Questions about PuzzleModel, PuzzleView/Gui, PuzzleController

The following method is part of PuzzleGui, this method is called as part of the initialization of that class. Explain the purpose of the method (do a best guess based on the names of the parameters and variables).


    private void constrainResize()
    {
	addComponentListener(new ComponentAdapter(){
		public void componentResized(ComponentEvent e)
		{
		    int w = getWidth();
		    int h = getHeight();
		    w = Math.max(w,h);
		    setSize(w,w);
		}
	    });
	
    }

In the PuzzleGui class the private instance variable myUndo is of type JMenuItem. Here's the code that initializes this variable. In broad terms, explain each major part of this initialization.

	myUndo = new JMenuItem(new AbstractAction("Undo")
	    {
		public void actionPerformed(ActionEvent e) {
		    myControl.undoMove();
		}
	    });
	setEnabledUndo(false);
	menu.add(myUndo);

The code below creates moveMaker, an object which is attached to each of the n² JButtons in a PuzzleGui view that's the view of an n x n puzzle. Why is it possible to share the same object among all the buttons, e.g., rather than using a different button-specific listener for each button? (explain what happens when a button is pressed based on the code below).
```
	    
  ActionListener moveMaker = new ActionListener(){
         public void actionPerformed(ActionEvent e)
         {
	    int val = Integer.parseInt(e.getActionCommand());
            myControl.makeMove(new PuzzleMove(val));
         }
  };
```

The code below from PuzzleModel makes a move in the model. Explain based on best-guess information (based on the names of the methods and variables) the purpose of the statements in the scope of the if statement that calls isNeighbors. Note: the instance field myList stores all moves for the purpose of undo.


    private boolean doMove(PuzzleMove move, boolean doStore)
    {
	int index = getIndex(move.getValue());
	int blankIndex = getIndex(getBlankValue());
	
	if (isNeighbors(index,blankIndex)) {
	    int temp = myNumbers[blankIndex];
	    myNumbers[blankIndex] = myNumbers[index];
	    myNumbers[index] = temp;

	    myControl.showBoard(myNumbers);
	    if (doStore){
		myList.add(move);
	    }
	    return true;
	}
	return false;	
    }

The code below is from PuzzleModel. Explain each line of this function. The instance variable myList is of type java.util.LinkedList rather than ArrayList because the latter field doesn't have a method removeLast.

    /**
     * Undoes the last move (if there is one) and returns true iff
     * another undo is possible
     * @return true if another undo is possible, else returns false
     */
    public boolean undo()
    {
	if (myList.size() != 0) {
	    doMove((PuzzleMove) myList.removeLast(),false);
	}
	return myList.size() > 0;
    }

IconCounterCounter Questions

The IconCounterCounter class static method getCount returns the number of times it's called with a specific parameter, e.g., it returns 1 the first time called with a parameter whose value is the image for "blarg.jpg", 2 the second time called with the same parameter, etc. The prototype is:
```
    public static int getCount(Image im)
```
Internally, the IconCounterCounter class uses a HashMap to store an image and its associated count of how many times getCount has been called.
If a TreeMap is used instead of a HashMap internally, the code will compile fine. However, when the PuzzleApp program is run, the following class-cast exception is generated. Explain this.
```
Exception in thread "main" java.lang.ClassCastException: sun.awt.windows.WImage
        at java.util.TreeMap.compare(TreeMap.java:1081)
        at java.util.TreeMap.getEntry(TreeMap.java:341)
        at java.util.TreeMap.get(TreeMap.java:260)
        at IconCounterCounter.getCount(IconCounterCounter.java:31)
```