策略模式

public interface realprice {
    public double realprice(double a);
}

 public class common implements realprice {
    @Override
    public double realprice(double a) {
        return a;
    }
}

public class vip implements realprice {
    @Override
    public double realprice(double a) {
        return a*0.9;
    }
}

public class goldvip implements realprice{
    @Override
    public double realprice(double a) {
        return a*0.8;
    }
}

public class context {
    private double oneprice = 0;
    private double totalprice = 0;
    private realprice end = new common();

    public void moneynum(double a) {
        this.oneprice = a;
        totalprice += oneprice;
        if (totalprice <= 1000) {
            System.out.println("您应付的价格为：" + end.realprice(oneprice));
        } else if (totalprice >= 1000 && totalprice <= 2000) {
            end = new vip();
            System.out.println("您应付的价格为：" + end.realprice(oneprice));
        } else if (totalprice >= 2000 && totalprice <= 3000) {
            end = new goldvip();
            System.out.println("您应付的价格为：" + end.realprice(oneprice));
        }
    }
}

public class client {
     public static void main(String[] args) {
        context change=new context();
        change.moneynum(500);
        change.moneynum(500);
        change.moneynum(500);
        change.moneynum(500);
        change.moneynum(500);
        change.moneynum(500);
     }
}