Lab 13: GUI Part I

The goal of this lab is to practice using Java's GUI capabilities to write programs that use windows and buttons.

As usual, make a new directory for this project and cd into it.

1. Introduction

A Fifteen Puzzle (or, more generally, an N-puzzle) consists in a grid of square, same-sized tiles, with all but one grid positions filled. The object of the game is to rearrange the tiles by sliding the tiles one at a time until a certain configuration is reached (for example, starting from a random configuration until the numbers are in order).

In this lab, you will write a program that simulates a Fifteen Puzzle

2. Set-up

Copy the following files from the class public directory:

/homeemp/tvandrun/pub/235/gui/FifteenPuzzle.java
/homeemp/tvandrun/pub/235/gui/PuzzlePiece.java

Open FifteenPuzzle.java in xemacs and read through it. Notice that it basically adds sixteen buttons to the window. Compile and run, and notice that the buttons are put right on top of each other, and all the buttons are blank.

3. Adjusting the window

Based on what we saw in class yesterday, play around with the size, location, and layout management until it looks reasonably nice. Don't bother putting text on the buttons yet.

4. Making the puzzle work

Each button stands for a tile or block in the puzzle. 15 of them will have numbers, and the 16th will be blank. We won't actually move the buttons around; instead, we will change the numbers on the buttons to give the appearance of moving tiles.

When a button is clicked, the following should happen:

• If it is blank, nothing should happen.
• Similarly, if it is not blank and none of its neighbors are blank (neighbors meaning immediately above, below, left, or right; diagonals do not count), nothing should happen.
• If one of its neighbors is the blank one, then the blank neighbor should change to have the clicked button's number, and the clicked button should turn blank.

Each button needs to have an action listener to perform this. Uncomment the relevant sections in FifteenPuzzle.java. We are using an action listener class called PuzzlePiece. The skeleton of this class is given to you. Finish it by filling in the bodies for the following methods (read through all this before starting, though):

• PuzzlePiece(JButton, int). This is the constructor, and it tells the action listener what button it is attached to and the number in the order the buttons where made (1 to 16). In addition to initializing the instance variables, this constructor should also set the button's text (hint: you might as well start it out with the int the constructor receives, except that the 16th button should be blank).
• addNeighbor(PuzzlePiece). When a button is clicked, it affects its neighbors. The action listener is not going to have direct access to the neighboring buttons, but it should have references to the action listeners attached to those buttons. Think about: We will need to have access to these neighbors later when writing actionPerformed(). How can we store this information for later reuse? Hint: Notice that not all PuzzlePieces have the same number of neighbors.
• actionPerformed(ActionEvent). This method should implement the algorithm described above.

Hint: Notice again that when a button is clicked, its action listener must communicate with the action listeners on the neighboring buttons---first, to determine if one of the neighbors is blank; second, to make any necessary changes. How can you do this? You may want to write a few extra methods in the class PuzzlePiece.

5. Turn in

Mail the files you modified to Joe.