【设计模式】5.原型模式

原型模式

　　原型模式（Prototype Pattern），使用原型实例复制生成新的对象。若某个类的实例化比较复杂，完全重新创建成本较大，这时可以使用原型模式。这种模式是在内存（堆）中拷贝对象，比直接new一个对象节省资源。对象拷贝的时候构造器是不会执行。

结构图：

Prototype：提供拷贝方法的原型接口

ConcretePrototype：实现拷贝自身方法的类

Java中提供了实现原型模式的方式：

·实现Cloneable接口；

·重写clone方法（默认的protected改为public）

这里Cloneable即可为Prototype。

1. 浅拷贝

　只拷贝对象内的基本数据类型，数组和对象仅拷贝其引用，没有真实拷贝一个新的数组/对象。

例：

public class Pen {
    private String name;
    private float cost;

    public Pen(String name, float cost) {
        this.name = name;
        this.cost = cost;
    }
 }

public class Student implements Cloneable{  // ConcretePrototype
    private String name;
    private int age;
    private Pen pen;

    public Student(String name, int age, Pen pen) {
        this.name = name;
        this.age = age;
        this.pen = pen;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

　　// setter/getter省略
}

public class Test {
    public static void main(String[] args) throws CloneNotSupportedException {
        Student student1 = new Student("jzx",18,new Pen("真彩",3.5f));

        Student student2 = (Student)student1.clone();

        System.out.println("student1的hashCode："+ student1.hashCode());
        System.out.println("student2的hashCode："+ student2.hashCode());
        System.out.println("student1的pen的hashCode："+ student1.getPen().hashCode());
        System.out.println("student2的pen的hashCode："+ student2.getPen().hashCode());
    }
}

输出：

student1的hashCode：1735600054
student2的hashCode：21685669
student1的pen的hashCode：2133927002
student2的pen的hashCode：2133927002

从hashCode可以看出，副本student2中的实例对象pen和student1的实例对象是同一个。

2.深拷贝

　全部拷贝，真正的完全拷贝。

方式一：

　让被拷贝对象中的实例对象的类也实现Cloneable接口，并重写clone方法，同时被拷贝对象的类中重写clone时对实例对象额外拷贝。

例：

public class Pen implements Cloneable{
    private String name;
    private float cost;

    public Pen(String name, float cost) {
        this.name = name;
        this.cost = cost;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

public class Student implements Cloneable{
    private String name;
    private int age;
    private Pen pen;

    public Student(String name, int age,Pen pen) {
        this.name = name;
        this.age = age;
        this.pen = pen;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        Student student = (Student)super.clone();
        student.pen = (Pen)this.pen.clone();
        return student;
    }

　　// setter/getter 省略
}

public class Test {
    public static void main(String[] args) throws CloneNotSupportedException {
        Student student1 = new Student("jzx",18,new Pen("真彩",3.5f));

        Student student2 = (Student)student1.clone();

        System.out.println("student1的hashCode："+ student1.hashCode());
        System.out.println("student2的hashCode："+ student2.hashCode());
        System.out.println("student1的pen的hashCode："+ student1.getPen().hashCode());
        System.out.println("student2的pen的hashCode："+ student2.getPen().hashCode());

    }
}

输出：

student1的hashCode：1735600054
student2的hashCode：21685669
student1的Pen的hashCode：2133927002
student2的Pen的hashCode：1836019240

这时，从hashCode可以看出，副本student2中的实例对象pen和student1的实例对象pen不再是同一个了，是完完全全的拷贝。

方式二：

　被拷贝对象及其中的实例对象都实现序列化，重写clone方法时进行序列化和反序列化。

例：

public class Pen implements Serializable {
    private static final long serialVersionUID = 148964646846L; 
    private String name;
    private float cost;

    public Pen(String name, float cost) {
        this.name = name;
        this.cost = cost;
    }

}

public class Student implements Cloneable,Serializable{
    private static final long serialVersionUID = -146273648822L;
    private String name;
    private int age;
    private Pen pen;

    public Student(String name, int age,Pen pen) {
        this.name = name;
        this.age = age;
        this.pen = pen;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        // 序列化
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = null;
        try {
            oos = new ObjectOutputStream(bos);
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            oos.writeObject(this);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // 反序列化
        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = null;
        try {
            ois = new ObjectInputStream(bis);
        } catch (IOException e) {
            e.printStackTrace();
        }

        Student student = null;
        try {
            student = (Student) ois.readObject();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return student;
    }

　　// setter/getter省略

}

public class Test {
    public static void main(String[] args) throws CloneNotSupportedException {
        Student student1 = new Student("jzx",18,new Pen("真彩",3.5f));

        Student student2 = (Student)student1.clone();

        System.out.println("student1的hashCode："+ student1.hashCode());
        System.out.println("student2的hashCode："+ student2.hashCode());
        System.out.println("student1的pen的hashCode："+ student1.getPen().hashCode());
        System.out.println("student2的pen的hashCode："+ student2.getPen().hashCode());

    }
}

输出：

student1的hashCode：621009875
student2的hashCode：1072408673
student1的pen的hashCode：1554874502
student2的pen的hashCode：1531448569

可见，序列化实现了深拷贝。