java - 输出为 "NaN"

Question

因此，我开发了一个类，该类应该被另一个类使用。我开发的类如下:

public class Car
{
private double milesPerGallon;
private double gas;

//Constructs a car with a given fuel efficiency
public Car(double milesPerGallon)
{
    gas = 0.0;
}

//Increases the amount of gas in the gas tank
public void addGas(double amount)
{
    gas = gas + amount;
}

//Decreases the amount of gas in the gas tank (due to driving and therefore consuming gas)
public void drive(double distance)
{
    gas = gas - (distance / milesPerGallon);
}

//Calculates range, the number of miles the car can travel until the gas tank is empty
public double range()
{
    double range;
    range = gas * milesPerGallon;
    return range;
}
}

应该使用我开发的类的类是:

public class CarTester
{
/**
 * main() method
 */
public static void main(String[] args)
{
    Car honda = new Car(30.0);      // 30 miles per gallon

    honda.addGas(9.0);              // add 9 more gallons
    honda.drive(210.0);             // drive 210 miles

    // print range remaining
    System.out.println("Honda range remaining: " + honda.range());

    Car toyota = new Car(26.0);      // 26 miles per gallon

    toyota.addGas(4.5);              // add 4.5 more gallons
    toyota.drive(150.0);             // drive 150 miles

    // print range remaining
    System.out.println("Toyota range remaining: " + toyota.range());
}
}

两个类都编译成功，但是当程序运行时，我得到输出“NaN”，它代表“不是数字”。我查了一下，据说当有一个数学过程试图除以零或类似的东西时，就会发生这种情况。我再说一遍，我并不是在寻找答案，而是在正确的方向上插入我可能犯下的错误，我将不胜感激(我确信这是一个非常小而愚蠢的错误)。谢谢!

Answer 1

在构造函数中保存您的 milesPerGallon 变量:

public Car(double milesPerGallon)
{
   this.milesPerGallon = milesPerGallon;
   gas = 0.0;
}