场景：ATM取钱

100面额 -> 50面额 -> 20面额 -> 10面额

接口类

/**
 * 取钱抽象类
 */
public interface IDrawing {
    boolean draw(Integer amount);
}

面额类

import java.util.function.Function;

// 面额类
public class MoneyPile implements IDrawing {
    /**
     * 面额
     */
    private Integer value;

    /**
     * 数量
     */
    private Integer quantity;

    /**
     * 下一面额处理
     */
    private IDrawing next;

    public MoneyPile(Integer value, Integer quantity, IDrawing next) {
        this.value = value;
        this.quantity = quantity;
        this.next = next;
    }

    @Override
    public boolean draw(Integer amount) {
        // 判断是否可以取
        Function<Integer,Boolean> canTake = (want) -> (want / this.value) > 0;
        while (canTake.apply(amount)) {
            if (quantity == 0 ) break;
            amount -= value;
            quantity -= 1;
        }
        if (amount <= 0) return true;
        if (next != null) return next.draw(amount);
        return false;
    }
}

ATM类

public class ATM implements IDrawing{
    private IDrawing hundred;
    private IDrawing fifty;
    private IDrawing twenty;
    private IDrawing ten;

    private IDrawing startPile;

    public ATM(IDrawing hundred, IDrawing fifty, IDrawing twenty, IDrawing ten) {
        this.hundred = hundred;
        this.fifty = fifty;
        this.twenty = twenty;
        this.ten = ten;
        this.startPile = hundred;
    }

    @Override
    public boolean draw(Integer amount) {
        return startPile.draw(amount);
    }
}

使用

public class Main {
    public static void main(String[] args) {
        MoneyPile ten = new MoneyPile(10, 2, null);
        MoneyPile twenty = new MoneyPile(20, 4, ten);
        MoneyPile fifty = new MoneyPile(50, 2, twenty);
        MoneyPile hundred = new MoneyPile(100, 1,fifty);
        ATM atm = new ATM(hundred, fifty, twenty, ten);
        boolean taked = atm.draw(300);
        if (taked){
            System.out.println("完成");
        }else {
            System.out.println("ATM钱不够了");
        }
    }
}