CSCI213 Spring2013 Lectures Java GUI

7/30/2019 CSCI213 Spring2013 Lectures Java GUI

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Java GUI Basics

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CSCI 213: Java GUISpring 2013

Objectives

Introduction to java GUI basics To distinguish between Swing and AWT To describe the Java GUI API hierarchy To create user interfaces using frames, panels, and

simple GUI components

To understand the role of layout managers To use the FlowLayout, GridLayout, and BorderLayout

managers to layout components in a container To use JPanel as subcontainers To specify colors and fonts using the Color and Font

classes

To apply common features such as borders, tool tips,fonts, and colors on Swing components

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Graphical user interface (GUI)

Presents a user-friendly mechanism forinteracting with an application Often contains title bar, menu bar

containing menus, buttons and comboboxes

Built from GUI components

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Elements of GUI Programming

ComponentsVisual objects that appear on the screen

Layouts Control over the positioning of components

within a container

Events Responses to user actions

Graphics Lines, shapes, colors, fonts, etc.

All are encapsulated in Java Classes and Packages4

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Graphical Componentsbutton menus title bar menu bar combo box

scroll

bars

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mp e - ase nput utputwith JOptionPane

Dialog boxes Used by applications to interact with the user Provided by Javas JOptionPane class

Contains input dialogs and message dialogs

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1 // Example!2 // Addition program that uses JOptionPane for input and output.!3 import javax.swing.JOptionPane; // program uses JOptionPane !4 !5 public class Addition6 {7 public static void main( String args[] )8 {9 // obtain user input from JOptionPane input dialogs !10 String firstNumber =11 JOptionPane.showInputDialog( "Enter first integer" );12 String secondNumber =13 JOptionPane.showInputDialog( "Enter second integer" );14 !15 // convert String inputs to int values for use in a calculation!16 int number1 = Integer.parseInt( firstNumber );17 int number2 = Integer.parseInt( secondNumber );18 !19 int sum = number1 + number2; // add numbers !20 !21 // display result in a JOptionPane message dialog !22 JOptionPane.showMessageDialog( null, "The sum is " + sum,23 "Sum of Two Integers", JOptionPane.PLAIN_MESSAGE );24 } // end method main !25 } // end class Addition !

Show input dialog to receive first

integer

Show input dialog to receive

second integer

Show message dialog to output sum

to user

Example

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Input dialog displayed by lines 1011

Input dialog displayed by lines 1213

Message dialog displayed by lines 2223

Text field in which

the user types a

value

Prompt to the user

hen the user clicksOK,showInputDialog returns

to the program the100typed by the user as a

String . The programmust convert the String

to an int

title bar

When the user clicksOK,the

message dialog is dismissed

(removed from the screen)

Example (2)

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JOptionPane static constants

Message dialog type Icon Description

ERROR_MESSAGE A dialog that indicates an error to the user.

INFORMATION_MESSAGE A dialog with an informational message t o theuser.

WARNING_MESSAGE A dialog warning the user of a potentialproblem.

QUESTION_MESSAGE A dialog that poses a question to the user. Thisdialog normally requires a response, s uch as

clicking aYes or a No button.

PLAIN_MESSAGE no icon A dialog that contains a message, but no icon.

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Most Used Components

Component Description

JLabel Displays uneditable text or icons.JTextField Enables user to enter data from the keyboard. Can also be used to

display editable or uneditable text.

JButton Triggers an event when clicked with the mouse.JCheckBox Specifies an option that can be selected or not selected.JComboBox Provides a drop-down list of items from which the user can make a

selection by clicking an item or possibly by typing into the box.

JList Provides a list of items from which the user can make a selection byclicking on any item in the list. Multiple elements can be selected.

JPanel Provides an area in which components can be placed and organized.Can also be used as a drawing area for graphics.

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Creating GUI Objects// Create a button with text OKJButton jbtOK = new JButton("OK");

// Create a label with text "Enter your name: "

JLabel jlblName = new JLabel("Enter your name: ");

// Create a text field with text "Type Name Here"

JTextField jtfName = new JTextField("Type Name Here");

// Create a check box with text boldJCheckBox jchkBold = new JCheckBox("Bold");

// Create a radio button with text red

JRadioButton jrbRed = new JRadioButton("Red");

// Create a combo box with choices red, green, and blue

JComboBox jcboColor = new JComboBox(new String[]{"Red","Green", "Blue"});

Button

Label Textfield

CheckBox

RadioButton

ComboBox

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Swing vs. AWT So why do the GUI component classes have a prefix J?

Q: instead of JButton, why not name it simply Button?

A: there is a class already named Button in the java.awt package When Java was introduced, the GUI classes were bundled in a library known as

the Abstract Windows Toolkit (AWT).

For every platform on which Java runs, the AWT components are automaticallymapped to the platform-specific components through their respective agents,known as peers

AWT is fine for developing simple graphical user interfaces, but not fordeveloping comprehensive GUI projects

Besides, AWT is prone to platform-specific bugs its peer-based approach relies heavily on the underlying platform.

With the release of Java 2, the AWT user-interface components were replacedby a more robust, versatile, and flexible library known as Swing components

Swing components are less dependent on the target platform and use less ofthe native GUI resource. For this reason, Swing components that dont rely onnative GUI are referred to as lightweight components, and AWT componentsare referred to as heavyweight components.

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GUI Class Hierarchy (Swing)

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Container Classes

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GUI Helper Classes

The helper classes are notsubclasses of Component. Theyare used to describe theproperties of GUI componentssuch as colors, fonts, anddimension.

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Swing GUI Components

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omponents overe n t e r eVersion

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omponents overe n t eComprehensive Version

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AWT (Optional)

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Frames

Frame is a window that is not containedinside another window. Frame is the basisto contain other user interfacecomponents in Java GUI applications.

The JFrame class can be used to createwindows.

For Swing GUI programs, use JFrame classto create widows.

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Frames with Components

A Frame is a container. Therefore it can containother components (like buttons, text fields, etc.) Components are added to the content pane of a

frame.

The content pane is the grey area in the Framewindow.

A simplistic way to look at containment is this:A JFrame contains:

A menu barA content pane

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A Picture of Frame Containment

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Creating Framesimport javax.swing.*;public class MyFrame {

public static void main(String[] args) {

JFrame frame = new JFrame("Test Frame");frame.setSize(400, 300);

frame.setVisible(true);frame.setDefaultCloseOperation(

JFrame.EXIT_ON_CLOSE);

}}!

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Adding Components into a Frame!// Add a button into the frameframe.getContentPane().add(

new JButton("OK"));Title bar

Contentpane

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Content Pane Delegation in JDK1.5!

// Add a button into the frameframe.getContentPane().add(

new JButton("OK"));Title bar

Contentpane

// Add a button into the frameframe.add(

new JButton("OK"));

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Adding a JButton to a Frameimport javax.swing.*;public class MyFrame {

public static void main(String[] args) {

JFrame frame = new JFrame("Test Frame");

JButton okBtn = new Jbutton(Ok));

frame.add(okBtn);

frame.setSize(400, 300);

frame.setVisible(true);frame.setDefaultCloseOperation(

JFrame.EXIT_ON_CLOSE);

}}!

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JFrame Classjavax.swing.JFrame

+JFrame()

+JFrame(title: String)

+setSize(width: int, height: int): void

+setLocation(x: int, y: int): void

+setVisible(visible: boolean): void

+setDefaultCloseOperation(mode: int): void

+setLocationRelativeTo(c: Component):

void

+pack(): void

Creates a default frame with no title.

Creates a frame with the specified title.

Specifies the size of the frame.

Specifies the upper-left corner location of the frame.

Sets true to display the frame.

Specifies the operation when the frame is closed.

Sets the location of the frame relative to the specified component.

If the component is null, the frame is centered on the screen.

Automatically sets the frame size to hold the components in the

frame.

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Layout Managers

Javas layout managers provide a level of abstraction toautomatically map your user interface on all windowsystems.

Control the placement of components on the container. The UI components are placed in containers. Each

container has a layout manager to arrange the UIcomponents within the container.

This is an alternative to hardcoding the pixel locations ofthe components.

Advantage: resizing the container (frame) will notocclude or distort the view of the components.

Layout managers are set in containers using thesetLayout(LayoutManager) method in a container.

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Kinds of Layout Managers

Basic layouts: FlowLayout GridLayout BorderLayout

Other layout managers: Containers Layout Managers, and Borders

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FlowLayout Places components sequentially (left-to-right) in

the order they were added

Components will wrap around if the width of thecontainer is not wide enough to hold them all in arow.

Default for applets and panels, but not for frames Options:

left, center (this is the default), or right Typical syntax: in your Frame classs constructor

setLayout(new FlowLayout(FlowLayout.LEFT)) OR setLayout(new

FlowLayout(FlowLayout.LEFT,hgap,vgap))

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Resizing the frame causes thecomponents to wrap aroundwhen necessary.

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The FlowLayout Class

java.awt.FlowLayout

-alignment: int

-hgap: int

-vgap: int

+FlowLayout()

+FlowLayout(alignment: int)

+FlowLayout(alignment: int, hgap:int, vgap: int)

The alignment of this layout manager (default: CENTER).

The horizontal gap of this layout manager (default: 5 pixels).

The vertical gap of this layout manager (default: 5 pixels).

Creates a default FlowLayout manager.

Creates a FlowLayout manager with a specified alignment.

Creates a FlowLayout manager with a specified alignment,horizontal gap, and vertical gap.

The get and set methods for these data fields are provided inthe class, but omitted in the UML dia ram for brevit .

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GridLayout

Arranges components into rows and columns In Frames constructor: setLayout (new GridLayout(rows, columns))

OR

setLayout(new GridLayout(rows,columns,hgap,vgap)) Components will be added in order, left to right,

row by row

Components will be equal in sizeAs container is resized, components will resize

accordingly, and remain in same grid

arrangement

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Resizing the frame causes thecomponents to resize andmaintain their same grid pattern.

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The GridLayout Class

java.awt.GridLayout

-rows: int

-columns: int

-hgap: int

-vgap: int

+GridLayout()

+GridLayout(rows: int, columns: int)

+GridLayout(rows: int, columns: int,hgap: int, vgap: int)

The number of rows in this layout manager (default: 1).

The number of columns in this layout manager (default: 1).

The horizontal gap of this layout manager (default: 0).

The vertical gap of this layout manager (default: 0).

Creates a default GridLayout manager.

Creates a GridLayout with a specified number of rows and columns.

Creates a GridLayout manager with a specified number of rows andcolumns, horizontal gap, and vertical gap.

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

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BorderLayout Arranges components into five areas: North, South, East,

West, and Center In the constructor:

setLayout(new BorderLayout())OR

setLayout(new BorderLayout(hgap,vgap)) for each component:

add (the_component, region) do for each area desired:

BorderLayout.EAST, BorderLayout.SOUTH, BorderLayout.WEST,BorderLayout.NORTH, or BorderLayout.CENTER

Behavior: when the container is resized, the componentswill be resized but remain in the same locations.

NOTE: only a maximum of five components can beadded and seen in this case, one to each region.

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Resizing the

frame causesthe componentsto resize andmaintain theirsame regions.

NOTE: the CENTER regiondominates the sizing.

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The BorderLayoutClass

java.awt.BorderLayout

-hgap: int

-vgap: int

+BorderLayout()

+BorderLayout(hgap: int, vgap: int)

The horizontal gap of this layout manager (default: 0).

The vertical gap of this layout manager (default: 0).

Creates a default BorderLayout manager.

Creates a BorderLayout manager with a specified number of

horizontal gap, and vertical gap.

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

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Using Panels as Sub-Containers

JPanel is a class of special components that cancontain other components.As containers, JPanels can have their own layout

managers.

This way, you can combine layouts within thesame frame by adding panels to the frame andby adding other components to the panels.

Therefore, like JFrames, you can use thesemethods with JPanels:

add() to add components to the panel setLayout() to associate a layout manager for the

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Testing Panels

This example uses panels to organizecomponents. The program creates a userinterface for a Microwave oven.

A button

A textfield

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buttons

frame

p2

p1

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The Color ClassYou can set colors for GUI components by using thejava.awt.Color class. Colors are made of red, green,and blue components, each of which is representedby a byte value that describes its intensity, rangingfrom 0 (darkest shade) to 255 (lightest shade). Thisis known as the RGB model.

Color c = new Color(r, g, b);r,g, and

bspecify a color by its red, green, and

blue components. !Example:

Color c = new Color(228, 100, 255);

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Standard ColorsThirteen standard colors (black, blue, cyan, darkGray,

gray, green, lightGray, magenta, orange, pink, red,white, yellow) are defined as constants in

java.awt.Color.

The standard color names are constants, but they arenamed as variables with lowercase for the first wordand uppercase for the first letters of subsequent words.Thus the color names violate the Java namingconvention.

Since JDK 1.4, you can also use the new constants:BLACK, BLUE, CYAN, DARK_GRAY, GRAY, GREEN,LIGHT_GRAY, MAGENTA, ORANGE, PINK, RED, WHITE,and YELLOW.

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Setting Colors

You can use the following methods to set thecomponents background and foreground colors:

setBackground(Color c)

setForeground(Color c)

Example:

jbt.setBackground(Color.yellow);

jbt.setForeground(Color.red);

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The Font Class

Font myFont = new Font(name, style, size);

Example:Font myFont = new Font("SansSerif ", Font.BOLD, 16);Font myFont = new Font("Serif", Font.BOLD+Font.ITALIC, 12);

JButton jbtOK = new JButton("OK);

jbtOK.setFont(myFont);

Font NamesStandard font namesthat are supported inall platforms are:SansSerif, Serif,Monospaced, Dialog,or DialogInput.

Font StyleFont.PLAIN (0),Font.BOLD (1),Font.ITALIC (2), andFont.BOLD +Font.ITALIC (3)

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Finding All Available Font

NamesGraphicsEnvironment e =

GraphicsEnvironment.getLocalGraphicsEnvironment();

String[] fontnames =e.getAvailableFontFamilyNames();

for (int i = 0; i < fontnames.length; i++)

System.out.println(fontnames[i]);

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Using Panels as Sub-Containers

Panels act as sub-containers for grouping userinterface components.

It is recommended that you place the userinterface components in panels and place the

panels in a frame. You can also place panels in a

panel.

To add a component to JFrame, you actually addit to the content pane of JFrame. To add a

component to a panel, you add it directly to the

panel using the add method.

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Creating a JPanel

You can use new JPanel() to create a panel with adefault FlowLayout manager or new

JPanel(LayoutManager) to create a panel with the

specified layout manager

Use the add(Component) method to add acomponent to the panel. For example,

JPanel p = new JPanel();

p.add(new JButton("OK"));

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Testing Panels Example

This example uses panels to organizecomponents. The program creates a userinterface for a Microwave oven.!

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Common Features of Swing Components

java.awt.Container

+add(comp: Component): Component

+add(comp: Component, index: int): Component

+remove(comp: Component): void

+getLayout(): LayoutManager

+setLayout(l: LayoutManager): void

+paintComponents(g: Graphics): void

Adds a component to the container.

Adds a component to the container with the specified index.

Removes the component from the container.

Returns the layout manager for this container.

Sets the layout manager for this container.

Paints each of the components in this container.

java.awt.Component

-font: java.awt.Font

-background: java.awt.Color

-foreground: java.awt.Color

-preferredSize: Dimension

-visible: boolean

+getWidth(): int

+getHeight(): int

+getX(): int

+getY(): int

The font of this component.

The background color of this component.

The foreground color of this component.

The preferred size of this component.

Indicates whether this component is visible.

Returns the width of this component.

Returns the height of this component.

getX() and getY() return the coordinate of the components

upper-left corner within its parent component.

javax.swing.JComponent

-toolTipText: String

-border: javax.swing.border.Border

The tool tip text for this component. Tool tip text is displayed when

the mouse points on the component without clicking.

The border for this component.

The get and set methods for these data fields are provided in

the class, but omitted in the UML diagram for brevity.

The get and set methods for these data fields are provided in

the class, but omitted in the UML diagram for brevity.

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Image IconsJava uses the javax.swing.ImageIcon class torepresent an icon. An icon is a fixed-size picture;

typically it is small and used to decoratecomponents. Images are normally stored in imagefiles. You can use new ImageIcon(filename) toconstruct an image icon. For example, the followingstatement creates an icon from an image file abc.gif

in the image directory under the current class path:ImageIcon icon = new ImageIcon("image/abc.gif");

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CSCI213 Spring2013 Lectures Java GUI

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Transcript of CSCI213 Spring2013 Lectures Java GUI