Step 2: The Board class

To focus on learning Java, you may reasonably ignore the Tetrominos class. It will be the file that you run to start the program, but the Board class can be thought of as the core of your Tetrominos program, and it’s where you’ll write the most code. Go to Eclipse and start reading the code now.

The keyword extends and some provided code in the constructor set the Board up as a user interface component that can be added to a window, and you may safely ignore this code.

Each of the other existing methods in the Board class will be called in response to certain actions, either by the user, or due to time passing. Specifically:

• paintComponent will be called any time you need to draw the blocks on the screen.

• nextTurn will be called every 300 milliseconds, when it is time to move the active piece downwards on the screen.

• slide, rotateLeft, and rotateRight will be called when the user presses control keys to move the game piece. Calls to repaint() in these methods request that paintComponent be called so that you can see the results of the action.

Exercise: test user actions

Add System.out.println calls to nextTurn, slide, rotateLeft, and rotateRight, and run the program. Observe how methods are called in response to the timer and in response to key presses

Drawing to the screen with Graphics objects

Swing drawing is done using objects of the JComponent class. The extends keyword in the definition of Board indicates that a Board can be used as a JComponent, and has several standard methods available to it. Once a JComponent has been added to the user interface (in this case by Tetrominos.java), the special method paintComponent will be called whenever the user interface needs to draw that component.

So, if you put drawing code in paintComponent of the Board class, that drawing code will be called at least once, when the main window is initially drawn. When paintComponent is drawn, it is passed a parameter, a reference to a Graphics object. You can draw on the component using methods of this Graphics object.

The starter code I’ve provided draws two rectangles: