liang, introduction to java programming, eighth edition, (c) 2011 pearson education, inc. all rights...

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807 11

Chapter 14 Abstract Classes and Interfaces

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807

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Interfaces

What is an interface?

Why is an interface useful?

How do you define an interface?

How do you use an interface?

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What is an interface? Why is an interface useful?

An interface is a classlike construct that contains only constants and abstract methods. In many ways, an interface is similar to an abstract class, but the intent of an interface is to specify behavior for objects. For example, you can specify that the objects are comparable, edible, cloneable using appropriate interfaces.

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Define an InterfaceTo distinguish an interface from a class, Java uses the following syntax to define an interface:

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public interface InterfaceName { constant declarations; method signatures;}

Example:

public interface Edible {

/** Describe how to eat */

public abstract String howToEat();

}


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Omitting Modifiers in Interfaces

All data fields are public final static and all methods are public abstract in an interface. For this reason, these modifiers can be omitted, as shown below:

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public interface T1 { public static final int K = 1; public abstract void p(); }

Equivalent public interface T1 { int K = 1; void p(); }

A constant defined in an interface can be accessed using syntax InterfaceName.CONSTANT_NAME (e.g., T1.K).


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The ActionListener Interfaces

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HandleEventHandleEvent RunRun


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Handling GUI Events

Source object (e.g., button)

Listener object contains a method for processing the event.

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Interfaces vs. Abstract Classes, cont.

Suppose that c is an instance of Class2. c is also an instance of Object, Class1, Interface1, Interface1_1, Interface1_2, Interface2_1, and Interface2_2.

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Object Class1

Interface1 Interface1_1

Interface1_2

Class2

Interface2_1

Interface2_2

All classes share a single root, the Object class, but there is no single root for interfaces. Like a class, an interface also defines a type. A variable of an interface type can reference any instance of the class that implements the interface. If a class extends an interface, this interface plays the same role as a superclass. You can use an interface as a data type and cast a variable of an interface type to its subclass, and vice versa.


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Wrapper Classes Boolean

Character

Short

Byte

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Integer Long

Float

Double

java.lang.Object

-

Double -

Float -

Long -

Integer -

Short -

Byte -

Character -

Boolean -

Number -

java.lang.Comparable -

NOTE: (1) The wrapper classes do not have no-arg constructors. (2) The instances of all wrapper classes are immutable, i.e., their internal values cannot be changed once the objects are created.


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Conversion MethodsEach numeric wrapper class implements the abstract methods doubleValue, floatValue, intValue, longValue, and shortValue, which are defined in the Number class. These methods “convert” objects into primitive type values.

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The Static valueOf MethodsThe numeric wrapper classes have a useful class method, valueOf(String s). This method creates a new object initialized to the value represented by the specified string. For example:

Double doubleObject = Double.valueOf("12.4");

Integer integerObject = Integer.valueOf("12");

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The Methods for Parsing Strings into Numbers

You have used the parseInt method in the Integer class to parse a numeric string into an int value and the parseDouble method in the Double class to parse a numeric string into a double value. Each numeric wrapper class has two overloaded parsing methods to parse a numeric string into an appropriate numeric value.

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TIP

Java provides a static sort method for sorting an array of Object in the java.util.Arrays class. So you can use the following code to sort arrays in this example:

java.util.Arrays.sort(intArray);

java.util.Arrays.sort(doubleArray);

java.util.Arrays.sort(charArray);

java.util.Arrays.sort(stringArray);

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BigInteger and BigDecimal

If you need to compute with very large integers or high precision floating-point values, you can use the BigInteger and BigDecimal classes in the java.math package. Both are immutable. Both extend the Number class and implement the Comparable interface.

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Chapter 15 Graphics


Java Coordinate System

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(0, 0) X Axis

Y Axis

(x, y)

x

y

Java Coordinate System

X Axis Conventional Coordinate System

(0, 0)

Y Axis


Each GUI Component Has its Own Coordinate System

(0, 0) Component c2

Component c1

(0, 0)

(0, 0) (x1, y1)

(x2, y2)

(x3, y3) Component c3 c3’s coordinate

system

c2’s coordinate system

c1’s coordinate system


The Graphics ClassYou can draw strings, lines, rectangles, ovals, arcs, polygons, and polylines, using the methods in the Graphics class.

java.awt.Graphics

+setColor(color: Color): void

+setFont(font: Font): void

+drawString(s: String, x: int, y: int): void

+drawLine(x1: int, y1: int, x2: int, y2: int): void

+drawRect(x: int, y: int, w: int, h: int): void

+fillRect(x: int, y: int, w: int, h: int): void

+drawRoundRect(x: int, y: int, w: int, h: int, aw: int, ah: int): void

+fillRoundRect(x: int, y: int, w: int, h: int, aw: int, ah: int): void

+draw3DRect(x: int, y: int, w: int, h: int, raised: boolean): void

+fill3DRect(x: int, y: int, w: int, h: int, raised: boolean): void

+drawOval(x: int, y: int, w: int, h: int): void

+fillOval(x: int, y: int, w: int, h: int): void

+drawArc(x: int, y: int, w: int, h: int, startAngle: int, arcAngle: int): void

+fillArc(x: int, y: int, w: int, h: int, startAngle: int, arcAngle: int): void

+drawPolygon(xPoints: int[], yPoints: int[], nPoints: int): void

+fillPolygon(xPoints: int[], yPoints: int[], nPoints: int): void

+drawPolygon(g: Polygon): void

+fillPolygon(g: Polygon): void

+drawPolyline(xPoints: int[], yPoints: int[], nPoints: int): void

Sets a new color for subsequent drawings.

Sets a new font for subsequent drwings.

Draws a string starting at point (x, y).

Draws a line from (x1, y1) to (x2, y2).

Draws a rectangle with specified upper-left corner point at (x, y) and width w and height h.

Draws a filled rectangle with specified upper-left corner point at (x, y) and width w and height h.

Draws a round-cornered rectangle with specified arc width aw and arc height ah.

Draws a filled round-cornered rectangle with specified arc width aw and arc height ah.

Draws a 3-D rectangle raised above the surface or sunk into the surface.

Draws a filled 3-D rectangle raised above the surface or sunk into the surface.

Draws an oval bounded by the rectangle specified by the parameters x, y, w, and h.

Draws a filled oval bounded by the rectangle specified by the parameters x, y, w, and h.

Draws an arc conceived as part of an oval bounded by the rectangle specified by the parameters x, y, w, and h.

Draws a filled arc conceived as part of an oval bounded by the rectangle specified by the parameters x, y, w, and h.

Draws a closed polygon defined by arrays of x and y coordinates. Each pair of (x[i], y[i]) coordinates is a point.

Draws a filled polygon defined by arrays of x and y coordinates. Each pair of (x[i], y[i]) coordinates is a point.

Draws a closed polygon defined by a Polygon object.

Draws a filled polygon defined by a Polygon object.

Draws a polyline defined by arrays of x and y coordinates. Each pair of (x[i], y[i]) coordinates is a point.


paintComponent ExampleIn order to draw things on a component, you need to define a class that extends JPanel and overrides its paintComponent method to specify what to draw. The first program in this chapter can be rewritten using paintComponent.

TestPaintComponentTestPaintComponent RunRun


Drawing Geometric Figures

Drawing Strings Drawing Lines Drawing Rectangles Drawing Ovals Drawing Arcs Drawing Polygons


Drawing Strings

(0, 0) (getWidth(), 0)

(getWidth(), getHeight()) (0, getHeight())

(x, y) s is display here

(0, 0) (getWidth(), 0)

(getWidth(), getHeight()) (0, getHeight())

(x1, y1)

(x2, y2)

drawLine(int x1, int y1, int x2, int y2);drawString(String s, int x, int y);


Drawing Rounded Rectangles

drawRoundRect(int x, int y, int w, int h, int aw, int ah);

fillRoundRect(int x, int y, int w, int h, int aw, int ah);


Drawing OvalsdrawOval(int x, int y, int w, int h);

fillOval(int x, int y, int w, int h);


Case Study: The FigurePanel Class This example develops a useful class for displaying various figures. The class enables the user to set the figure type and specify whether the figure is filled, and displays the figure on a panel.

FigurePanel

+LINE = 1

+RECTANGLE = 2

+ROUND_RECTANGLE = 3

+OVAL = 4

-type: int

-filled: boolean

+FigurePanel()

+FigurePanel(type: int)

+FigurePanel(type: int, filled: boolean)

+getType(): int

+setType(type: int): void

+isFilled(): boolean

+setFilled(filled: boolean): void

javax.swing.JPanel -char token +getToken +setToken +paintComponet +mouseClicked

LINE, RECTANGLE, ROUND_RECTANGLE, and OVAL are constants.

Specifies the figure type (default: 1).

Specifies whether the figure is filled (default: false).

Creates a default figure panel.

Creates a figure panel with the specified type.

Creates a figure panel with the specified type and filled property.

Returns the figure type.

Sets a new figure type.

Checks whether the figure is filled with a color.

Sets a new filled property.

FigurePanelFigurePanel


Test FigurePanelThis example develops a useful class for displaying various figures. The class enables the user to set the figure type and specify whether the figure is filled, and displays the figure on a panel.

TestFigurePanelTestFigurePanel RunRun


Displaying Image IconsYou learned how to create image icons and display image icons in labels and buttons. For example, the following statements create an image icon and display it in a label:

ImageIcon icon = new ImageIcon("image/us.gif");JLabel jlblImage = new JLabel(imageIcon);

An image icon displays a fixed-size image. To display an image in a flexible size, you need to use the java.awt.Image class. An image can be created from an image icon using the getImage() method as follows:

Image image = imageIcon.getImage();


Displaying ImagesUsing a label as an area for displaying images is simple and convenient, but you don't have much control over how the image is displayed. A more flexible way to display images is to use the drawImage method of the Graphics class on a panel. Four versions of the drawImage method are shown here.

java.awt.Graphics +drawImage(image: Image, x: int, y: int,

bgcolor: Color, observer: ImageObserver): void

+drawImage(image: Image, x: int, y: int, observer: ImageObserver): void

+drawImage(image: Image, x: int, y: int, width: int, height: int, observer: ImageObserver): void

+drawImage(image: Image, x: int, y: int, width: int, height: int, bgcolor: Color, observer: ImageObserver): void

Draws the image in a specified location. The image's top-left corner is at (x, y) in the graphics context's coordinate space. Transparent pixels in the image are drawn in the specified color bgcolor. The observer is the object on which the image is displayed. The image is cut off if it is larger than the area it is being drawn on.

Same as the preceding method except that it does not specify a background color.

Draws a scaled version of the image that can fill all of the available space in the specified rectangle.

Same as the preceding method except that it provides a solid background color behind the image being drawn.


Displaying Images ExampleThis example gives the code that displays an image from image/us.gif. The file image/us.gif is under the class directory. The Image from the file is created in the program. The drawImage method displays the image to fill in the whole panel, as shown in the figure.

RunRunDisplayImageDisplayImage


Case Study: ImageViewer ClassDisplaying an image is a common task in Java programming. This case study develops a reusable component named ImageViewer that displays an image in a panel. The ImageViewer class contains the properties image, imageFilename, stretched, xCoordinate, and yCoordinate.

ImageViewer

-image: Image

-stretched: boolean

-xCoordinate: int

-yCoordinate: int

+ImageViewer()

+ImageViewer(imageFile: String)

javax.swing.JPanel

Image in the image viewer.

True if the image is stretched in the viewer.

x-coordinate of the upper-left corner of the image in the viewer.

y-coordinate of the upper-left corner of the image in the viewer.

Constructs an image viewer with no image.

Constructs an image viewer with the specified image file.

The get and set methods for these data fields are provided in the class, but omitted in the UML diagram for brevity.


ImageView ExampleThis example gives an example that creates six images using the ImageViewer class.

RunRunSixFlagsSixFlags


Chapter 16 Event-Driven Programming


Procedural vs. Event-Driven Programming

Procedural programming is executed in procedural order.

In event-driven programming, code is executed upon activation of events.


Revisit Listing 11.7Taste of Event-Driven Programming

The example displays a button in the frame. A message is displayed on the console when a button is clicked.

HandleEventHandleEvent

RunRun


Events

An event can be defined as a type of signal to the program that something has happened.

The event is generated by external user actions such as mouse movements, mouse clicks, and keystrokes, or by the operating system, such as a timer.


Event Classes


Event Information

An event object contains whatever properties are pertinent to the event. You can identify the source object of the event using the getSource() instance method in the EventObject class. The subclasses of EventObject deal with special types of events, such as button actions, window events, component events, mouse movements, and keystrokes. Table 15.1 lists external user actions, source objects, and event types generated.


Selected User ActionsSource Event Type

User Action Object Generated

Click a button JButton ActionEvent

Click a check box JCheckBox ItemEvent, ActionEvent

Click a radio button JRadioButton ItemEvent, ActionEvent

Press return on a text field JTextField ActionEvent

Select a new item JComboBox ItemEvent, ActionEvent

Window opened, closed, etc. Window WindowEvent

Mouse pressed, released, etc. Component MouseEvent

Key released, pressed, etc. Component KeyEvent


The Delegation Model

source: SourceClass

+addXListener(listener: XListener)

listener: ListenerClass

User Action

Trigger an event

XListener +handler(event: XEvent)

Register by invoking source.addXListener(listener);

(a) A generic source component with a generic listener

source: JButton

+addActionListener(listener: ActionListener)

listener: CustomListenerClass

ActionListener

+actionPerformed(event: ActionEvent)

Register by invoking source.addActionListener(listener);

(b) A JButton source component with an ActionListener


Internal Function of a Source Component

source: SourceClass

+addXListener(XListener listener)

(a) Internal function of a generic source object

event: XEvent listener1 listener2 … listenern

+handler(

Keep it a list

Invoke listener1.handler(event) listener2.handler(event) … listenern.handler(event)

An event is triggered

source: JButton

+addActionListener(ActionListener listener)

(b) Internal function of a JButton object

event: ActionEvent

listener1 listener2 … listenern

+handler(

Keep it a list

Invoke listener1.actionPerformed(event) listener2.actionPerformed(event) … listenern.actionPerformed(event)

An event is triggered


The Delegation Model: Example

JButton jbt = new JButton("OK");

ActionListener listener = new OKListener();

jbt.addActionListener(listener);


Selected Event Handlers Event Class Listener Interface Listener Methods (Handlers)ActionEvent ActionListener actionPerformed(ActionEvent)ItemEvent ItemListener itemStateChanged(ItemEvent)WindowEvent WindowListener windowClosing(WindowEvent)

windowOpened(WindowEvent)windowIconified(WindowEvent)windowDeiconified(WindowEvent)windowClosed(WindowEvent)windowActivated(WindowEvent)windowDeactivated(WindowEvent)

ContainerEvent ContainerListener componentAdded(ContainerEvent)componentRemoved(ContainerEvent)

MouseEvent MouseListener mousePressed(MouseEvent)mouseReleased(MouseEvent)

mouseClicked(MouseEvent) mouseExited(MouseEvent) mouseEntered(MouseEvent)KeyEvent KeyListener keyPressed(KeyEvent)

keyReleased(KeyEvent) keyTypeed(KeyEvent)


Example: Second Version for ControlCircle (with listener for Enlarge)

Now let us consider to write a program that uses two buttons to control the size of a circle.

ControlCircle2ControlCircle2 RunRun


Inner Class Listeners

A listener class is designed specifically to create a listener object for a GUI component (e.g., a button). It will not be shared by other applications. So, it is appropriate to define the listener class inside the frame class as an inner class.


Inner Classes

Inner class: A class is a member of another class.

Advantages: In some applications, you can use an inner class to make programs simple.

An inner class can reference the data and methods defined in the outer class in which it nests, so you do not need to pass the reference of the outer class to the constructor of the inner class.

ShowInnerClassShowInnerClass


Inner Classes, cont. public class Test { ... } public class A { ... }

public class Test { ... // Inner class public class A { ... } }

(a)

(b)

// OuterClass.java: inner class demo public class OuterClass { private int data; /** A method in the outer class */ public void m() { // Do something } // An inner class class InnerClass { /** A method in the inner class */ public void mi() { // Directly reference data and method // defined in its outer class data++; m(); } } }

(c)


Inner Classes (cont.)

Inner classes can make programs simple and concise.

An inner class supports the work of its containing outer class and is compiled into a class named OuterClassName$InnerClassName.class. For example, the inner class InnerClass in OuterClass is compiled into OuterClass$InnerClass.class.


Inner Classes (cont.)

An inner class can be declared public, protected, or private subject to the same visibility rules applied to a member of the class.

An inner class can be declared static. A static inner class can be accessed using the outer class name. A static inner class cannot access nonstatic members of the outer class


Anonymous Inner Classes An anonymous inner class must always extend a superclass or

implement an interface, but it cannot have an explicit extends or implements clause.

An anonymous inner class must implement all the abstract methods in the superclass or in the interface.

An anonymous inner class always uses the no-arg constructor from its superclass to create an instance. If an anonymous inner class implements an interface, the constructor is Object().

An anonymous inner class is compiled into a class named OuterClassName$n.class. For example, if the outer class Test has two anonymous inner classes, these two classes are compiled into Test$1.class and Test$2.class.


Anonymous Inner Classes (cont.)

Inner class listeners can be shortened using anonymous inner classes. An anonymous inner class is an inner class without a name. It combines declaring an inner class and creating an instance of the class in one step. An anonymous inner class is declared as follows:

new SuperClassName/InterfaceName() { // Implement or override methods in superclass or interface // Other methods if necessary}

AnonymousListenerDemoAnonymousListenerDemo RunRun


Alternative Ways of Defining Listener Classes

There are many other ways to define the listener classes. For example, you may rewrite Listing 6.3 by creating just one listener, register the listener with the buttons, and let the listener detect the event source, i.e., which button fires the event.

DetectSourceDemoDetectSourceDemo RunRun


Alternative Ways of Defining Listener Classes

You may also define the custom frame class that implements ActionListener.

FrameAsListenerDemoFrameAsListenerDemo RunRun


Example: Handling Window Events

TestWindowEventTestWindowEvent RunRun

Objective: Demonstrate handling the window events. Any subclass of the Window class can generate the following window events: window opened, closing, closed, activated, deactivated, iconified, and deiconified. This program creates a frame, listens to the window events, and displays a message to indicate the occurring event.


MouseEvent

java.awt.event.MouseEvent

+getButton(): int

+getClickCount(): int

+getPoint(): java.awt.Point

+getX(): int

+getY(): int

Indicates which mouse button has been clicked.

Returns the number of mouse clicks associated with this event.

Returns a Point object containing the x and y coordinates.

Returns the x-coordinate of the mouse point.

Returns the y-coordinate of the mouse point.

java.awt.event.InputEvent

+getWhen(): long

+isAltDown(): boolean

+isControlDown(): boolean

+isMetaDown(): boolean

+isShiftDown(): boolean

Returns the timestamp when this event occurred.

Returns whether or not the Alt modifier is down on this event.

Returns whether or not the Control modifier is down on this event.

Returns whether or not the Meta modifier is down on this event

Returns whether or not the Shift modifier is down on this event.


Handling Mouse Events Java provides two listener interfaces, MouseListener and MouseMotionListener, to handle mouse events.

The MouseListener listens for actions such as when the mouse is pressed, released, entered, exited, or clicked.

The MouseMotionListener listens foractions such as dragging or moving themouse.


Handling Mouse Events

java.awt.event.MouseListener

+mousePressed(e: MouseEvent): void

+mouseReleased(e: MouseEvent): void

+mouseClicked(e: MouseEvent): void

+mouseEntered(e: MouseEvent): void

+mouseExited(e: MouseEvent): void

Invoked when the mouse button has been pressed on the source component.

Invoked when the mouse button has been released on the source component.

Invoked when the mouse button has been clicked (pressed and released) on the source component.

Invoked when the mouse enters the source component.

Invoked when the mouse exits the source component.

java.awt.event.MouseMotionListener

+mouseDragged(e: MouseEvent): void

+mouseMoved(e: MouseEvent): void

Invoked when a mouse button is moved with a button pressed.

Invoked when a mouse button is moved without a button pressed.


Example: Moving Message Using Mouse

Objective: Create a program to display a message in a panel. You can use the mouse to move the message. The message moves as the mouse drags and is always displayed at the mouse point.

MoveMessageDemoMoveMessageDemo RunRun


Handling Keyboard Events

keyPressed(KeyEvent e)

Called when a key is pressed.

keyReleased(KeyEvent e)

Called when a key is released.

keyTyped(KeyEvent e)

Called when a key is pressed and thenreleased.

To process a keyboard event, use the following handlers in the KeyListener interface:


The KeyEvent Class Methods:

getKeyChar() method

getKeyCode() method

Keys:Home VK_HOMEEnd VK_ENDPage Up VK_PGUPPage Down VK_PGDNetc...


The KeyEvent Class, cont.

java.awt.event.KeyEvent

+getKeyChar(): char

+getKeyCode(): int

Returns the character associated with the key in this event.

Returns the integer keyCode associated with the key in this event.

java.awt.event.InputEvent


Example: Keyboard Events Demo

Objective: Display a user-input character. The user can also move the character up, down, left, and right using the arrow keys.

KeyEventDemoKeyEventDemo RunRun


The Timer Class Some non-GUI components can fire events. The javax.swing.Timer class

is a source component that fires an ActionEvent at a predefined rate.

javax.swing.Timer

+Timer(delay: int, listener: ActionListener)

+addActionListener(listener: ActionListener): void

+start(): void

+stop(): void

+setDelay(delay: int): void

Creates a Timer with a specified delay in milliseconds and an ActionListener.

Adds an ActionListener to the timer.

Starts this timer.

Stops this timer.

Sets a new delay value for this timer.

The Timer class can be used to control animations. For example, you

can use it to display a moving message.

AnimationDemoAnimationDemo RunRun

liang, introduction to java programming, eighth edition, (c) 2011 pearson education, inc. all rights...

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