Keeps finding a "Object" not the real type.. I am really lost.. :D

Question

The calls to other objects work fine, I have testing all of them.. but! when I compile I get a error about finding a "object" type and not a String type at
for(String blackStone : blackUnits.keySet())
               if( getSetLib(blackStone) == 0 ) { removeSet.add(blackStone); }
         }   this is the whole class
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Set;
public class Stat
    private Token[][] board;
    private int bSize;
    private HashMap<String, HashSet> unitsWhite;
    private HashMap<String, HashSet> unitsBlack;
    double last;
    public Stat(Token[][] goBoard, int size)
        board = goBoard;
        bSize = size;
        unitsWhite = new HashMap< String , HashSet>();
        unitsBlack = new HashMap< String , HashSet>();
        last = bSize -1;
     * Delimiter is /
    public HashSet getLib(int x , int y)
        HashSet liberties = new HashSet<String>();
        //error catch
        if(board[x][y] == null){return liberties;}
        int tempX = x;
        int tempY = y;
        //error catch for out of rage if size ect..
        for(int i = 0 , liby = y ,libx = x ; i <= 3; i++)
            if(i == 0){libx = -1; liby = 0;}
            if(i == 1){libx = 0; liby = -1;}
            if(i == 2){libx = 1; liby = 0;}
            if(i == 3){libx = 0; liby = 1;}
            tempX = x+libx;
            tempY = y+liby;
            if(tempX >= 0 || tempY >= 0)
                if( tempX <= last || tempY <= last )   
                     if( (tempX < 0 || tempY < 0) || ( tempX >= last || tempY >= last ) )
                       tempX = 0;
                       tempY = 0;
                     else
                        if( board[tempX][tempY] == null) { liberties.add(tempX+"/"+tempY); }
        return liberties;  
    public void getTer()
    public void checkForCaptured()
        Token black = null;
        Token white = null;
        HashMap blackUnits;
        HashMap whiteUnits; 
        HashSet removeSet ;
        removeSet = new HashSet<String>();
        //look for a Token on the board and if you find one look for any dead  Tokens
        //looks for a Token
        for(int x=0; x < bSize;x++)
          { for(int y=0 ; y < bSize   ;y++)
           { if(board[x][y] != null)
               if (black == null)if( board[x][y].getColor().equals("black") ) black =  board[y][x];
               if (white == null)if( board[x][y].getColor().equals("white") ) white =  board[y][x];
        System.out.println("this is black tokens color" +black.getColor());
        //looks for a dead unit
        if(black != null)
         { blackUnits = black.getUnits();
           System.out.println("black :" +blackUnits.keySet().size() ) ;
           for(String blackStone : blackUnits.keySet())
               if( getSetLib(blackStone) == 0 ) { removeSet.add(blackStone); }
        if(white != null)
        { whiteUnits = white.getUnits();
            System.out.println(" white: "+whiteUnits.keySet().size() );
          for( String whiteStone : whiteUnits.keySet() )
           { if( getSetLib(whiteStone) == 0 ) { removeSet.add(whiteStone); } }
        board.removeUnitsSet(removeSet);    
     public int getSetLib(HashSet Units)
         return 0;
}someone point me in the correct direction PLZ! I don't mind RTFM if you give me a FM and page/line to look at.
THANKS!
Message was edited by:
monji112000

Answer 1

The compiler doesn't know that you're only putting Strings in as keys. HashMap takes references to Object as keys and hence returns references to Object in keySet(). Note, however, that the object itself is still what you put in there. But the compiler only has the declared return type of the method to look at.
// pre 1.5
for (Iterator iter = set.iterator(); iter.hasNext();) {
    String key = (String)iter.next(); // cast Object to String. Only works if you actually put a String in
    // do stuff with key
// 1.5, if you don't use generics
for (Object obj : set) {
    String key = (String)obj;
    // do stuff with key
// 1.5, with generics
Set<String> set = ...;
for (String key : set) {
    // do stuff with key
}Since you have a Map, you'll have Map<String, SomeValueType>.
http://java.sun.com/j2se/1.5.0/docs/guide/language/generics.html
http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf