Question

我试图制作一个MPG计算器，这里有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

我得到了什么：

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

我认为问题在于我的填充码，但我真是太愚蠢而且无法弄清楚......

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;
    }
}

请帮忙！我无法解决这个问题。

Answer 1

您的问题是，您永远不会推进Car对象的odometerReading属性（始终为零）。如果不初始化基元int，it defaults to 0。

快速解决方法是不将您的开始和结束里程设置为odometerReading属性，而是将startMiles等同于endMiles

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

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：

新车里程表读数：
  每加仑英里数16.875
  每加仑英里数16.875
  每加仑英里10.0   每加仑英里6.0英里

如果要将输出与预期匹配，请对主类进行以下更改：

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());
    }

为了支持这一点，您必须在Car课程中添加一个Getter方法，这样您就可以打印当前的里程数：

public int getEndMiles() {
    return endMiles;
}

新输出：

新车里程表读数：15
  每加仑英里数：16.875
  每加仑英里数：16.875
  每加仑英里数：10.0
  每加仑英里：6.0

Answer 2

您的odometerReading字段始终为0. resetMPG()也会将startMiles和endMiles重置为该值。

我想odometerReading字段应该始终显示应该在填充中设置的总里程数。对方法参数使用相同的名称会增加混淆。

简单的MPG逻辑

2 个答案: