LESSON NOTE/GUIDE
|
THE
CODE public void setup() { size(400,
300); surface.setTitle("Press A"); } public void draw() {} public void keyPressed() { if ((key == 'a') ||
(key == 'A')) { System.out.println("The letter A was
pressed."); } } |
RESULT A window appears.
As long as the focus is on the window, when you press the A key, the
message appears in the console. |
EXPLANATION The method keyPressed() is
automatically executed on frames when a key has been pressed. This is very easy to do! |
PROGRAM
2 – ARROW KEYS
· This program displays a message in the console when
any of the arrow keys are pressed.
Note that the arrow keys are not part of the standard ascii table and are therefore called coded keys. This leads to a slightly different
condition for them. See below.
THE
CODE public void setup() { size(600,
500); surface.setTitle("Use Arrow Keys (when mouse
is over window)"); } public void draw() {} public void keyPressed() { if ((key == CODED)
&& (keyCode == UP)) { System.out.println("UP key pressed"); } if ((key == CODED)
&& (keyCode == DOWN)) { System.out.println("DOWN key pressed"); } if ((key == CODED)
&& (keyCode == LEFT)) { System.out.println("LEFT key pressed"); } if ((key == CODED)
&& (keyCode == RIGHT)) { System.out.println("RIGHT key pressed"); } } |
RESULT A window appears. As
long is the mouse is over the window (giving it focus), whenver you hit an
arrow key, a corresponding message appears in the console. |
EXPLANATION This code is pretty straight
forward. Ask your teacher if you
need help. |
PROGRAM
3 – MOVING OBJECT WITH ARROW KEYS
· This program displays a message in the console when
any of the arrow keys are pressed.
Note that the arrow keys are not part of the standard ascii table and are therefore called coded keys. This leads to a slightly different
condition for them. See below.
THE
CODE public int x; public int y; public void setup() { size(400,
300); surface.setTitle("Use LEFT and RIGHT arrow"); x = width/2; y = height - 10; } public void draw() { background(186); line(x,y,x,y-10); line(x-5,y,x+5,y); } public void keyPressed() { if (key == CODED
&& keyCode == LEFT) { x = x - 2; } else if (key ==
CODED && keyCode == RIGHT) { x = x + 2; } } |
RESULT The upside down T moves left and right with the arrow
keys. |
EXPLANATION At the top, the x and y variables
represent the location of the upside down T. They are data fields so the values are
stored from frame to frame. Inside the setup method, we create
the window. Then, in the last two
lines, we set the upside down T’s x and y initial values. These are conveniently based on the width
and height of the entire window. Inside the draw method, we draw the
background (to erase previous frames) and then we draw the upside down T
again. If it moved, it gets drawn at
a different location, otherwise, it gets drawn at the same location. Inside the keyPressed
method, we move the location of the upside down T whenever the LEFT or RIGHT
arrows are hit. |
Note:
Instead of using keyPressed(), you can also use keyReleased()
that automatically gets executed whenever a keyboard key is released.