java - 简单的 MPG 逻辑

Question

我正在尝试制作一个 MPG 计算器，这里是测试用例和预期结果:

我的测试员:

    Car auto = new Car(15);
    System.out.println("New car odometer reading: ");
    auto.fillUp(150,8);
    System.out.println("Miles per gallon" + auto.calculateMPG());
    System.out.println("Miles per gallon" + auto.calculateMPG());
    auto.resetMPG();
    auto.fillUp(350, 10);
    auto.fillUp(450, 20);
    System.out.println("Miles per gallon" + auto.calculateMPG());
    auto.resetMPG();
    auto.fillUp(603, 25.5);
    System.out.println("Miles per gallon" + auto.calculateMPG());

预期结果:

New car odometer reading: 15
Miles per gallon: 16.875
Miles per gallon: 16.875
Miles per gallon: 10.0
Miles per gallon: 6.0

我得到的:

New car odometer reading: 
Miles per gallon16.875
Miles per gallon16.875
Miles per gallon15.0
Miles per gallon23.647058823529413

我认为问题出在我的填充代码上，但我太笨了，无法弄清楚......

public class Car
{
    private int startMiles;
    private int endMiles;
    private double gallonsUsed;
    private int odometerReading;

    public Car(int odometerReading) {
        startMiles = odometerReading;
        endMiles = odometerReading;
    }

    public void fillUp (int odometerReading, double gallons) {
        endMiles = odometerReading;
        gallonsUsed = gallonsUsed + gallons;
    }

    public double calculateMPG() {
        double MPG = (endMiles-startMiles)/gallonsUsed;
        return MPG;
    }

    public void resetMPG() {
        gallonsUsed = 0;
        startMiles = odometerReading;
        endMiles = odometerReading;
    }
}

求助!我想不通。

Answer 1

您的问题是您永远不会提高 Car 对象的 odometerReading 属性(它始终为零)。当您不初始化原始 int 时，it defaults to 0 .

一个快速的解决方法是不要将您的开始和结束里程设置为您的 odometerReading 属性，而是让您的 startMiles 等于您的 endMiles

通过此更改，您还可以删除 int odometerReading 属性，因为它将不再被使用:

public class Car
{
    private int startMiles;
    private int endMiles;
    private double gallonsUsed;

    public Car(int odometerReading) {
        startMiles = odometerReading;
        endMiles = odometerReading;
    }

    public void fillUp (int odometerReading, double gallons) {
        endMiles = odometerReading;
        gallonsUsed = gallonsUsed + gallons;
    }

    public double calculateMPG() {
        double MPG = (endMiles-startMiles)/gallonsUsed;
        return MPG;
    }

    public void resetMPG() {
        gallonsUsed = 0;
        startMiles = endMiles;
    }
}

新输出:

New car odometer reading:
Miles per gallon16.875
Miles per gallon16.875
Miles per gallon10.0
Miles per gallon6.0

---

如果您希望输出符合您的预期，请对您的主类进行以下更改:

public static void main(String[] args) {
        Car auto = new Car(15);
        System.out.println("New car odometer reading: " + auto.getEndMiles());
        auto.fillUp(150,8);                            //^^Call a getter method
        System.out.println("Miles per gallon: " + auto.calculateMPG());
        System.out.println("Miles per gallon: " + auto.calculateMPG());
        auto.resetMPG();                  //^ just add a colon and space                  
        auto.fillUp(350, 10);
        auto.fillUp(450, 20);
        System.out.println("Miles per gallon: " + auto.calculateMPG());
        auto.resetMPG();
        auto.fillUp(603, 25.5);
        System.out.println("Miles per gallon: " + auto.calculateMPG());
    }

要支持这一点，您必须将 Getter 方法添加到您的 Car 类中，这样您就可以打印您当前的里程数:

public int getEndMiles() {
    return endMiles;
}

新输出:

New car odometer reading: 15
Miles per gallon: 16.875
Miles per gallon: 16.875
Miles per gallon: 10.0
Miles per gallon: 6.0