java - 我得到必需的类型 : Double and Provided type: Void

Question

这是我的代码。如果你转到 System.out.printl("欧洲战斗机台风要飞行 4.2 小时，需要 "+ (Double.toString(calculateGallons(v:4.2)) + "加仑燃料"));您会看到我在围绕错误的括号一侧放置了两个破折号/连字符，在本例中为 (calculateGallons(v:4.2))。

package com.company;

class Aircraft1 {
    int passengers;         // Number of people on board
    int cruiseSpeed;        // Miles per hour
    double fuelCapacity;    // Gallons
    double fuelBurnRate;    // Gallons per hour

    // Method to calculate aircraft endurance

    double calculateEndurance() { // Function for aircraft
        double endurance;

        endurance = fuelCapacity / fuelBurnRate;

        return endurance;

    }


    }

public class Main1 {

            public static void main(String[] args) {


                double EuroFighterTyphoonEndurance; // Variable for F15 Fighter Endurance
                double F15_FighterEndurance; // Variable for F15 Fighter Endurance

                Aircraft EuroFighterTyphoon = new Aircraft();      // Creates object of class aircraft
                Aircraft F15_Fighter = new Aircraft();              // Creates object of class aircraft

                EuroFighterTyphoon.cruiseSpeed = 1550;   // Miles per hour
                EuroFighterTyphoon.passengers = 1;       // Number of people on board
                EuroFighterTyphoon.fuelBurnRate = 9.5;   // Gallons per hour
                EuroFighterTyphoon.fuelCapacity = 56.6;  // Gallons

                F15_Fighter.cruiseSpeed = 1875;  // Miles per hour
                F15_Fighter.passengers = 1;      // Number of people on board
                F15_Fighter.fuelBurnRate = 9.5;  // Gallons per hour
                F15_Fighter.fuelCapacity = 56.6; // Gallons

                System.out.println("For Eurofighter Typhoon to fly for 4.2 hours, it takes: " + (Double.toString--(calculateGallons(4.2))-- + " gallons of fuel"));

                System.out.println("Euro Fighter Typhoon Endurance is: " + EuroFighterTyphoon.calculateEndurance());

                double enduranceF15_Fighter = F15_Fighter.calculateEndurance();

                System.out.println("F15 Fighter Endurance is: " + F15_Fighter.calculateEndurance());
    }

    public static void calculateGallons(double v) {
    }
}

Answer 1

您正在调用Double.toString(calculateGallons(4.2))。
Double.toString 方法需要 Double 作为参数，但是，您的 calculateGallons() 方法返回 void，因此会出现错误。

您应该让 calculateGallons 返回一个 double 值，这样就可以了