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Thread: Problem with lists

  1. #1
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    Default Problem with lists

    I have an assignment for college that involves placing randomly chosen words from a text file into a 2-d array. I have nearly completed ithowever I am having difficulty with a list of string type.

    What I have done so far is below, sorry its long...
    import java.util.Arrays;
    import java.util.List;
    import java.util.ArrayList;
    import java.io.*;
    import java.lang.Math;
     
    public class WordSearchPuzzle
    {
        private char[][] puzzle;
        private List<String> puzzleWords;
        private List<String> wordsForGrid;
        private int gridDimension;
        private char [] alphabet;
     
        public WordSearchPuzzle(List<String>userSpecifiedWords)
        {
            gridDimension = sizeOfGrid(puzzleWords);
            this.puzzle = new char[gridDimension][gridDimension];//grid is going to be a square
            this.puzzleWords=userSpecifiedWords;
     
        }
        public WordSearchPuzzle(String wordFile, int wordCount, int shortest, int longest)
        {
            int temp;
            if(shortest>longest)
            {
                temp=longest;
                longest=shortest;
                shortest=temp;
            }
            puzzleWords = loadWordsFromFile(wordFile,shortest,longest);
            for(int i=0;i<wordCount;i++)
            {
                int pos=(int)(Math.random()*puzzleWords.size());    
                wordsForGrid.add(puzzleWords.get(pos));            
            }
            int gridDimension = sizeOfGrid(puzzleWords);
            this.puzzle = new char[gridDimension][gridDimension];
            puzzleWords=wordsForGrid;
     
     
        }
        public int sizeOfGrid(List<String> puzzleWords)
        {
            double temp=0;
            int gridDimension;
            for(int i=0;i<puzzleWords.size();i++)
            {
                temp+=puzzleWords.get(i).length();
            }
            temp =Math.sqrt(temp);
            temp=(int)(temp*1.75);//scalling up by a factor of 1.75 as suggested;
            gridDimension=(int)(temp);
            return gridDimension;
        }
        /*public void fillGrid (List<String> puzzleWords)
        {
            for(int i=0;i<puzzleWords.size();i++)
            {
            }
     
        }*/
        private List<String> loadWordsFromFile(String wordFile, int shortest, int longest)
        {
            try
            {
                FileReader aFileReader = new FileReader(wordFile);
                BufferedReader aBufferReader = new BufferedReader(aFileReader);
                String lineFromFile;
                List <String>words=new ArrayList<String>();//would not let me create an empty List, created an ArrayList insead.
                lineFromFile = aBufferReader.readLine();
                int wordLength;
                while(lineFromFile!=null)
                {
                    wordLength=lineFromFile.length();
                    if(wordLength>=shortest&&wordLength<=longest)
                    {
                        words.add(lineFromFile);
                    }
                    lineFromFile=aBufferReader.readLine();
                }
                aBufferReader.close();
                aFileReader.close();
                return words;
            }
            catch (IOException x)
            {
                return null;
            }
        }
        public List<String> getWordSearchList()
        {
            return this.puzzleWords;       
        }
     
        public char[][]getPuzzleAsGrid()
        {
            int i;
            int j;
            alphabet =new char []{('a'),('b'),('c'),('d'),('e'),('f'),('g'),('h'),('i'),('j'),('k'),('l'),('m'),('n'),('o'),('p'),('q'),('r'),('s'),('t'),('u'),('v'),('w'),('x'),('y'),('z')};
     
            for(i=0;i<puzzle.length;i++)
            {
                for(j=0;j<gridDimension;j++)
                {
                    int randomChar = (int)(Math.random()*alphabet.length);
                    this.puzzle[i][j]=alphabet[randomChar];
                    System.out.print(puzzle[i][j]+"");
                }
                System.out.println();
            }
            return puzzle;
        }
        public String getPuzzleAsString()
        {   
            int i;
            int j;
            String puzzleString="";
            for(i=0;i<gridDimension;i++)
            {
                for(j=0;j<gridDimension;j++)
                {
                    puzzleString+=puzzle[i][j];
                }
                if(i==gridDimension)
                {
                    puzzleString+="\n";
                }
            }
            return puzzleString;
        }
        public void showWordSearchPuzzle()
        {
            generateWordSearchPuzzle();
            for(int i=0;i<puzzleWords.size();i++)
            {
                System.out.println(puzzleWords.get(i));
            }
        }
        public void generateWordSearchPuzzle()
        {
           int j=0;//to be used to check if the space where the current word is supposed to go is empty
           int i;//to be used to go through the list of words
           int k;//to be used to get the individual character from the current word
           int randomDirection;//determine which direction to place the word
           int randomRow;//starting position for word
           int randomCol;//starting position for word
           for(i=0;i<puzzleWords.size();)
           {
              randomDirection = (int)(Math.random()*4);
              randomRow=(int)(Math.random()*gridDimension);
              randomCol=(int)(Math.random()*gridDimension);
              int randomColTemp = randomCol;
              int randomRowTemp = randomRow;
              if(randomDirection==0)//word being placed to the right
              {
                  if(gridDimension-(randomCol+1)>=puzzleWords.get(i).length())
                  {
                      for(j=0;j<puzzleWords.get(i).length();j++)
                      {
                        if(puzzle[randomRow][randomColTemp]==0)
                        {
                            randomColTemp++;
                        }
                        else
                        j=puzzleWords.get(i).length()+1;//space is not empty,want to break the loop
                      }
                  }
                  if(j==puzzleWords.get(i).length())
                  {
                      for(k=0;k<puzzleWords.get(i).length();)
                      {
                          puzzle[randomRow][randomCol]=puzzleWords.get(i).charAt(k);
                          randomCol++;
                          k++;
                      }
                      i++;
                  }
              }
              if(randomDirection==1)//word being placed to the left)
              {
                  if(randomCol+1>=puzzleWords.get(i).length())
                  {
                      for(j=0;j<puzzleWords.get(i).length();j++)
                      {
                          if(puzzle[randomRow][randomColTemp]==0)
                          {
                              randomColTemp--;
                          }
                          else
                          j=puzzleWords.get(i).length()+1;
                      }
                  }
                  if(j==puzzleWords.get(i).length())
                  {
                      for(k=0;k<puzzleWords.get(i).length();)
                      {
                          puzzle[randomRow][randomCol]=puzzleWords.get(i).charAt(k);
                          randomCol--;
                          k++;
                      }
                      i++;
                  }
              }
              if(randomDirection==2)//word being placed vertically down
              {
                  if(gridDimension-(randomRow+1)>=puzzleWords.get(i).length())
                  {
                      for(j=0;j<puzzleWords.get(i).length();j++)
                      {
                          if(puzzle[randomRowTemp][randomCol]==0)
                          {
                              randomRowTemp++;
                          }
                          else
                          j=puzzleWords.get(i).length()+1;
                      }
                  }
                  if(j==puzzleWords.get(i).length())
                  {
                      for(k=0;k<puzzleWords.get(i).length();)
                      {
                          puzzle[randomRow][randomCol]=puzzleWords.get(i).charAt(k);
                          randomRow++;
                          k++;
                      }
                      i++;
                  }
              }
              if(randomDirection==3)//word being placed vertically up
              {
                  if(randomRow+1>=puzzleWords.get(i).length())
                  {
                      for(j=0;j<puzzleWords.get(i).length();j++)
                      {
                          if(puzzle[randomRowTemp][randomCol]==0)
                          {
                              randomRowTemp--;
                          }
                          else
                          j=puzzleWords.get(i).length()+1;
                        }
                  }
                  if(j==puzzleWords.get(i).length())
                  {
                      for(k=0;k<puzzleWords.get(i).length();)
                      {
                          puzzle[randomRow][randomCol]=puzzleWords.get(i).charAt(k);
                          randomRow--;
                          k++;
                      }
                      i++;
                  }
              }
           }
           for(int l=0;i<gridDimension;i++)
           {
               for(int m=0;j<gridDimension;j++)
               {
                   if(puzzle[l][m]==0)
                   {
                       int randomAlphabeticChar = (int)(Math.random()*alphabet.length);
                       puzzle[l][m]=alphabet[randomAlphabeticChar];
                   }
               }
           }
        }
    }

    when I try to run an instance of the program(using BlueJ) I get an error saying there is a null pointer exception at line 35 which is
    wordsForGrid.add(puzzleWords.get(pos));
    I am thinking that this is related to the fact that at this line in the loadWordsFromFile method
    List <String>words=new ArrayList<String>();
    I could not create an empty list of string type, i.e List<String>words = new List<String>();

    Is this correct? Or am I looking in the wrong place. The textfile I am using contains over 6000 words on a separate line for each if that makes any difference. I would appreciate any help or guidance with this.
    Thanks


  2. #2
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    Default Re: Problem with lists

    This statement declares the variable wordsForGrid:

    private List<String> wordsForGrid; // line 11

    but it doesn't initialize it, as in:

    wordsForGrid = new ArrayList<String>(); // due to type inference, 'String' is optional in Java 7 and above

    The uninitialized variable is therefore 'null'. The initialization would normally occur in the constructor.

  3. #3
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    Default Re: Problem with lists

    Thanks for the quick reply, seems to have solved the problem for me.

  4. #4
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    Default Re: Problem with lists

    You're welcome. Glad to help.

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