Java中的原型模式

原型模式简介

模式属于创建型模式，它提供了一种创建对象的最佳方式。
用于创建重复的对象，同时又能保证性能。
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

类Book实现Cloneable接口并重写clone方法

public class Book implements Cloneable {
    private String name;//书名
    private Date publishDate;//发布日期

    public Book() {
    }

    public Book(String name, Date publishDate) {
        this.name = name;
        this.publishDate = publishDate;
    }

    public String getName() {
        return name;
    }

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

    public Date getPublishDate() {
        return publishDate;
    }

    public void setPublishDate(Date publishDate) {
        this.publishDate = publishDate;
    }

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

    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", publishDate=" + publishDate +
                '}';
    }
}

测试类

public class Test {
    public static void main(String[] args) throws CloneNotSupportedException {
        String name = "Java 设计模式";
        Date publishDate = new Date();

        Book book = new Book(name, publishDate);
        //克隆出对象
        Book clone = (Book) book.clone();

        System.out.println(book);
        System.out.println(book.hashCode());
        System.out.println(clone);
        System.out.println(clone.hashCode());

        System.out.println("==================");

        publishDate.setTime(publishDate.getTime() + 2000);//修改时间
        System.out.println(book);
        System.out.println(book.hashCode());
        System.out.println(clone);
        System.out.println(clone.hashCode());

        /**
         * 测试结果：修改了时间，源对象和克隆的对象的时间，都发生了改变
         * Book{name='Java 设计模式', publishDate=Wed Dec 29 12:17:33 CST 2021}
         * 2093631819
         * Book{name='Java 设计模式', publishDate=Wed Dec 29 12:17:33 CST 2021}
         * 2074407503
         * ==================
         * Book{name='Java 设计模式', publishDate=Wed Dec 29 12:17:35 CST 2021}
         * 2093631819
         * Book{name='Java 设计模式', publishDate=Wed Dec 29 12:17:35 CST 2021}
         * 2074407503
         */
    }
}

测试结果

Book{name='Java 设计模式', publishDate=Wed Dec 29 12:17:33 CST 2021}
2093631819
Book{name='Java 设计模式', publishDate=Wed Dec 29 12:17:33 CST 2021}
2074407503
==================
Book{name='Java 设计模式', publishDate=Wed Dec 29 12:17:35 CST 2021}
2093631819
Book{name='Java 设计模式', publishDate=Wed Dec 29 12:17:35 CST 2021}
2074407503

深克隆

类Book实现Cloneable接口并重写clone方法

public class Book implements Cloneable {
    private String name;//书名
    private Date publishDate;//发布日期

    public Book() {
    }

    public Book(String name, Date publishDate) {
        this.name = name;
        this.publishDate = publishDate;
    }

    public String getName() {
        return name;
    }

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

    public Date getPublishDate() {
        return publishDate;
    }

    public void setPublishDate(Date publishDate) {
        this.publishDate = publishDate;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        Object obj = super.clone();
        Book book = (Book) obj;

        //将源对象的属性也进行克隆，即深克隆
        book.publishDate = (Date) book.publishDate.clone();
        return obj;
    }

    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", publishDate=" + publishDate +
                '}';
    }
}

测试类

public class Test {
    public static void main(String[] args) throws CloneNotSupportedException {
        String name = "Java 设计模式";
        Date publishDate = new Date();

        Book book = new Book(name, publishDate);
        //克隆出对象
        Book clone = (Book) book.clone();

        System.out.println(book);
        System.out.println(book.hashCode());
        System.out.println(clone);
        System.out.println(clone.hashCode());

        System.out.println("==================");

        publishDate.setTime(publishDate.getTime() + 2000);
        System.out.println(book);
        System.out.println(book.hashCode());
        System.out.println(clone);
        System.out.println(clone.hashCode());

        /**
         * 测试结果：修改了时间，源对象的时间，发生了改变，但克隆的对象的时间没有改变
         * Book{name='Java 设计模式', publishDate=Wed Dec 29 12:41:47 CST 2021}
         * 2093631819
         * Book{name='Java 设计模式', publishDate=Wed Dec 29 12:41:47 CST 2021}
         * 2074407503
         * ==================
         * Book{name='Java 设计模式', publishDate=Wed Dec 29 12:41:49 CST 2021}
         * 2093631819
         * Book{name='Java 设计模式', publishDate=Wed Dec 29 12:41:47 CST 2021}
         * 2074407503
         */
    }
}

测试结果

Book{name='Java 设计模式', publishDate=Wed Dec 29 12:41:47 CST 2021}
2093631819
Book{name='Java 设计模式', publishDate=Wed Dec 29 12:41:47 CST 2021}
2074407503
==================
Book{name='Java 设计模式', publishDate=Wed Dec 29 12:41:49 CST 2021}
2093631819
Book{name='Java 设计模式', publishDate=Wed Dec 29 12:41:47 CST 2021}
2074407503

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