java - 我收到了关于计算每小时英里数的作业，但我的运行程序似乎无法找到我的时间变量

Question

import java.util.Scanner;
import static java.lang.System.*;
import static java.lang.Math.*;

public class MPHRunner
{
    public static void main( String[] args )
    {
        Scanner keyboard = new Scanner(in);

        out.print("Enter the distance :: ");
        int dist = keyboard.nextInt();

        out.print("Enter the hours :: ");
        int hrs = keyboard.nextInt();

        out.print("Enter the minutes :: ");
        int mins = keyboard.nextInt();

        MilesPerHour test = new MilesPerHour(dist, hrs, mins,time);
        test.calcMPH(dist,time);
        test.print();
    }
}

当我尝试编译它时，它告诉我它无法找到变量time。它应该从其他类中找到，包括在下面......

import java.util.Scanner;
import static java.lang.System.*;
import static java.lang.Math.*;

public class MilesPerHour
{
    public int distance, hours, minutes;
    public double mph, time;

    public MilesPerHour()
    {
        setNums(0,0,0,0);
        mph=0.0;
    }

    public MilesPerHour(int dist, int hrs, int mins)
    {
        Scanner keyboard = new Scanner(System.in);
        out.println("enter distance");
        out.println("enter hours");
        out.println("enter minutes");
    }

    public void setNums(int dist, int hrs, int mins, double time)
    {
        distance = dist;
        hours = hrs;
        minutes = mins;
        time = ((hrs*60)+mins)/60;
    }

    public void calcMPH(int dist, double time)
    {
        mph = dist/time;
    }

    public void print(int mph, int dist, double time)
    {
        System.out.println("at "+mph+"MPH, you can go "+dist+" miles in "+time+"hours.");
    }
}

如果您能提供任何帮助，我们将不胜感激。

Answer 1

Scanner keyboard = new Scanner(in);

out.print("Enter the distance :: ");
int dist = keyboard.nextInt();

out.print("Enter the hours :: ");
int hrs = keyboard.nextInt();

out.print("Enter the minutes :: ");
int mins = keyboard.nextInt();

对象中发生的事情并不重要。在这里，您声明并定义 dist、hrs 和 mins，然后在下一行中:

MilesPerHour test = new MilesPerHour(dist, hrs, mins,time);

这不会编译，因为 time 尚未声明。

编辑

经过仔细检查，我注意到时间是根据其他字段计算的。在这种情况下，您不需要在参数中指定它，因为您不需要传入它。更改

public void setNums(int dist, int hrs, int mins, double time)

至

public void setNums(int dist, int hrs, int mins)

并在调用 setNums 方法时将其从参数列表中删除。

注意:如果您的老师无法诊断这里的编译问题，那么我肯定会将其报告给您的教育机构。这是新手程序员应该能够发现的。