Lecture Java methods: Object-oriented programming and data structures (2nd AP edition): Chapter 18 - Maria Litvin, Gary Litvin

Chapter 18 - Mouse, keyboard, sounds, and images. This is essentially a “learning by doing” chapter. Not much theory here. This chapter also introduces bit-wise logical operators in the context of identifying the status of keyboard modifier keys (Alt, Shift, Ctrl).

Mouse, Keyboard, Sounds,

and Data Structures

Maria Litvin ● Gary Litvin 2nd AP edition with GridWorld

Chapter

• Learn the basics of playing sounds and

displaying images in applets and

applications

addMouseListener(this);

addMouseMotionListener(this); // optional

Mouse Events (cont’d)

• The MouseListener interface defines five

methods:

void mousePressed (MouseEvent e)

void mouseReleased (MouseEvent e)

void mouseClicked (MouseEvent e)

void mouseEntered (MouseEvent e)

void mouseExited (MouseEvent e)

• One click and release causes several calls Using only mouseReleased is usually a safe bet

Called when the mouse cursor

enters/exits component’s visible area

Mouse Events (cont’d)

• Mouse listener methods receive a

MouseEvent object as a parameter

• A mouse event can provide the coordinates of the event and other information:

public void mousePressed (MouseEvent e)

Mouse Events (cont’d)

• The MouseMotionListener interface adds two methods:

void mouseMoved (MouseEvent e)

void mouseDragged (MouseEvent e)

• These methods are often used together with

MouseListener methods (the same class

implements both interfaces)

Called when the mouse has moved with a button held down

requestFocus method.

• A component (for example, a JPanel) can

serve as its own key listener:

addKeyListener(this);

Keyboard Events (cont’d)

• The KeyListener interface defines three methods:

void keyPressed (KeyEvent e)

void keyReleased (KeyEvent e)

void keyTyped (KeyEvent e)

• One key pressed and released causes several events

Keyboard Events (cont’d)

• Use keyTyped to capture character keys (that

is, keys that correspond to printable

}

Keyboard Events (cont’d)

• Use keyPressed or keyReleased to handle

“action” keys, such as cursor keys, <Enter>, function keys, and so on

• e.getKeyCode() returns and int, the key’s

“virtual code.”

• The KeyEvent class defines constants for various virtual keys For example:

VK_LEFT, VK_RIGHT, VK_UP, VK_DOWN

VK_HOME, VK_END, VK_PAGE_UP, etc.

Cursor keys

Home, etc.

Keyboard Events (cont’d)

• e.isShiftDown(), e.isControlDown(),

e.isAltDown() return the status of the

respective modifier keys

• e.getModifiers() returns a bit pattern that represents the status of all modifier keys

• KeyEvent defines “mask” constants

CTRL_MASK, ALT_MASK, SHIFT_MASK, and so on

Playing Audio Clips

• The JApplet class has a method getAudioClip

that returns an AudioClip object

tune.play(); There may be a slight

delay The audio clip is actually loaded only when

you call its play method

for the first time.

Playing Audio Clips (cont’d)

• URLPath is the path part of the URL where the audio clip file is located

getDocumentBase() is often used for this parameter

• getDocumentBase() returns the path part of the absolute URL of this applet’s HTML file:

AudioClip bells = getAudioClip ( getDocumentBase(), “sounds/Bells.wav");

Images

• The JApplet class has a method getImage

that returns an Image object

Images (cont’d)

• In applications, it may be easier to work with

Swing’s ImageIcon objects:

(usually this)

The Drawing Editor Program

Drawing Editor (cont’d)

• Allows to move and shape objects on

“canvas” using the mouse and the cursor keys

• Here the shapes are circles (“balloons”)

• Uses JColorChooser to pick a color

Drawing Editor (cont’d)

is a detailed step-by-step plan in

the book (Section 18.4).

ControlPanel

DrawingPanel

Balloon BalloonDraw

Review:

• Name the five methods of the MouseListener

interface

• Can a class implement MouseMotionListener

but not MouseListener?

• What are the units and the origin for the

coordinates returned by the MouseEvent’s

getX and getY methods?

• How many methods does the KeyListener

interface specify?

Review (cont’d):

• Which KeyListener’s method is used to

capture an action key event?

• Which KeyEvent’s method returns the actual character typed?

• Which KeyEvent’s methods return the status

of modifier keys?

• When do we need a requestFocus() call?