Class ShapeCanvas

java.lang.Object
  |
  +--java.awt.Component
        |
        +--java.awt.Canvas
              |
              +--ShapeCanvas

class ShapeCanvas

extends java.awt.Canvas

implements java.awt.event.ActionListener, java.awt.event.ItemListener, java.awt.event.MouseListener, java.awt.event.MouseMotionListener

ShapeCanvas class This class represents a canvas that can display colored shapes and let the user drag them around. It uses an off-screen images to make the dragging look as smooth as possible.

Since:

11/10/2000

 Update History
 --------------
 Date		By		Description
 ----		--		-----------
 11/10/00	Asha Mony	Creation

See Also:

Serialized Form

Inner classes inherited from class java.awt.Component

java.awt.Component.AWTTreeLock

Field Summary

(package private) java.awt.Color	currentColor
(package private) java.awt.Image	offScreenCanvas
(package private) java.awt.Graphics	offScreenGraphics
(package private) int	prevDragX
(package private) int	prevDragY
(package private) Shape	shapeBeingDragged
(package private) java.util.Vector	shapes

Fields inherited from class java.awt.Canvas

base, graphicsConfig, nameCounter, serialVersionUID

Fields inherited from class java.awt.Component

actionListenerK, adjustmentListenerK, appContext, assert, background, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, changeSupport, componentListener, componentListenerK, componentOrientation, componentSerializedDataVersion, containerListenerK, cursor, dropTarget, enabled, eventMask, focusListener, focusListenerK, font, foreground, hasFocus, height, incRate, inputMethodListener, inputMethodListenerK, isInc, isPacked, itemListenerK, keyListener, keyListenerK, LEFT_ALIGNMENT, locale, LOCK, minSize, mouseListener, mouseListenerK, mouseMotionListener, mouseMotionListenerK, name, nameExplicitlySet, newEventsOnly, ownedWindowK, parent, peer, peerFont, popups, prefSize, RIGHT_ALIGNMENT, serialVersionUID, textListenerK, TOP_ALIGNMENT, valid, visible, width, windowListenerK, x, y

Constructor Summary

(package private)

ShapeCanvas()

Method Summary

void	actionPerformed(java.awt.event.ActionEvent evt) Called to respond to action events.
(package private) void	addShape(Shape shape)
void	itemStateChanged(java.awt.event.ItemEvent evt) This is called to respond to item events.
(package private) void	makeOffScreenCanvas()
void	mouseClicked(java.awt.event.MouseEvent evt)
void	mouseDragged(java.awt.event.MouseEvent evt) User has moved the mouse.
void	mouseEntered(java.awt.event.MouseEvent evt)
void	mouseExited(java.awt.event.MouseEvent evt)
void	mouseMoved(java.awt.event.MouseEvent evt)
void	mousePressed(java.awt.event.MouseEvent evt) User has pressed the mouse.
void	mouseReleased(java.awt.event.MouseEvent evt) User has released the mouse.
void	paint(java.awt.Graphics g) In the paint method, everything is drawn to an off-screen canvas, and then that canvas is copied onto the screen.
void	update(java.awt.Graphics g) Update method is called when canvas is to be redrawn.

Methods inherited from class java.awt.Canvas

, addNotify, constructComponentName, postsOldMouseEvents

Methods inherited from class java.awt.Component

action, add, addComponentListener, addFocusListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addPropertyChangeListener, addPropertyChangeListener, areInputMethodsEnabled, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, deliverEvent, disable, disableEvents, dispatchEvent, dispatchEventImpl, doLayout, enable, enable, enableEvents, enableInputMethods, eventEnabled, firePropertyChange, getAlignmentX, getAlignmentY, getBackground, getBounds, getBounds, getColorModel, getComponentAt, getComponentAt, getComponentOrientation, getCursor, getDropTarget, getFont_NoClientCode, getFont, getFontMetrics, getForeground, getGraphics, getHeight, getInputContext, getInputMethodRequests, getIntrinsicCursor, getLocale, getLocation, getLocation, getLocationOnScreen, getMaximumSize, getMinimumSize, getName, getNativeContainer, getParent_NoClientCode, getParent, getPeer, getPreferredSize, getSize, getSize, getToolkit, getToolkitImpl, getTreeLock, getWidth, getWindowForObject, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, initIDs, inside, invalidate, isDisplayable, isDoubleBuffered, isEnabled, isEnabledImpl, isFocusTraversable, isLightweight, isOpaque, isShowing, isValid, isVisible, keyDown, keyUp, layout, lightweightPrint, list, list, list, list, list, locate, location, lostFocus, minimumSize, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, paramString, postEvent, preferredSize, prepareImage, prepareImage, print, printAll, printHeavyweightComponents, processComponentEvent, processEvent, processFocusEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, readObject, remove, removeComponentListener, removeFocusListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeNotify, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, reshape, resize, resize, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFont, setForeground, setLocale, setLocation, setLocation, setName, setSize, setSize, setVisible, show, show, size, toString, transferFocus, validate, writeObject

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, registerNatives, wait, wait, wait

Field Detail

offScreenCanvas

java.awt.Image offScreenCanvas

offScreenGraphics

java.awt.Graphics offScreenGraphics

shapes

java.util.Vector shapes

currentColor

java.awt.Color currentColor

shapeBeingDragged

Shape shapeBeingDragged

prevDragX

int prevDragX

prevDragY

int prevDragY

Constructor Detail

ShapeCanvas

ShapeCanvas()

Method Detail

paint

public void paint(java.awt.Graphics g)

In the paint method, everything is drawn to an off-screen canvas, and then that canvas is copied onto the screen.

Overrides:

paint in class java.awt.Canvas

Since:

11/10/2000

 Update History
 --------------
 Date		By		Description
 ----		--		-----------
 11/10/00	Asha Mony	Creation

update

public void update(java.awt.Graphics g)

Update method is called when canvas is to be redrawn. Just call the paint method.

Overrides:

update in class java.awt.Component

Since:

11/10/2000

 Update History
 --------------
 Date		By		Description
 ----		--		-----------
 11/10/00	Asha Mony	Creation

makeOffScreenCanvas

void makeOffScreenCanvas()

itemStateChanged

public void itemStateChanged(java.awt.event.ItemEvent evt)

This is called to respond to item events. Such events can only be sent by the color choice menu, so respond by setting the current color according to the selected item in that menu.

Specified by:

itemStateChanged in interface java.awt.event.ItemListener

Since:

11/10/2000

 Update History
 --------------
 Date		By		Description
 ----		--		-----------
 11/10/00	Asha Mony	Creation

actionPerformed

public void actionPerformed(java.awt.event.ActionEvent evt)

Called to respond to action events. The three shape-adding buttons have been set up to send action events to this canvas. Respond by adding the appropriate shape to the canvas.

Specified by:

actionPerformed in interface java.awt.event.ActionListener

Since:

11/10/2000

 Update History
 --------------
 Date		By		Description
 ----		--		-----------
 11/10/00	Asha Mony	Creation

addShape

void addShape(Shape shape)

mousePressed

public void mousePressed(java.awt.event.MouseEvent evt)

User has pressed the mouse. Find the shape that the user has clicked on, if any. If there is a shape at the position when the mouse was clicked, then start dragging it. If the user was holding down the shift key, then bring the dragged shape to the front, in front of all the other shapes.

Specified by:

mousePressed in interface java.awt.event.MouseListener

Since:

11/10/2000

 Update History
 --------------
 Date		By		Description
 ----		--		-----------
 11/10/00	Asha Mony	Creation

mouseDragged

public void mouseDragged(java.awt.event.MouseEvent evt)

User has moved the mouse. Move the dragged shape by the same amount.

Specified by:

mouseDragged in interface java.awt.event.MouseMotionListener

Since:

11/10/2000

 Update History
 --------------
 Date		By		Description
 ----		--		-----------
 11/10/00	Asha Mony	Creation

mouseReleased

public void mouseReleased(java.awt.event.MouseEvent evt)

User has released the mouse. Move the dragged shape, then set shapeBeingDragged to null to indicate that dragging is over. if the shape lies completely outside the canvas, remove it from the list of shapes (since there is no way to ever move it back onscreen).

Specified by:

mouseReleased in interface java.awt.event.MouseListener

Since:

11/10/2000

 Update History
 --------------
 Date		By		Description
 ----		--		-----------
 11/10/00	Asha Mony	Creation

mouseEntered

public void mouseEntered(java.awt.event.MouseEvent evt)

Specified by:

mouseEntered in interface java.awt.event.MouseListener

mouseExited

public void mouseExited(java.awt.event.MouseEvent evt)

Specified by:

mouseExited in interface java.awt.event.MouseListener

mouseMoved

public void mouseMoved(java.awt.event.MouseEvent evt)

Specified by:

mouseMoved in interface java.awt.event.MouseMotionListener

mouseClicked

public void mouseClicked(java.awt.event.MouseEvent evt)

Specified by:

mouseClicked in interface java.awt.event.MouseListener