 宋江, p2.getDeepCloneableTarget().hashCode() = 2093176254
p3.name = 宋江, p3.getDeepCloneableTarget().hashCode() = 1854731462
p4.name = 宋江, p4.getDeepCloneableTarget().hashCode() = 317574433
p5.name = 宋江, p5.getDeepCloneableTarget().hashCode() = 885284298

总结

创建新的对象比较复杂时, 可以使用原型模式简化对象的创建, 也能提高效率
不用重新初始化对象, 而是动态的获得对象运行时的状态
如果原始对象增加或减少属性, 其克隆对象也会发生相应的变化, 而无需修改代码
实现深克隆的时候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, 对全新的类来说不难, 但是对已有类进行改造时, 需要修改其源代码, 违背了ocp原则, 这点需要注意

小结

代码地址：
https://github.com/mundane799699/DesignPattern/tree/master/Prototype/src/com/mundane/prototype
参考:

尚硅谷Java设计模式（图解+框架源码剖析）

Java设计模式之原型模式

需求

传统方式解决克隆羊

分析

使用原型模式克隆羊

原型模式介绍

浅拷贝与深拷贝

浅拷贝的介绍

深拷贝的介绍

方式一

方式二

总结

小结

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