1要求至少设计三个类一个座机类一个移动手机类一个测试类在测试类中需应用自己已经创建的功能模块的方法。2基本功能应包括：可以根据通话时长收取相应的费用同时具有充话费、显示余额的功能。3使用java编写程序

座机类：

public class Landline {
    private double pricePerMinute; //每分钟通话费用
    private double balance; //账户余额

    public Landline(double pricePerMinute, double balance) {
        this.pricePerMinute = pricePerMinute;
        this.balance = balance;
    }

    //充值话费
    public void recharge(double amount) {
        balance += amount;
        System.out.println("充值成功，当前余额为：" + balance);
    }

    //通话，并扣除相应的费用
    public void call(double duration) {
        double cost = duration * pricePerMinute;
        if (balance >= cost) {
            balance -= cost;
            System.out.println("通话成功，本次扣除费用为：" + cost + "，当前余额为：" + balance);
        } else {
            System.out.println("余额不足，请先充值");
        }
    }

    //显示余额
    public void showBalance() {
        System.out.println("当前余额为：" + balance);
    }
}

移动手机类：

public class MobilePhone {
    private double pricePerMinute; //每分钟通话费用
    private double balance; //账户余额

    public MobilePhone(double pricePerMinute, double balance) {
        this.pricePerMinute = pricePerMinute;
        this.balance = balance;
    }

    //充值话费
    public void recharge(double amount) {
        balance += amount;
        System.out.println("充值成功，当前余额为：" + balance);
    }

    //通话，并扣除相应的费用
    public void call(double duration) {
        double cost = duration * pricePerMinute;
        if (balance >= cost) {
            balance -= cost;
            System.out.println("通话成功，本次扣除费用为：" + cost + "，当前余额为：" + balance);
        } else {
            System.out.println("余额不足，请先充值");
        }
    }

    //显示余额
    public void showBalance() {
        System.out.println("当前余额为：" + balance);
    }
}

测试类：

public class Test {
    public static void main(String[] args) {
        Landline landline = new Landline(0.2, 10);
        MobilePhone mobilePhone = new MobilePhone(0.5, 20);

        //座机充值
        landline.recharge(5);
        //座机通话
        landline.call(30);
        //座机显示余额
        landline.showBalance();

        System.out.println("=========");

        //手机充值
        mobilePhone.recharge(10);
        //手机通话
        mobilePhone.call(15);
        //手机显示余额
        mobilePhone.showBalance();
    }
}
``