抽象类示例

public abstract class Card {
    private String name;
    private double money;

    public abstract void pay(double money);

    public String getName() {
        return name;
    }

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

    public double getMoney() {
        return money;
    }

    public void setMoney(double money) {
        this.money = money;
    }
}

public class GoldCard extends Card{
    @Override
    public void pay(double money) {
        //  优惠后金额
        double rs = money * 0.8;
        double lastMoney = getMoney() - rs;

        System.out.println(getName() + "当前账户金额：" + getMoney()
            + "当前消费：" + rs + "元，当前剩余：" + lastMoney + "元"
        );

        setMoney(lastMoney);
    }
}

public class Test {
    public static void main(String[] args) {
        GoldCard c = new GoldCard();
        c.setMoney(10000.0);
        c.setName("张三");
        c.pay(300);
    }
}