備忘錄模式

備忘錄模式UML.png

class Originator{
    private int stateA = 0;
    private int stateB = 0;
    private int stateC = 0;
    
    public Memoto createMemoto(){
        Memoto memoto = new Memoto();
        memoto.setStateA(stateA);
        memoto.setStateB(stateB);
        memoto.setStateC(stateC);
    }
    
    public void restore(Memoto memoto){
        this.stateA = memoto.getStateA();
        this.stateB = memoto.getStateB();
        this.stateC = memoto.getStateC();
    }
    
    public void change(){
        stateA = 1;
        stateB = 2;
        stateC = 3;
    }
    
    public void showData(){
        System.out.println(stateA+"=="+stateB+"=="+stateC);
    }
    
}

原始類

class Memoto{
    private int stateA;
    private int stateB;
    private int stateC;
    
    public int getStateA(){
        return this.stateA;
    }
    public int getStateB(){
        return this.stateB;
    }
    public int getStateC(){
        return this.stateC;
    }
    public void setStateA(int a){
        this.stateA = a;
    }
    public void setStateB(int b){
        this.stateB = b;
    }
    public void setStateC(int c){
        this.stateC = c;
    }
}   

數(shù)據(jù)bean類

class Caretaker{
    Memoto memoto;
    public Memoto restoreMemoto(){
        return this.memoto;//恢復(fù)數(shù)據(jù)
    }
    
    public void storeMemoto(Memoto memoto){
        this.memoto = memoto;
    }
}

備忘錄對象，管理Memoto對象

class Cliten{
    public static void main(String args[]){
        Originator originator = new Originator();
        Caretaker caretaker = new Caretaker();
        originator.showData();//原始數(shù)據(jù)為 0 0 0 
        originator.change();//改變之后為 1 2 3
        caretaker.storeMemoto(originator.createMemoto());//存儲狀態(tài)
        //模擬下次登錄之后 重新開始
        Originator originatorNew = new Originator();    
        originatorNew.restore(caretaker.restoreMemoto());
        originatorNew.showData();//數(shù)據(jù)為 1 2 3
    }
}

客戶端模擬備忘錄模式。當(dāng)需要保存狀態(tài)的時候?qū)顟B(tài)存入Caretaker即可。Caretaker這里只是保存最后一次變化狀態(tài)，可以擴(kuò)展需求做的更豐富一些。

個人總結(jié)

例子比較簡單，僅僅只是備忘錄模式的原型。一句話概括就是備忘錄類會記住應(yīng)該記住的狀態(tài)，而存儲與恢復(fù)狀態(tài)在原始類中調(diào)用。
備忘錄模式在Android源碼里面例子，當(dāng)界面退居后臺或者由于內(nèi)存不足被干翻，在這之前會調(diào)用Activity中onSaveInstanceState方法保存狀態(tài)。當(dāng)界面再次出現(xiàn)在界面上時在onRestoreInstanceState方法中獲取之前保存的狀態(tài)。