用java编写程序移动手机和座机是手机；手机是主类。设计一个座机类一个移动手机类和一个测试类。基本功能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。

座机类：

public class Telephone {
    private double callTime;  // 通话时长
    private double balance;   // 余额

    public Telephone(double balance) {
        this.balance = balance;
    }

    public double getCallTime() {
        return callTime;
    }

    public void setCallTime(double callTime) {
        this.callTime = callTime;
    }

    public double getBalance() {
        return balance;
    }

    public void setBalance(double balance) {
        this.balance = balance;
    }

    public double calculateCost() {
        return callTime * 0.2;  // 计算通话费用
    }

    public void recharge(double amount) {
        balance += amount;  // 充值
    }

    public void showBalance() {
        System.out.println("Your balance is: " + balance);
    }
}

移动手机类：

public class MobilePhone extends Telephone {
    public MobilePhone(double balance) {
        super(balance);
    }

    @Override
    public double calculateCost() {
        return getCallTime() * 0.5;  // 计算通话费用
    }
}

测试类：

public class Test {
    public static void main(String[] args) {
        Telephone telephone1 = new Telephone(100);
        telephone1.setCallTime(10);
        System.out.println("Cost of Telephone: " + telephone1.calculateCost());
        telephone1.recharge(50);
        telephone1.showBalance();

        MobilePhone mobilePhone1 = new MobilePhone(50);
        mobilePhone1.setCallTime(10);
        System.out.println("Cost of MobilePhone: " + mobilePhone1.calculateCost());
        mobilePhone1.recharge(20);
        mobilePhone1.showBalance();
    }
}

输出结果：

Cost of Telephone: 2.0
Your balance is: 150.0
Cost of MobilePhone: 5.0
Your balance is: 70.0
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