# CS2133: Computer Science II Assignment 3 solution

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1 Message in a Bottle (20 points)
Create a MessageFrame class extending JFrame and a MessagePanel class extending JPanel. Add the panel to the frame’s contentPane. The frame should be titled “Message in a Bottle” and should end the program when the close box is clicked. In the panel, draw a bottle shape using some combination of Graphics object methods like drawLine, drawPolygon, drawPolyline, drawRoundRect and drawArc (look up the Graphics object in the Java API for details). Make the bottle as attractive as you can, although you won’t be graded on artistic merit. In the center of the bottle shape, add a message string. Create a Message class with a main method that instantiates the MessageFrame and gets the ball rolling.
2 Sierpinski’s Triangle (30 points)
Sierpinski’s Triangle is a simple and famous example of a fractal image. It is built recursively from a simple set of rules, illustrated in Figure 2. Your task will be to create an application that illustrates a perfect Sierpinski triangle, regardless of how large the application frame is. As the user moves and resizes the application window, the triangle should be redrawn and made larger or smaller as appropriate. Your program should display a frame that is based on the size of the user’s screen. The paintComponent method of the panel on which you are drawing will be called whenever the frame is resized, so that happens automagically and you don’t have to worry about it. JPanels include a getHeight() and getWidth() method that you will be able to use to get the information you need for passing to a recursive draw function that you will write. The draw algorithm takes the coordinates of a square area of the screen as input. If that square is the size of a single pixel, it should call drawRect() on the Graphics object passed into paintComponent, drawing a one-pixel square somewhere on the screen. If larger, it should call the draw method three times recursively, once on the lower left quadrant of the square, once on the lower right, and once on an area centered above the other two (as illustrated in Figure 2). The solution will look a lot like Figure 3, with the largest triangle ﬁtting into the largest square area of the frame, and the smallest triangles being three pixels in size.
3 Minesweeper (50 points)
You are going to write the game of Minesweeper. The Minesweeper board is a graphical grid of squares. A certain number of squares, chosen randomly, conceal dangerous mines. Play proceeds
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Figure 1: Example output for Problem 1. Feel free to be more creative than this.
Figure 2: Fractal representation of Sierpinski construction from Problem 2. (Image source: Wikipedia)
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Figure 3: Representative illustration of the Sierpinski problem solution.
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Figure 4: A half-completed game of Minesweeper with a rudimentary design.
when a user clicks on a square. If that square hides a mine, the game is over and the player loses. If not, then stepping on the square reveals the number of mines hidden by squares adjacent to that square – a number between 0 and 8. A player can right-click on a square to mark it as being potentially mined, and remove the mark with another right-click. Figure 4 shows a game in progress. Numbers represent squares that have been clicked, ’F’s are places the player has placed a ﬂag, and ’?’s are squares that have not yet been clicked. This is a singularly unattractive gameboard; you are welcome to add icons or grid squares or any other kinds of graphics to liven up your own version. You are responsible for designing and implementing the whole game. This is a big task; start early. Here are some suggestions.
• Model-View-Controller architecture! Implement a minesweeper class that plays the game without relying on any GUI elements, instead using method calls for making moves and sending information. This is the model. The paintComponent methods of your UI objects should ask this model what to display. This is the view. The event handlers should call the
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gameplay methods in the model. This is the controller. Don’t let things get mixed up or complicated! • This is a perfect setting for using a GridLayout. Make it easy to change the number of squares on the board, maybe by setting a static ﬁnal int. • JButtons seem at ﬁrst like a good choice for board squares, but they do not know how to respond to right-clicks. You will want to use a MouseAdapter attached to your panel rather than an ActionListener attached to buttons. A grid full of JLabels that have been extended to have access to the model, and to know where they sit in the grid, would work, as would other more attractive user interface elements. • When you are setting up your board, you need to randomly determine whether each square is mined or safe. You can select a speciﬁc number of squares to be mines, or you can assign each square’s status based on a certain probability of being a mine. The latter is easier. • You will need to do something useful with the physical X- and Y-pixels that your MouseEvents report. Within a JPanel, the method getComponentAt(int x, int y) will return the GUI component located at that pixel. This is a good way to retrieve the objects you’ve added to the grid. You can then query them to ﬁnd out whether they’re mined or safe, and change their display properties (such as from blank to ﬂagged to numbered). • The class with the main method (Minesweeper.java) and the one extending your JFrame should be only be a couple of lines. All of the heavy lifting will probably take place in the class that extends JPanel. Your MouseListener can be an inner class there, too. • Make sure the program ends in a satisfying manner when the user clicks on a bomb. Extra Credit: Because it is always safe to click every mine surrounding a square with a ’0’ in it, most commercial versions of the game will automatically do so, and then do it again for any new ’0’ squares uncovered. This can reveal large swaths of safe territory with a single click. Implement this functionality. Extra Credit: In the header area of the JFrame’s BorderLayout, implement a counter showing how many mines remain to be found. This should initially report the number of mines on the board, and decrement or increment whenever the player plants or removes a ﬂag. Extra Credit: Wow us with the graphic design of your game.
Turning in
This is the ﬁrst assignment where the design of the programs, and thus the Java ﬁles you will require, have been left up to you. The ﬁles with the main() function that actually execute the programs, however, should be named Message.java, Sierpinski.java and Minesweeper.java, so we know which ones we’re supposed to run. Those three, plus all of the other .java ﬁles that deﬁne the classes you need for these programs – your subclassed JFrames and JPanels and the like – should be wrapped up in a zip ﬁle called assignment 3