Storing and accessing strings in Java (by using arrays)

Question

I'm trying to input a number of strings (song names) into an array. The program will then ask the user to name one of songs and tell the user what position that song was placed in the array.

Edit:

Thanks for the help guys. I've set both for loops to 0 and i'm still having trouble. I'm having various issues with the program. I'm getting the runtime errors of ArrayIndexOutOfBoundsException and NullPointerExeption.

What should I be doing to make it work?.

Thanks in advance to everyone.

Code:

import javax.swing.*; // import the swing library for I/O

class favsongs
{

   public static void main (String[] param)
{
      music();
      System.exit(0);

} // END main


/* ***************************************************
   Set up an array containing songs then find one asked for by the user
*/

public static void music()
{

   // Declare variables
   //
String key =""; //the thing looked for
int result = -1;// the position where the answer is found
String[] songs = new String[5];





// Ask for songs
for (p=0; p<=4; p++)
{   

         songs[p]=JOptionPane.showInputDialog("Song "+ p + "?");
    }

// Ask user for a song
key = JOptionPane.showInputDialog("Name a song and i'll tell you what position you placed it in.");

    for (int i=0; i<songs.length; i++)
    {

       if (songs[i].equals(key))
       {
          result = i;   
       }
       else // Error message
       {
       JOptionPane.showMessageDialog(null,"Error!!");
       break;
       }
    }
    // Tells user the name of the song and what position in the array it is in
   JOptionPane.showMessageDialog(null,"You placed " + key + " in position " + " " + result);

} // END music

 } // END class favsongs

ArrayIndexOutOfBoundsException and NullPointerExeption are runtime-exceptions so you don't get those from the compiler. — Bhesh Gurung
– Bhesh Gurung, Commented Nov 21, 2011 at 19:50

Jon Skeet · Accepted Answer · 2011-11-21 19:45:03Z

Look at this loop:

for (p=1; p<=4; p++)

Note that it starts at 1. So songs[0] will still have its default value of null. Now look at how you use the array:

for (int i=0; i<songs.length; i++)
{
   if (songs[p].equals(key))

Not only are you trying to use p here when I think you mean i, but either way will fail. Using p will access songs[5] which is out of bounds, and using i will call equals on songs[0] which is null.

Hopefully that's enough of a hint to get you going. A few other points:

Your "Sorry, What?" prompt is inside the loop. Did you mean it to be?
You should look at the Java naming conventions, both for capitalization and to give your methods more meaningful names
You should try to declare variables in as tight a scope as possible. You wouldn't have been able to make the mistake of using p at the wrong place if you'd declared it as part of the for loop.

ethan · Accepted Answer · 2011-11-21 19:45:57Z

0

// Ask for songs
for (p=1; p<=4; p++)
{      

     songs[p]=JOptionPane.showInputDialog("Song "+ p + "?");
}

this will leave songs[0] uninitialized. When you try to use it later you'll get a NullPointerException.

answered Nov 21, 2011 at 19:45

ethan

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Comments

dann.dev · Accepted Answer · 2011-11-21 19:46:35Z

0

First off, your loop to put songs into the is starting at 1, trying setting p=0, arrays go from zero to length -1. Try this and then see if it fixes the issue

answered Nov 21, 2011 at 19:46

dann.dev

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Comments

npinti · Accepted Answer · 2011-11-21 19:47:33Z

0

Your problem seems to be here:

for (p=1; p<=4; p++)
{  
    songs[p]=JOptionPane.showInputDialog("Song "+ p + "?");
}

In Java, array locations start at 0 and end at [arrayLength] - 1.

Doing like so should fix your problem:

for (p=0; p < song.length(); p++)
{  
    songs[p]=JOptionPane.showInputDialog("Song "+ p + "?");
}

This tutorial from Oracle should help you get started. You might also want to give a look at the ArrayList Class, which will allow you to dynamically add items to your list as shown in this simple tutorial.

answered Nov 21, 2011 at 19:47

npinti

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