原型模式

1.基础知识：

定义∶

指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

不需要知道任何创建的细节，不调用构造函数

类型∶创建型

适用场景

类初始化消耗较多资源

new产生的一个对象需要非常繁琐的过程（数据准备、访问权限等）

构造函数比较复杂

循环体中生产大量对象时

优点

原型模式性能比直接new一个对象性能高

简化创建过程

缺点

必须配备克隆方法

对克隆复杂对象或对克隆出的对象进行复杂改造时，容易引入风险

深拷贝、浅拷贝要运用得当

2.实战

对象接口实现Cloneable接口重写clone()方法

public class Mail implements Cloneable{
    private String name;
    private String emailAddress;
    private String content;
    public Mail(){
        System.out.println("Mail Class Constructor");
    }

    public String getName() {
        return name;
    }

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

    public String getEmailAddress() {
        return emailAddress;
    }

    public void setEmailAddress(String emailAddress) {
        this.emailAddress = emailAddress;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    @Override
    public String toString() {
        return "Mail{" +
                "name='" + name + '\'' +
                ", emailAddress='" + emailAddress + '\'' +
                ", content='" + content + '\'' +
                '}'+super.toString();
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        System.out.println("clone mail object");
        return super.clone();
    }
}

public class MailUtil {
    public static void sendMail(Mail mail) {
        //这里使用占位符{}
        String outputContent = "向{0}同学,邮件地址:{1},邮件内容:{2}发送邮件成功";
        System.out.println(MessageFormat.format(outputContent, mail.getName(), mail.getEmailAddress(), mail.getContent()));
    }

    public static void saveOriginMailRecord(Mail mail) {
        System.out.println("存储originMail记录,originMail:" + mail.getContent());
    }
}

public class Test {
    public static void main(String[] args) throws CloneNotSupportedException {
        Mail mail = new Mail();
        mail.setContent("初始化模板");
        System.out.println("初始化mail:"+mail);
        for(int i = 0;i < 10;i++){
            Mail mailTemp = (Mail) mail.clone();
            mailTemp.setName("姓名"+i);
            mailTemp.setEmailAddress("姓名"+i+"@imooc.com");
            mailTemp.setContent("恭喜您，此次活动中奖了");
            MailUtil.sendMail(mailTemp);
            System.out.println("克隆的mailTemp:"+mailTemp);
        }
        MailUtil.saveOriginMailRecord(mail);
    }
}

控制台输出：

3.源码

Object 的clone（）方法

protected native Object clone() throws CloneNotSupportedException;

arraylist

public class ArrayList extends AbstractList
        implements List, RandomAccess, Cloneable, java.io.Serializable
 。。。。。。。。。。
            public Object clone() {
        try {
            @SuppressWarnings("unchecked")
                ArrayList v = (ArrayList) super.clone();
            v.elementData = Arrays.copyOf(elementData, size);
            v.modCount = 0;
            return v;
        } catch (CloneNotSupportedException e) {
            // this shouldn't happen, since we are Cloneable
            throw new InternalError();
        }
    }

hashmap

public class HashMap
    extends AbstractMap
    implements Map, Cloneable, Serializable
{


public Object clone() {
    HashMap result = null;
    try {
        result = (HashMap)super.clone();
    } catch (CloneNotSupportedException e) {
        // assert false;
    }
    if (result.table != EMPTY_TABLE) {
        result.inflateTable(Math.min(
            (int) Math.min(
                size * Math.min(1 / loadFactor, 4.0f),
                // we have limits...
                HashMap.MAXIMUM_CAPACITY),
           table.length));
    }
    result.entrySet = null;
    result.modCount = 0;
    result.size = 0;
    result.init();
    result.putAllForCreate(this);

    return result;
}