《设计模式之禅》--备忘录扩展：clone方式的备忘录

需求：使用clone方式实现备忘录模式

发起人角色

public class Originator implements Cloneable {
    //内部状态
    private String state = "";

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    //创建一个备忘录
    public Originator createMemento() {
        return this.clone();
    }

    //恢复一个备忘录
    public void restoreMemento(Originator _originator) {
        this.setState(_originator.getState());
    }

    //克隆当前对象
    @Override
    protected Originator clone() {
        try {
            return (Originator) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return null;
    }
}

备忘录管理员角色

public class Caretaker {
    //发起人对象
    private Originator originator;

    public Originator getOriginator() {
        return originator;
    }

    public void setOriginator(Originator originator) {
        this.originator = originator;
    }
}

上面两项合并

public class Originator implements Cloneable {
    private Originator backup;
    //内部状态
    private String state = "";

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    //创建一个备忘录
    public void createMemento() {
        this.backup = this.clone();
    }

    //恢复一个备忘录
    public void restoreMemento() {
        //在进行恢复前应该进行断言，防止空指针
        this.setState(this.backup.getState());
    }

    //克隆当前对象
    @Override
    protected Originator clone() {
        try {
            return (Originator) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return null;
    }
}

调用

public class Client {
    public static void main(String[] args) {
        //定义发起人
        Originator originator = new Originator();
        //建立初始状态
        originator.setState("初始状态...");
        System.out.println("初始状态是：" + originator.getState());
        //建立备份
        originator.createMemento();
        //修改状态
        originator.setState("修改后的状态...");
        System.out.println("修改后状态是：" + originator.getState());
        //恢复原有状态
        originator.restoreMemento();
        System.out.println("恢复后状态是：" + originator.getState());
    }
}

结果

初始状态是：初始状态...
修改后状态是：修改后的状态...
恢复后状态是：初始状态

注意：