Question

import java.util.Scanner;

public class MPGMain
{

   public static void main(String[] args)
   {
       Scanner input = new Scanner(System.in);
      
       Mileage mileage = new Mileage();
      
       System.out.println("Enter your miles: ");
       mileage.setMiles(input.nextDouble());
      
       System.out.println("Enter your gallons: ");
       mileage.setGallons(input.nextDouble());
      
       System.out.printf("MPG : %.2f",mileage.getMPG());
      
   }

}
public class Mileage
{
   private double miles;
   private double gallons;
   public double getMiles()
   {
       return miles;
   }
  
   public void setMiles(double miles)
   {
       this.miles = miles;
   }
  
   public double getGallons()
   {
       return gallons;
   }
  
   public void setGallons(double gallons)
   {
       this.gallons = gallons;
   }
  
   public double getMPG()
   {
       return getMiles() / getGallons();
   }
  
  
}

You will need to add two more classes to the Java Project. One called Distance and one called Speed. Similar to Mileage, Distance will have two private member variables, speed and time (both doubles); Speed will have two private member variables distance and time (again both are doubles). They will need sets and gets (also called accessors and mutators). Distance should have one more method called getDistance that performs the math calculation and returns the double totalDistance. Speed should have one more method called getMPH that performs the math calculation and returns the double mph Add a menu like the following to MPGMain: Enter 1 to Determine Miles-per-Gallon Enter 2 to Determine Distance Enter 3 to Determine Miles-per-Hour Enter 4 to Exit The program should switch on the user’s choice. The program should continue until the user enters 4. If the user enters a number greater than 4 or less than 1 the program should display an error message and prompt the user to reenter a number between 1 and 4. The program will continue to display the error message allowing the user to reenter their choice until they enter a number within the correct range. Each case in the switch statement should create an instance of the appropriate class (for example, case 1: Mileage, case 2: Distance, case 3: Speed), and set the variable values using the set methods of the class. Each case statement should also display the results of the appropriate mathematical calculations by calling the getMPG, getDistance, or getMPH methods.(This is my starting code plus setters and getters for distance and speed)

Answer 1

/*The java program that prompts user to enter a menu choice . The program checks if user input is valid or not. If inpu is valid the prompt for the corresponding the input values and find the results otherwise print the message INVALID INPUT . The program continues till user enters 4 to exit the program.
* */

//Main.java
import java.util.Scanner;
public class Main
{
   private static Scanner input = new Scanner(System.in);
   public static void main(String[] args)
   {

       int choice;
       boolean run=true;

       //Declare variables of Mileage,Distance and Speed class
       Mileage mileage =null;
       Distance distance=null;
       Speed speed=null;
      
       /*Continue till user enters 4 to exit*/
       while(run)
       {
           //calling menu method
           choice=menu();
           switch (choice)
           {
           case 1:
               //Create an instanace of Mileage class
               mileage=new Mileage();
               System.out.println("Enter your miles: ");
               double miles=Double.parseDouble(input.nextLine());
               mileage.setMiles(miles);
              
               System.out.println("Enter your gallons: ");
               double gallons=Double.parseDouble(input.nextLine());
               mileage.setGallons(gallons);
              
               System.out.printf("MPG : %.2f",mileage.getMPG());
               break;
              
           case 2:
               //Create an instanace of Distance class
               distance=new Distance();
               System.out.println("Enter your speed in miles/hour: ");
               double inputspeed=Double.parseDouble(input.nextLine());
               distance.setSpeed(inputspeed);
              
               System.out.println("Enter your time in hours: ");
               double inputhours=Double.parseDouble(input.nextLine());
               distance.setTime(inputhours);
              
               System.out.printf("Distance : %.2f miles ",distance.getDistance());
               break;
              
           case 3:
               //Create an instanace of Speed class
               speed=new Speed();
               System.out.println("Enter your distance in miles: ");
               double inputmiles=Double.parseDouble(input.nextLine());
               speed.setDistance(inputmiles);
              
               System.out.println("Enter your time in hours: ");
               double inputtime=Double.parseDouble(input.nextLine());
               speed.setTime(inputtime);
               System.out.printf("Speed : %.2f miles/hours",speed.getSpeed());
               break;
              
           case 4:
               //exit from the program
               System.out.println("Bye!");
               run=false;
           }
       }
   }

   public static int menu()
   {
       int choice=0;
       do
       {
           System.out.println();
           System.out.println("Enter 1 to Determine Miles-per-Gallon ");
           System.out.println("Enter 2 to Determine Distance");
           System.out.println("Enter 3 to Determine Miles-per-Hour");
           System.out.println("Enter 4 to Exit");
           System.out.print("Enter your choice[1-4] : ");
           choice=Integer.parseInt(input.nextLine());
          
           if(choice<1 || choice>4)
               System.out.println("INVALID CHOICE");
          
       }while(choice<1 || choice>4);  
       return choice;   //return choice value
   } //end of the method ,menu
  
} //end of the class

Sample Output:

Enter 1 to Determine Miles-per-Gallon
Enter 2 to Determine Distance
Enter 3 to Determine Miles-per-Hour
Enter 4 to Exit
Enter your choice[1-4] : 5
INVALID CHOICE

Enter 1 to Determine Miles-per-Gallon
Enter 2 to Determine Distance
Enter 3 to Determine Miles-per-Hour
Enter 4 to Exit
Enter your choice[1-4] : 1
Enter your miles:
100
Enter your gallons:
10
MPG : 10.00
Enter 1 to Determine Miles-per-Gallon
Enter 2 to Determine Distance
Enter 3 to Determine Miles-per-Hour
Enter 4 to Exit
Enter your choice[1-4] : 2
Enter your speed in miles/hour:
10
Enter your time in hours:
10
Distance : 100.00 miles
Enter 1 to Determine Miles-per-Gallon
Enter 2 to Determine Distance
Enter 3 to Determine Miles-per-Hour
Enter 4 to Exit
Enter your choice[1-4] : 3
Enter your distance in miles:
10
Enter your time in hours:
5
Speed : 2.00 miles/hours
Enter 1 to Determine Miles-per-Gallon
Enter 2 to Determine Distance
Enter 3 to Determine Miles-per-Hour
Enter 4 to Exit
Enter your choice[1-4] : 4
Bye!