java help

[F0xX]

can anyone help me figure out why i have a NullPointerException? thanks

import java.io.*;

 

public class NameSearchProgram {

  public static final int MAX_NAMES = 90000;

  public static int         numNames;

  public static String[]    names = new String[MAX_NAMES]; 

  

  // BubbleSort algorithm to sort all names by their length

  public static void bubbleSortByLength() {

    // ... Complete this ..

    for(int p=0; p < names.length; p++){

      if(names[p]==null){

        names[p]="expceptionNotFound";

        

        String storeName;

        

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

          for(int j=0; j<(names.length); j++){

            if(names.length() > names[i+1].length()){

              storeName = names;

              names = names[i+1];

              names[i+1] = storeName;

               }

        }

      }

      }

    }

    }

[MatthewEnderle]

it's easier to figure out with the code

[,,,,,,,,,,,,,,,,,,,,,,,,,,]

What's going on with this?

 

             }        }      }      }    }    }

[afyeung]

 

-SNIP-

 

From the code given, you have absolutely no Strings in your names array. The code is looping to locations in the array which contain nothing.

[Nineshadow]

When you do

  public static String[]    names = new String[MAX_NAMES]; 

You declare an array , but you do not instantiate its elements , which remain null.

 

You need to initialize the array elements.

[madknight3]

Please use code tags. You can add them in by using the <> icon above where you type your posts, or with your text like so

[code]Code goes here[/code]

[F0xX]

When you do

  public static String[]    names = new String[MAX_NAMES]; 

You declare an array , but you do not instantiate its elements , which remain null.

 

You need to initialize the array elements.

woops sorry later on in the code it takes the string array from a txt file

[PlutoNZL]

You should learn how to debug Java programs. When you're starting out with a new language you are going to run into a lot of problems like the one you just hit. Knowing how to debug your application will make solving your issues a lot faster and easier. Take a look at this: http://www.vogella.com/tutorials/EclipseDebugging/article.html

 

But to help with your question:

Lets add some strings to your names array and walk through bubbleSortByLength().

Lets say names contains a single name "Linus".

public static void bubbleSortByLength() {    // ... Complete this ..    for (int p = 0; p < names.length; p++) {        if (names[p] == null) {            names[p] = "expceptionNotFound";            String storeName;            for (int i = 0; i < (names.length); i++) {                for (int j = 0; j < (names.length); j++) {                    if (names[i].length() > names[i + 1].length()) { // i = 0, names[0] = "Linus", names[0 + 1] = null. You are trying to get the length() of a null string. That's what is causing your NullPointerException                        storeName = names[i];                        names[i] = names[i + 1];                        names[i + 1] = storeName;                    }                }            }        }    }}