Thread: need help constructing get method

This is one of three trees I am using to parse text and print out every unique word, the line numbers it appears on, and the number of times it appears. I have already used a hash and tree map and have both of them working correctly. My instructor said that we need to use an AVL tree for the third map and gave us code. This is where I am unsure where to go. I will include the method that creates/fills the AVL map as well as the AVL map class. If further code is needed, I will gladly include it.

AvlMap class

//AvlMap class. implements map and extends Comparable
@SuppressWarnings("rawtypes")
public class AvlMap <AnyType extends Comparable<? super AnyType>> implements Map 
{
	    //construct the tree
	    public AvlMap( ){
	        root = null;
	    }
 
	    //inserts object into the map
	    public void insert( AnyType x, AnyType y ){
	        root = insert( x, y, root );
	    }
 
	    //removes the key from the map
	    public void remove( AnyType x ){
	        root = remove( x, root );
	    }
 
	    //internal method to remove from a subtree
	    private AvlNode<AnyType> remove( AnyType x, AvlNode<AnyType> t ){
	        if( t == null )
	            return t;   // Item not found; do nothing
 
	        int compareResult = x.compareTo( t.key );
 
	        if( compareResult < 0 )
	            t.left = remove( x, t.left );
	        else if( compareResult > 0 )
	            t.right = remove( x, t.right );
	        else if( t.left != null && t.right != null ) // Two children
	        {
	            t.key = findMin( t.right ).key;
	            t.right = remove( t.key, t.right );
	        }
	        else
	            t = ( t.left != null ) ? t.left : t.right;
	        return balance( t );
	    }
.
.
.
		@Override
		public Object get(Object key) {
		//method in question	
		}

WordStats class

import java.util.SortedSet;
import java.util.TreeSet;
 
//WordStats class
public class WordStats {
 
	//local variable occurrences and creates new set with lineNumbers
	private int occurrences;
	private SortedSet<Integer> lineNumbers = new TreeSet<Integer>();
 
	//adds line number to the set
	public void addOccurrence(int lineNumber){
		occurrences++;
		lineNumbers.add(lineNumber);
	}
 
	//returns the occurrences variable
	public int getOccurrences(){
		return occurrences;
	}
 
	//returns the line numbers stored in the set
	public SortedSet<Integer> getLines(){
		return lineNumbers;
	}
}

This is the method specifically called to run everything for the AVL Map

public void avlMap(String fileName){
 
		//try/catch block to check for invalid file name
		try{
			//creates new bufferedreader object for input file
			BufferedReader inFile = new BufferedReader(new FileReader(fileName));
 
			//creates new treeMap object named avlMap
			Map avlMap = new AvlMap();
			String oneLine;
 
			//Read the words and add them to the avlMap
			for (int lineNum = 1; (oneLine = inFile.readLine()) != null; lineNum++){
				String delims = " !@#$%{}[]/^&*,.()-;:\'\"\t";
				StringTokenizer st = new StringTokenizer(oneLine, delims);
				while (st.hasMoreTokens()){
					String word = st.nextToken();
					//vvvvvvvvvvvvvvv this is the line that is causing problems-----------------------------------------------
                                        WordStats stats = (WordStats)avlMap.(word);
 
					//if WordStats is empty/doesnt exist,
					//if exists, adds line numbers into a WordStats in the value
					//...field for the int's respective key
					if (stats == null){
						stats = new WordStats();
						avlMap.put(word, stats);
					}
					//WordStats already exists for the word
					//calls addOccurrence method and adds the line number
					stats.addOccurrence(new Integer(lineNum));	
				}
			}
 
			//creates a new iterator object to iterate entries
			Iterator itr = avlMap.entrySet().iterator();
 
			//runs printEntry for each key in the treeMap
			while (itr.hasNext()){
				printEntry((Map.Entry)itr.next());
			}
		}
			//the file name used wasn't able to be reached
			catch(IOException e){
				e.printStackTrace();
			}
	}

I commented the line causing problems. I need to see if the wordstats already exists and return it, or return null if it doesnt.

Originally Posted by Norm

Can you explain what the problems are?

I need the get method to receive a string value, check if it exists in the tree, and return either the object/key that the string corresponds to or a null value if it does not exist. I know I need to change the parameter to (String inputString), but the code inside the method is what I need help with.

yes, to see if it exists. if it doesn't, return null.