Question

How to calculate the distance of speed

Asked by: gkilgore

I need someone to critque the attached program.  The program is support to ask the user to enter Air, Water or Steel and the distance that sound wave will travel.  The program should also display the amount of time it will take to travel using the following formula:

Air : time = distance / 1100
Water: time = distance / 4900
Steel: time = distance / 16400

I feel that an if statement should be included, but not really sure.  
Also, my program changed the formula, which may be incorrect.

Any assistance provided will be appreciated.

import java.util.Scanner;
import javax.swing.JOptionPane;
import java.text.DecimalFormat;
 
 
public class Switch
{
	public static void main(String[] args)
	{
		String input;
		char medium;
		double Air = 00.00;
		double Water = 00.00;
		double Steel = 00.00
		double Time = 00.00;
		double distance = 00.00;
		
			Scanner keyboard = new Scanner(System.in);
		
			System.out.println("Enter A for air, W for water and S for steel:");
			
			DecimalFormat formatter = new DecimalFormat("0.00");
 
					
		input = keyboard.nextLine();
		medium = input.charAt(0);
		
		input = JOptionPane.showInputDialog("Enter distance of air ");
		Air = Double.parseDouble(input);
		
				Air = Air / 1100;
 
		input = JOptionPane.showInputDialog("Enter water ");
		Water = Double.parseDouble(input);
		
				Water = Water / 4900;
		
		input = JOptionPane.showInputDialog("Enter steel ");
		Steel = Double.parseDouble(input);
		
				Steel = Steel / 16400;
 
		switch(medium)
		{
			case 'a':
			case 'A':
				System.out.println("Rate of Air " + Air);
				break;
			case 'w':	
			case 'W':
				System.out.println("Rate of Water " + Water);	
				break;
			case 's':	
			case 'S':
				System.out.println("Rate of Steel " + Steel);
				break;
			default:
				System.out.println("Invalid choice. ");
		}
	}
}

                                  
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Asked On
2009-06-22 at 08:58:18ID24511613
Tags

java

Topic

New to Java Programming

Participating Experts
2
Points
500
Comments
3

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Answers

 

by: humanonomicsPosted on 2009-06-22 at 09:28:32ID: 24684030

Why not try the following ?


import java.util.Scanner;
 
import javax.swing.JOptionPane;
 
 
public class Switch
{
        public static void main(String[] args)
        {
                String input;
                char medium;
                double Air = 00.00;
                double Water = 00.00;
                double Steel = 00.00;
                
                Scanner keyboard = new Scanner(System.in);
                
                System.out.print("Enter A for air, W for water and S for steel:");
                        
                input = keyboard.nextLine();
                medium = input.charAt(0);
                switch(medium)
                {
                        case 'a':
                        case 'A':
		                        	 input = JOptionPane.showInputDialog("Enter distance of air ");
		                             Air = Double.parseDouble(input);
                             
                                     Air = Air / 1100;
                                System.out.println("Rate of Air " + Air);
                                break;
                        case 'w':       
                        case 'W':
                            input = JOptionPane.showInputDialog("Enter water ");
                            Water = Double.parseDouble(input);
                            
                                            Water = Water / 4900;                        	
                                System.out.println("Rate of Water " + Water);   
                                break;
                        case 's':       
                        case 'S':
                            input = JOptionPane.showInputDialog("Enter steel ");
                            Steel = Double.parseDouble(input);
                            
                                            Steel = Steel / 16400;
                                     	
                                System.out.println("Rate of Steel " + Steel);
                                break;
                        default:
                                System.out.println("Invalid choice. ");
                }
        }
}

                                              
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by: mwvisa1Posted on 2009-06-22 at 09:45:41ID: 24684164

You can additionally make the input string upper or lower case so you only have to worry about character 'A', 'S', and 'W' or 'a', 's', and 'w' but not combination thereof.

Also for tighter code, you could create a function that displays prompt, parses to double (including any error handling if doesn't parse), calculates time based on distance entered and speed of medium and returns.  That way any logic changes would only need to be done in one place.

 

by: mwvisa1Posted on 2009-06-22 at 10:00:55ID: 24684305

Here is a sample of what I mean.  You will probably want to invest more time into handling exceptional inputs.  I have shown how to handle invalid numbers for distance as an example.

import java.text.DecimalFormat;
import java.util.Scanner;
 
import javax.swing.JOptionPane;
 
public class Switch {
	public static void main(String[] args) {
		char medium;
		Scanner keyboard = new Scanner(System.in);
 
		System.out.print("Enter A for air, W for water and S for steel:");
		medium = keyboard.nextLine().toUpperCase().charAt(0);
 
		switch (medium) {
		case 'A':
			displayRateOfMedium("Air", 1100);
			break;
		case 'w':
		case 'W':
			displayRateOfMedium("Water", 4900);
			break;
		case 's':
		case 'S':
			displayRateOfMedium("Steel", 16400);
			break;
		default:
			System.out.println("Invalid medium chosen!");
		}
	}
 
	static final DecimalFormat formatter = new DecimalFormat("0.00");
 
	static void displayRateOfMedium(String medium, double speed) {
		String input = 
			JOptionPane.showInputDialog(
				String.format("Enter distance of %1s: ", medium)
			);
		try {
			double distance = Double.parseDouble(input);
			System.out.println(String.format("Rate of %1s: %2s.", medium,formatter.format(distance / speed)));
		} catch (NumberFormatException nfe) {
			displayRateOfMedium(medium, speed);
		}
	}
}

                                              
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