©TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 14...

©TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 14

Advanced GUI


Chapter 14 Objectives

After you have read and studied this chapter, you should be able to• Arrange GUI objects on a container,

using layout managers and nested panels.

• Write GUI application programs that process mouse events.

• Understand how the SketchPad class introduced in Chapter 2 is implemented.


Chapter 14 Objectives

After you have read and studied this chapter, you should be able to• Write GUI application programs with

JCheckBox, JRadioButton, JComboBox, JList, and JSlider objects.

• Develop programs using a variation of the model-view-controller (MVC) design pattern.


14.1 Handling Mouse Events

Mouse events include such user interactions as moving the mouse, dragging the mouse, and clicking the mouse buttons.

To study these events, we will define a subclass of JFrame that handles the left mouse button click events.

The subclass of JFrame we will define is named Ch14TrackMouseFrame.



A Ch14TrackMouseFrame object is an event source of mouse events. We will allow this object to be an event listener as well.

Its class must therefore implement the MouseListener interface.

Class Ch14TrackMouseFrame extends Frame implements MouseListener {

…

}



The MouseListener interface has five abstract methods:• mouseClicked• mouseEntered• mouseExited• mousePressed• mouseReleased

The argument to all five methods is an instance of MouseEvent.



The mouseClicked method is called every time the left mouse button is clicked, or pressed down and released.

The getX and getY methods of MouseEvent retrieve the x and y coordinate values of wherever the mouse is clicked.



If we want to detect the mouse button press and release separately, we can provide a method body to the mousePressed and mouseReleased methods, respectively.



The getClickCount method of MouseEvent will detect the number of mouse clicks performed, so different events may be triggered by a single click or double click, for example.



Implementing the MouseMotionListener interface will allow us to track mouse dragging.

The MouseMotionListener interface has two abstract methods:• mouseDragged• mouseMoved

The argument to both methods is an instance of MouseEvent.



When either the right or left mouse button is pressed, the event listener’s mousePressed method is called.

To determine which mouse button is pressed inside the mousePressed method, we call the isMetaDown method of MouseEvent.

The isMetaDown method returns true if the right button is pressed.



Similar to the mousePressed method, the mouseDragged method is called whether the mouse was dragged with the left or right button.

The isMetaDown method may also be used here to determine which button was used to drag the mouse.



We now have the tools to understand the implementation of the SketchPad class from Chapter 2.

Following is the fully implemented program.


14.1 Handling Mouse Events/*File: Ch14SketchPad.java*/import javax.swing.*;import java.awt.*;import java.awt.event.*;

class Ch14SketchPad extends JFrame implements MouseListener, MouseMotionListener {

private static final int FRAME_WIDTH = 450;private static final int FRAME_HEIGHT = 300;private static final int FRAME_X_ORIGIN = 150;private static final int FRAME_Y_ORIGIN = 250;

private int last_x;private int last_y;


14.1 Handling Mouse Eventspublic static void main(String[] args) { Ch14SketchPad frame = new Ch14SketchPad(); frame.setVisible(true); }

public Ch14SketchPad( ) { //set frame properties setTitle ("Chapter 14 SketchPad"); setSize ( FRAME_WIDTH, FRAME_HEIGHT ); setResizable( false ); setLocation ( FRAME_X_ORIGIN, FRAME_Y_ORIGIN );

setDefaultCloseOperation(EXIT_ON_CLOSE);

last_x = last_y = 0;

addMouseListener( this ); addMouseMotionListener( this );

}


14.1 Handling Mouse Events public void mousePressed( MouseEvent event ) { int x = event.getX(); int y = event.getY();

if ( event.isMetaDown() ) { //the right mouse button is pressed, so //erase the contents

Graphics g = getGraphics(); Rectangle r = getBounds(); g.clearRect(0, 0, r.width, r.height); g.dispose(); } else { //the left mouse button is pressed, //remember the starting point of a new //mouse drag

last_x = x; last_y = y; } }


14.1 Handling Mouse Events public void mouseClicked ( MouseEvent event ) { } public void mouseEntered ( MouseEvent event ) { } public void mouseExited ( MouseEvent event ) { } public void mouseReleased( MouseEvent event ) { }

public void mouseDragged( MouseEvent event ) { int x = event.getX(); int y = event.getY();

if ( !event.isMetaDown() ) { //don’t process the right button drag Graphics g = getGraphics(); g.drawLine(last_x, last_y, x, y); g.dispose(); last_x = x; last_y = y; } }public void mouseMoved ( MouseEvent event ) { }}


14.2 Layout Managers and Panels

For building practical GUI-based Java programs, we must learn how to use layout managers effectively.

We will begin by covering the three basic managers:• FlowLayout• BorderLayout• GridLayout



The default content pane of a frame is an instance of JPanel. We can place a JPanel inside another JPanel.

Each of these nesting panels may be assigned a different layout manager.

The capability of nesting panels with different layout managers presents opportunities for creating intricate layouts on a frame.



The most basic layout is java.awt.FlowLayout.

In this layout, GUI components are placed in left-to-right order. As a default, components on each line are centered.

When the frame containing the component is resized, the placement of the components is adjusted accordingly.



We first assign the desired layout manager to the container (in this case, the content pane of a frame) in the frame’s constructor.

Container contentPane = getContentPane();...contentPane.setLayout(new FlowLayout());

A container has a default layout manager assigned to it, but it is safer to explicitly assign the desired layout manager ourselves.



We then create five buttons and add them to the content pane.

JButton button1, button2, button3, button4, button5;

...

button1 = new JButton(“button1”);

...

contentPane.add(button1);

...


Fig. 14.1

Placement of five buttons by using FlowLayout when the frame is first opened and after the frame is resized.



The second layout manager is java.awt.BorderLayout.

This manager divides the container into five regions: • Center• North• South• East• West



We set the BorderLayout as

contentPane.setLayout(new BorderLayout());

And place GUI components with the second argument specifying the region:

contentPane.add(button1,BorderLayout.NORTH);contentPane.add(button1,BorderLayout.SOUTH);


Fig. 14.2

Placement of five buttons by using BorderLayout when the frame is first opened and after the frame is resized.


Fig. 14.3

Placement of two buttons by using BorderLayout. Buttons are placed on the center and east regions.



The default of BorderLayout has no gaps between the regions.

We can specify the amount of vertical and horizontal gaps between the regions in pixels.

contentPane.setLayout(new

BorderLayout(10, 20));



The third layout manager is java.awt.GridLayout.

This manager places GUI components on equal-sized N × M grids.

Components are placed in top-to-bottom, left-to-right order.


Fig. 14.4

Placement of five buttons by using GridLayout of two rows and three columns when the frame is first opened and after the frame is resized.



To create a GridLayout object, we pass two arguments:• Number of rows• Number of columns

contentPane.setLayout(new

GridLayout(2, 3));

We then place GUI components in the manner analogous to the one used for FlowLayout.



If the value provided for the number of rows is nonzero, the value we specify for the columns is irrelevant.

The layout will create the designated number of rows and adjust the number of columns so that all components will fit in the designated number of rows.


14.3 Effective Use of Nested Panels

It is possible, but very difficult, to place all GUI components on a single JPanel or other types of containers.

A better approach is to use multiple panels, placing panels inside other panels.



To illustrate this technique, we will create two sample frames that contain nested panels. The samples will provide the interface for playing Tic Tac Toe and HiLo.


Fig. 14.5

A sample frame that contains nested panels. Four JPanel objects are used in this frame.


Fig. 14.6

Another sample frame that contains nested panels. Five JPanel objects are used in this frame.



The topmost panel in Fig. 14.5 is the content pane of the frame. It has a border layout.

The content pane’s center region contains an instance of Ch14TicTacToePanel named gamePanel.



The content pane’s east region is occupied by an instance of another JPanel named controlPanel. A border layout is used for this panel.

The north region of controlPanel is occupied by another JPanel named scorePanel.

The south region is occupied by a JButton.



The layout for scorePanel is set to a grid layout with four grids, each occupied by a JLabel object.

The nesting relationship is illustrated in Fig. 14.7.


Fig. 14.7

This diagram shows how the panels of the frame in Fig. 14.5 are nested.



When we nest panels, it is useful to mark their borders.

The BorderFactory class contains many different border formats, such as• titled border• lowered bevel border• line border• etc.



We create a titled border by calling the class method createTitledBorder of the BorderFactory class.

scorePanel.setBorder(BorderFactory.createTitledBorder(“Scores: ”));

gamePanel.setBorder(BorderFactory.createLoweredBevelBorder());

Following is the program listing that creates the visual aspect of the program (i.e., there is no code for handling events or game logic).


14.3 Effective Use of Nested Panels/*File: Ch14NestedPanels1.java*/

import javax.swing.*;import java.awt.*;import java.awt.event.*;

class Ch14NestedPanels1 extends JFrame {


public static void main(String[] args) { Ch14NestedPanels1 frame = new Ch14NestedPanels1();

frame.setVisible(true);}


14.3 Effective Use of Nested Panelspublic Ch14NestedPanels1() { Container contentPane; Ch14TicTacToePanel gamePanel; JPanel controlPanel; JPanel scorePanel;

//set the frame properties setSize (FRAME_WIDTH, FRAME_HEIGHT); setTitle ("Program Ch14NestedPanels1"); setLocation (FRAME_X_ORIGIN, FRAME_Y_ORIGIN);

contentPane = getContentPane( ); contentPane.setLayout(new BorderLayout(10, 0));

gamePanel = new Ch14TicTacToePanel(); gamePanel.setBorder(BorderFactory.

createLoweredBevelBorder()); controlPanel = new JPanel(); controlPanel.setLayout(new BorderLayout( ));


14.3 Effective Use of Nested Panels contentPane.add(gamePanel, BorderLayout.CENTER); contentPane.add(controlPanel, BorderLayout.EAST);

scorePanel = new JPanel(); scorePanel.setBorder( BorderFactory.createTitledBorder("Scores:"));

scorePanel.setLayout(new GridLayout(2, 2)); scorePanel.add(new JLabel("Player 1:")); scorePanel.add(new JLabel(" 0")); scorePanel.add(new JLabel("Player 2:")); scorePanel.add(new JLabel(" 0"));

controlPanel.add(scorePanel,BorderLayout.NORTH); controlPanel.add(new JButton("New Game"), BorderLayout.SOUTH);

//register 'Exit upon closing' as a default //close operation setDefaultCloseOperation( EXIT_ON_CLOSE ); }}



For the second sample frame, we will use the nested panels shown in Fig. 14.8.

Again, this program illustrates only how the interface is built. It does not contain any game logic.


Fig. 14.8

The nested panels and associated layout managers for HiLoDisplay.


14.3 Effective Use of Nested Panels/*File: Ch14NestedPanels2.java*/import javax.swing.*;import java.awt.*;import java.awt.event.*;

class Ch14NestedPanels2 extends JFrame {


private final String ENTER = "Enter";private final String CANCEL = "Cancel";private final String BLANK = "";

private JTextField guessEntry;private JLabel hint;


14.3 Effective Use of Nested Panelspublic static void main(String[] args) { Ch14NestedPanels2 frame = new Ch14NestedPanels2();

frame.setVisible(true);}

public Ch14NestedPanels2( ) { JPanel guessPanel, hintPanel, controlPanel, buttonPanel; JButton enterBtn, cancelBtn;

Container contentPane; //set the frame properties setSize (FRAME_WIDTH, FRAME_HEIGHT); setTitle ("Program Ch14NestedPanels2"); setLocation (FRAME_X_ORIGIN, FRAME_Y_ORIGIN);

contentPane = getContentPane( ); contentPane.setLayout(new GridLayout(3, 1)); guessPanel = new JPanel();


14.3 Effective Use of Nested Panels guessPanel.setBorder(BorderFactory.createTitledBorder("Your Guess"));

guessPanel.add(guessEntry = new JTextField(10));

hintPanel = new JPanel(); hintPanel.setBorder(BorderFactory.createTitledBorder("Hint"));

hintPanel.add(hint = new JLabel("Let's Play HiLo"));

controlPanel = new JPanel(new BorderLayout()); buttonPanel = new JPanel(); buttonPanel.add(enterBtn = new JButton(ENTER)); buttonPanel.add(cancelBtn = new JButton(CANCEL)); controlPanel.add(buttonPanel,BorderLayout.SOUTH);

contentPane.add(guessPanel); contentPane.add(hintPanel); contentPane.add(controlPanel);}

}



There are two ways to approach designing the Tic Tac Toe board of N × N = N2 cells.

The panel handles the mouse click events, so every time the player clicks on a cell, a circle or cross is displayed.

However, the panel illustrated here does not contain any game logic.



The first approach is to compute the origin point (the top left corner) of each cell based on the dimension of the panel and the number of cells in the panel.

When we know the origin point of a cell, we can draw a circle or cross by using the drawLine or drawOval method.



When a cell is clicked, we get the x and y coordinates of the mouse click location and determine in which cell the mouse click event has occurred.

When we know the cell, we use its origin point to draw a circle or cross at the correct position and size.


Fig. 14.9

The approach not adopted here. The panel is divided into equal-size cells. A circle or cross can be drawn using the drawOval or drawLine method.



The second approach uses nested panels.

We will define two classes, Ch14TicTacToePanel and Ch14TicTacToeCell.

An instance of Ch14TicTacToePanel will contain N2 instances of Ch14TicTacToeCell, each representing a single cell in the board.



A Ch14TicTacToeCell object contains one component, an instance of JLabel.

Instead of assigning text to the JLabel, we assign an image icon to this object.

There are three image files:• circle.gif• cross.gif• blank.gif.



The Ch14TicTacToePanel’s main tasks are to handle the layout of N2 Cell objects and the mouse click events.

The GridLayout manager is perfect to use in this case.

Each cell is the source of mouse events, and the container of the cells is the mouse event listener.


14.4 Other GUI Components

You are already acquainted with Swing components JButton and JTextField.

We will now examine the basic capabilities of some additional Swing components that will be helpful in building your applications.



The JCheckBox class is used to represent check-box buttons.

Check-boxes are useful for presenting binary options (yes/no, true/false, etc.)

To create a check-box button with the text “Java,” we write

JCheckBox cbBtn = new JCheckBox(“Java”);


Fig. 14.10

A frame with four check box buttons and one pushbutton.



To check if a check-box button is selected or deselected, we call its isSelected method:

if (cbBtn.isSelected()){

System.out.println(“You can program in “ + cbBtn.getText());

}else{

...

}



A JCheckBox object generates both action events and item events.

It is not common to associate action listeners to JCheckBox objects.

An item event is generated when the state (selected or deselected) of a check-box button changes.



We can register an instance of a class that implements the ItemListener interface as an item listener of a JCheckBox object.

When an item event is generated, its itemStateChanged method is called.



The JRadioButton class is used to represent a radio button.

Radio buttons may be selected or deselected, but unlike check boxes, only one radio button in a group may be selected at any time.

When we select one radio button in a group, any other selected radio button in that group is deselected.


Fig. 4.11

A frame with four radio buttons and one pushbutton.



Radio buttons are useful in allowing the user to select one of a list of possible choices.

Radio buttons are used in a manner very similar to that of check boxes. They also generate both action and item events.

But radio buttons, unlike check boxes, must be added to a button group.



The JComboBox class presents a combo box.

This class, like JRadioButton, allows the user to select one of a list of possible choices.



The main difference between JComboBox and JRadioButton is in how the options are presented to the user.

The JComboBox presents the options to the user in a drop-down list.



We can construct a new JComboBox by passing an array of String objects:

String[] comboBoxItem = {“Java”, “C++”, “Smalltalk”, “Ada”};

JComboBox comboBox = new JComboBox(comboBoxItem);


Fig. 14.12

A frame with one combo box (drop-down list) and one pushbutton.



A JComboBox object generates action and item events.

To find out the currently selected item, we call the getSelectedItem method of JComboBox.



The JList class is useful when we need to display a list of items.

We can construct a JList object similarly to the way we construct a JComboBox object:

String[] names = {“Ape”, “Bat”, “Bee”, “Cat”, “Dog”, “Eel”, “Fox”, “Gnu”, “Hen”, “Man”, “Sow”, “Yak”};

JList list = new JList(names);


Fig. 14.13

A frame with one list and one pushbutton.



With JList, we have an option of specifying one of three selection modes:• single-selection• single-interval• multiple-interval



The single-selection mode allows the user to select only one item at a time.

The single-interval mode allows the user to select a single contiguous interval.

The multiple-interval mode is the default mode. It allows the user to select multiple contiguous intervals (each interval will include one or more items).



The following statements demonstrate how to set the different modes:

list.setSelectionMode(

ListSelectionModel.SINGLE_SELECTION);


ListSelectionModel.SINGLE_INTERVAL_

SELECTION);


ListSelectionModel.MULTIPLE_INTERVAL_

SELECTION);



The JSlider class represents a slider in which the user can move a nob to a desired position.

The position of the nob on the slider determines the selected value.



When a nob is moved, a JSlider object generates a change event (this event occurs when there is a change in the event source).

The event listener for this object must implement the ChangeListener interface.


Fig. 14.14

A frame with three vertical sliders for setting an RGB value.

©TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 14...

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