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Thread: Inputting then displaying through arrays? Urgent...

  1. #1
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    Default Inputting then displaying through arrays? Urgent...

    We were instructed to make a program where the user will input the Planets' name and mass then the data will be shown in a list (optional:the list should be in alphabetical order). We need to make some sort of menu where it displays 3 choices: Add Planet and Mass, View Record, and exit. I got a help from a friend with some parts except the part when displaying the data. it only says "null". it should look like:

    Planets and Their Masses:
    Earth 1234
    Jupiter 12345
    Mars 1234


    here's the code that needs editing...I've been searching on how to solve this and can't seem to find the solution, and I need to submit this 5 hours from now.

    import java.io.*;
    import java.util.Arrays;
    public class Planets
    {
        int a=0;
        int b=0;
        String[] planet = new String[8];
        double[] mass = new double[8];
        public static void main(String[]args)throws Exception
        {
            int choice;
     
     
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            do
            {
            System.out.println("[1] Add Planet/Mass");
            System.out.println("[2] View Records");
            System.out.println("[3] Exit");
            System.out.print("Select your choice: ");
            choice = Integer.parseInt(br.readLine());
            if (choice==1)
                {
                System.out.println("\n\n");
                Planets i = new Planets();
                i.Input();
                }
            if (choice==2)
                {
                System.out.println("\n");
                Planets v = new Planets();
                v.View();
                }
            }
     
            while (choice!=3);
            System.out.println("Thank You!");
        }
     
        public void Input()throws Exception
        {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter planet name: ");
        planet[0] = br.readLine();
     
     
        System.out.println("Enter mass: ");
        mass[0] = Double.parseDouble(br.readLine());
     
        }
     
        void View()
        {
            System.out.println("Planets and their Masses: ");
            System.out.println("" +planet[0] +mass[0]);
     
        }
     
     
    }
    Last edited by noia; May 8th, 2012 at 12:09 PM.


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Inputting then displaying through arrays? Urgent...

    Please Edit your post and wrap your code with[code=java]<YOUR CODE HERE>[/code] to get highlighting.

    Where is the "null" output? What variable has the null value?
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Inputting then displaying through arrays? Urgent...

    after adding the data, it will return to the menu, when the user chooses the "View Record" it should show a list of what data they had already entered, for example:

    Planets and Their Masses:
    Earth 1234
    Jupiter 12345
    Mars 1234

    but instead, these shows up:

    Planets and their Masses:
    null0.0

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Inputting then displaying through arrays? Urgent...

    That must mean that the program does not assign any values to the variables that are being printed. Look at the print statement for the variables that are being printed and then backtrack in the code to see why they do not have the values you want to see printed.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Inputting then displaying through arrays? Urgent...

    The problem is that when you add a planet, it is storing the values locally. When you try to view the data, you're creating a new instance of that object. To solve this, create a Planets object before the while loop, then add your planets to that object if they choose 1. If they choose 2, display the data.

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