java - 将数组数据输入到与另一个类中的另一个方法不同的类中的方法中

Question

这些类旨在协同工作以产生如下输出:/image/FPYwn.png我有一个逻辑错误，不允许我为显示和/或声明为 0 的变量生成输出和数据。我已经拼命工作了几个小时试图修复这个错误——但没有成功。如果有人能够告诉我如何解决代码中的问题以产生我想要的输出，我将非常感激。

这就是类(class)

/**
 * This class instantiates car objects with ten private instance variables.
 * It contains eight mutator methods to calculate mi/gal, distance (mi), gal/mi,
 * total cost; minimum/maximum, total, and annual values for these variables within a car object.
 * There are getter methods for each private instance variable.
 *
 * @author A. Mackey
 * @version 01/02/14
 */
public class AnnualFuelUse
{
    //private instance variables
    private double gallonsUsed, pricePerGallon, totalCost,
                   minSpeed, maxSpeed,
                   minVariable, maxVariable, minMaxVariable,
                   galPerMi, miPerGal,
                   startingMiles, endingMiles, distance,
                   totalVariable[], totalValue;

    //constructor with two parameters
    AnnualFuelUse(int FillUpNumber, double eMiles, double sMiles, double galsUsed, double pricePerGal)
    {
        startingMiles = sMiles;
        endingMiles = eMiles;
        gallonsUsed = galsUsed;
        pricePerGallon = pricePerGal;
    }

    //mutator method which calculates the distance drive
    public void calcDistance()
    {
        distance = endingMiles - startingMiles;
    }

    //getter method to return the value of distance traveled by the object on one trip
    public double getDistance()
    {
        return distance;
    }

    //mutator method which calculates gallons used per mile driven
    public void calcMPG(double dist, double gallons)
    {
        miPerGal = dist / gallons;
    }

    //getter method to return the value of the miles per gallon of the object on one trip
    public double getMPG()
    {
        return miPerGal;
    }

    //mutator method which calculates miles driven per gallons used
    public void calcGPM(double gallons, double dist)
    {  
        galPerMi = gallons / dist;
    }

    //getter method to return the value of the gallons per mile of the object on one trip
    public double getGPM()
    {
        return galPerMi;
    }

    //mutator method which calculates total cost of filling up
    public void totalCost()
    {
        totalCost = pricePerGallon * gallonsUsed;
    }

    //getter method to return the value of the total gasoline purchases on one trip
    public double getTotalCost()
    {
        return totalCost;
    }

    //mutator method which calculates the minimum value of a given array
    public void min(double minMaxVariable[])
    {
        minVariable = Double.MAX_VALUE;
        for(int i = 0; i < minMaxVariable.length; i ++)
        {
            if((minMaxVariable[i]) < minVariable)
            {    
                minVariable = minMaxVariable[i];
            }
        }
    }

    //getter method to return the minimum value of a given array
    public double getMin()
    {
        return minVariable;
    }

    //mutator method which calculates the minimum value of a given array
    public void max(double minMaxVariable[])
    {
        maxVariable = Double.MIN_VALUE;
        for(int i = 0; i < minMaxVariable.length; i ++)
        {
            if((minMaxVariable[i]) > maxVariable)
            {
                maxVariable = minMaxVariable[i];
            }
        }
    }

    //getter method to return the minimum value of a given array
    public double getMax()
    {
        return maxVariable;
    }

    //mutator method which calculates the total value of a given array
    public void totalOf(double totalVariable[])
    {
        totalValue = 0;
        for(double newValue : totalVariable)
        {
            totalValue += newValue;
        }
    }

    //getter method to return the total value of a given array
    public double getTotalOf()
    {
        return totalValue;
    }
}

及其测试器类

/**
 * This class tests the AnnualFuelUse class.
 *
 * An array of car objects is created to hold some of the private instance variables.
 *
 * A for loop is used to call the variables' methods on each object.
 * A second for loop is used to print an output header identifying the variables for the instance
 * A third for loop is used to print the values of the instance variables for each object.
 *
 * @author A. Mackey
 * @version 01/02/14
 */
public class AnnualFuelUseTester
{
    //main method
    public static void main(String[] args)
    {
        //declaring and initialising variables
        String header = "Annual Gas Mileage Calculations",
               headerLine = "===============================";
        String[] headerInfo = { "Fill Up" , "   Days" , "    Start Miles" , "   End Miles" , "Distance" , "Gallons" , "     Price" , "Cost" , "  Miles/Gal" , "Gal/Mile" };
        int[] fillUpNumber = {1, 2, 3, 4},
              daysSinceFill = {1, 4, 8, 13};
        double[] startMiles = {24963, 25437, 25937, 26221},
                 endMiles = { 25437, 25937, 26221, 26794},
                 gallonsUsed = { 21.4, 21.2, 12.2, 23.7},
                 milesPerGallon = new double[startMiles.length],
                 gallonsPerMile = new double[startMiles.length],
                 pricePerGallon = {3.52, 3.45, 3.39, 3.41},
                 totalCost = new double[startMiles.length],
                 distance = new double[startMiles.length];
        int minDistance,
            maxDistance,
            totalDistance,
            annualDistance;
        double minMPG, minCost,
               maxMPG, maxCost,
               totalGallonsUsed, totalCostSum,
               annualGallonsUsed, annualCost, annualMPG;

        //initialization of array of objects
        AnnualFuelUse[] car = {new AnnualFuelUse(fillUpNumber[0], endMiles[0], startMiles[0], gallonsUsed[0], pricePerGallon[0]),
                               new AnnualFuelUse(fillUpNumber[1], endMiles[1], startMiles[1], gallonsUsed[1], pricePerGallon[1]),
                               new AnnualFuelUse(fillUpNumber[2], endMiles[2], startMiles[2], gallonsUsed[2], pricePerGallon[2]),
                               new AnnualFuelUse(fillUpNumber[3], endMiles[3], startMiles[3], gallonsUsed[3], pricePerGallon[3])};

        //call methods  
        for(int index = 0; index < car.length; index++)
        {
            distance[index] = car[index].getDistance();
            milesPerGallon[index] = car[index].getMPG();
            gallonsPerMile[index] = car[index].getGPM();
            totalCost[index] = car[index].getTotalCost();
        }

        //I desire to invoke the methods which relate to these particular variables in order to define them
        minDistance = 0;
        minMPG = 0;
        minCost = 0;
        maxDistance = 0;
        maxMPG = 0;
        maxCost = 0;
        totalDistance = 0;
        totalGallonsUsed = 0;
        totalCostSum = 0;
        annualDistance = 0;
        annualGallonsUsed = 0;
        annualCost = 0;
        annualMPG = 0;

        //print results
        System.out.printf("%74s%n", header);
        System.out.printf("%74s%n", headerLine);

        for(String info : headerInfo)
        {
            System.out.print(info + "\t");
        }

        System.out.println("\n=========================================================================================================================");

        for(int index = 0; index < car.length; index++)
        {
            System.out.printf("%4d%10d%14.0f%14.0f%12.0f%16.1f%11.2f%12.2f%12.2f%13.3f%n", fillUpNumber[index], daysSinceFill[index], startMiles[index], endMiles[index], distance[index], gallonsUsed[index], pricePerGallon[index], totalCost[index], milesPerGallon[index], gallonsPerMile[index]);
        }

        System.out.println("=========================================================================================================================\n");

        System.out.printf("Minimum:%46d%27.2f%24.2f%n", minDistance, minMPG, minCost);
        System.out.printf("Maximum:%46d%27.2f%24.2f%n%n", maxDistance, maxMPG, maxCost);
        System.out.printf("Totals:%47d%16.1f%35.2f%n", totalDistance, totalGallonsUsed, totalCostSum);
        System.out.printf("Annual Projection:%36d%16.1f%11.2f%24.2f%n", annualDistance, annualMPG, annualGallonsUsed, annualCost);
    }
}

感谢您的帮助，谢谢。

编辑(美国东部时间 2014 年 1 月 3 日 03:00)

pastebin.com/BRJunSvS 和pastebin.com/kRRb0dmu 知道为什么我的 MPG 不是预计的年平均值吗？？？

Answer 1

距离、成本、每加仑英里数和每英里加仑数字段尚未初始化，因为您尚未调用任何方法来计算这些值。

无论如何，我认为存储基于其他实例变量计算的任何值没有多大意义。为什么不直接在调用 getDistance() 时计算距离，然后返回计算值呢？这样您就可以少维护一个字段。

这又是你的类，这次删除了一些实例变量和 setter，以及一些更改的 getter。我擅自将您的 min、max 和 totalOf 方法更改为静态方法。我不知道这是否是一个好的做法，但它们似乎不需要访问实例级变量或方法。

public class AnnualFuelUse
{
    //private instance variables
    private double gallonsUsed, pricePerGallon, startingMiles, endingMiles;

    //constructor with two parameters
    AnnualFuelUse(int FillUpNumber, double eMiles, double sMiles, double galsUsed, double pricePerGal)
    {
        startingMiles = sMiles;
        endingMiles = eMiles;
        gallonsUsed = galsUsed;
        pricePerGallon = pricePerGal;
    }

    //getter method to return the value of distance traveled by the object on one trip
    public double getDistance()
    {
        return endingMiles - startingMiles;
    }

    //getter method to return the value of the miles per gallon of the object on one trip
    public double getMPG()
    {
        return getDistance() / gallonsUsed;
    }

    //getter method to return the value of the gallons per mile of the object on one trip
    public double getGPM()
    {

        return gallonsUsed / getDistance();
    }

    //getter method to return the value of the total gasoline purchases on one trip
    public double getTotalCost()
    {
        return pricePerGallon * gallonsUsed;
    }

    //mutator method which calculates the minimum value of a given array
    public static double min(double minMaxVariable[])
    {
        double minVariable = Double.MAX_VALUE;
        for(int i = 0; i < minMaxVariable.length; i ++)
        {
            if((minMaxVariable[i]) < minVariable)
            {    
                minVariable = minMaxVariable[i];
            }
        }
        return minVariable;
    }

    //mutator method which calculates the minimum value of a given array
    public static double max(double minMaxVariable[])
    {
        double maxVariable = Double.MIN_VALUE;
        for(int i = 0; i < minMaxVariable.length; i ++)
        {
            if((minMaxVariable[i]) > maxVariable)
            {
                maxVariable = minMaxVariable[i];
            }
        }
        return maxVariable;
    }

    //mutator method which calculates the total value of a given array
    public static double totalOf(double totalVariable[])
    {
        double totalValue = 0;
        for(double newValue : totalVariable)
        {
            totalValue += newValue;
        }
        return totalValue;
    }
}

这应该可以处理表格上部的零。至于最小值、最大值和总值，它们显然将为零，因为您已经这样设置了它们。假设您已将上述方法设为静态，您可以这样调用它们。请注意由于 min、max 和 totalOf 返回 double 类型的值而进行的转换。

minDistance = (int)AnnualFuelUse.min(distance);
minMPG = AnnualFuelUse.min(milesPerGallon);
minCost = AnnualFuelUse.min(totalCost);
maxDistance = (int)AnnualFuelUse.max(distance);
maxMPG = AnnualFuelUse.max(milesPerGallon);
maxCost = AnnualFuelUse.max(totalCost);
totalDistance = (int)AnnualFuelUse.totalOf(distance);
totalGallonsUsed = AnnualFuelUse.totalOf(gallonsUsed);
totalCostSum = AnnualFuelUse.totalOf(totalCost);