享元模式

享元模式的核心是共享对象，目的是节省内存开销，分为三个场景，共享对象的内部状态、共享对象的工厂函数、共享对象的外部函数。以共享单车为例，如下

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// 内部状态
abstract class BikeFlyWeight{
    protected state:number = 0; // 0为未使用，1为使用中
    abstract ride(userName:string):void;
    public getState():number{
        return this.state;
    }
    public back(){
        this.state = 0;
    }
}

// 外部状态
class MoBikeFlyWeight extends BikeFlyWeight{
    private bikeId:string = '';
    
    constructor(bikeId:string){
        super();
        this.bikeId = bikeId;
    }

    ride(userName:string):void{
        this.state = 1;
        console.log(`${userName}骑${this.bikeId}号自行车`);
    }
}

// 共享对象的工厂函数
class BikeFlyWeightFactory{
    private static instance:BikeFlyWeightFactory = new BikeFlyWeightFactory();
    private pool:Set<BikeFlyWeight> = new Set<BikeFlyWeight>();
    private constructor(){
        for(let i = 0;i<2;i++){
            let bikeId:string = Math.floor(Math.random()*100000).toString(26);
            this.pool.add(new MoBikeFlyWeight(bikeId));
        }
    }

    public static getInstance():BikeFlyWeightFactory{
        return BikeFlyWeightFactory.instance;
    }

    public getBike():BikeFlyWeight|null{
        let resultBike:BikeFlyWeight = null;
        for(let bike of this.pool){
            if(bike.getState() === 0){
                resultBike = bike;
                break;
            }
        }
        return resultBike;
    }
}

// 客户端
class FlyWeightPattern{
    public static main():void{
        let bike1:BikeFlyWeight = BikeFlyWeightFactory.getInstance().getBike();
        bike1.ride('Jonny');

        let bike2:BikeFlyWeight = BikeFlyWeightFactory.getInstance().getBike();
        bike2.ride('Candy');
        bike2.back();

        let bike3:BikeFlyWeight = BikeFlyWeightFactory.getInstance().getBike();
        bike3.ride('Amy');

        console.log(bike2===bike3);  //是同一辆单车

        bike3.back();

        console.log(bike1===bike3);    //不是同一辆单车
    }
}

FlyWeightPattern.main();