*Applet AWT

By Prof.ManikandanQMC, Chennai.manisankar27@gmail.com

*Out line: AWT WidgetsGraphical components-Label-TextComponent-Button-CheckBox-Choice-List-Container

*AWTGraphicsAWT - components for GUIs

*AWTAWT are used to make up a Graphical User Interface (GUI)The java.awt package provides a set of classes. These classes are platform independent.We construct a GUI by placing components within a container.-Normally, there are only two types of containers used:Frame - creates a complete windowPanel - a container and a component-Several Panels may be within a Frame, and within each Panel may be several components.

*The Component ClassThe Component class is an abstract class.

*The Component Classvoid paint (Graphics g)

-this method causes something to be painted in the component.

Example:

g.setFont(new Font("Arial",Font.BOLD,35));g.setColor(Color.BLUE);

import java.applet.*;import java.awt.*;/* */ public class RMKCOLORS extends Applet{public void paint(Graphics g){g.setFont(new Font("Arial",Font.BOLD,35));g.setColor(Color.BLUE);g.drawString("COLORS AND FONT PROGRAM", 100, 100);setBackground(Color.darkGray);g.setFont(new Font("Times New Roman",Font.ITALIC,30));g.setColor(Color.RED);g.drawString("DEVELOPED BY II BCA", 100, 120);}}

*

*LabelsA label is a component that will display a line of read-only text on the screen.It has three constructors:-Label()center alignment and no text-Label( String text)a center aligned Label object displaying the text given-Label( String text, int alignment)Label with the given text and alignment specified as eitherLabel. LEFT, Label. CENTER, and Label. RIGHTAfter you have a Label object, you can use methodsdefined in the Label class to get and set various attributes.

*Label ExampleExample:

import java. awt.*;public class LabelExample extends java. applet. Applet{public void init() {setLayout( new GridLayout( 1, 1));add( new Label( left, Label. LEFT));add( new Label( center, Label. CENTER));add( new Label( right, Label. RIGHT));}//end of init}//end of LabelExample

row numbercolumn number

*Text Component ClassThere are two Types: TextField and TextArea that are very similar to each other. so the data and methods that are common to both were removed and placed into the TextComponent class.So TextField and TextArea are both subclasses of TextComponentThere are few methods that are inherited byTextField and TextArea-String getText()returns a copy of the current contents of the component-void setText( String text)sets the current text to what is specified in by the argument

*TextField ClassText fields are a box into which a single line of text may be placed.

Text fields are different from labels in that they can beedited.

*TextArea ClassText areas are like text fields except they can handle largeramounts of text.

Text areas can be given any width and height and have scroll bars by default.

*TextArea ClassThere are five constructors for a TextArea object:-TextArea()creates an empty TextArea object

-TextArea( int rows, int columns)creates an empty text area with the given number of rows andcolumns( chars)

-TextArea( String text)creates a default sized text area containing the argument string

-TextArea( String text, int rows, int columns)creates a text area displaying the given string with the size specified

*TextArea Class-TextArea( String text, int rows, int columns, int scrollbars)-There are 4 constant arguments that can be used:TextArea. SCROLLBARS_ BOTHTextArea. SCROLLBARS_ NONETextArea. SCROLLBARS_ HORIZONTAL_ ONLYTextArea. SCROLLBARS_ VERTICAL_ ONLY-The default is for both horizontal and vertical scrollbars to be displayed.

*TextArea Class ExampleAn example:

import java. awt.*;public class TextAreaExample extends java. applet. Applet {public void init() {String str = This is an example for a TextArea that \n+spans multiple lines. \n;add( new TextArea( str));}//end of init}//end of TextAreaExample

*Button ClassButtons are a simple UI component that triggers some actionThere are two constructors for a Button object:-Button()creates an empty button with no label-Button( String label)creates a button with the given string as a labelAfter creating a Button object, you can get the value of the Buttons label by using the getLabel() method whichreturns a String.Using the setLabel() method, you can set the label of the button by passing in a String value.

*Button ClassAn Example:

import java. awt.*;public class ButtonExample extends java. applet. Applet {public void init() {add( new Button( Rewind));add( new Button( Fast Forward));add( new Button( Play));add( new Button( Stop));add( new Button( Pause));}//end of init}//end of ButtonExample

*Checkbox ClassCheck boxes are UI components that have two states: onand off (or checked and unchecked, or true and false)used to indicate optional features of some other action.Check boxes can be used in two ways:-Nonexclusivegiven a series of checkboxes, any of them can be selected;can be checked or unchecked independently of each other-Exclusivegiven a series of checkboxes, only one can be selected at any one time, also known as radio buttons or checkboxgroups

Jan. 2004*Checkbox ClassThere are five constructors:-Checkbox()creates a Checkbox with no label and false-Checkbox( String label)creates a Checkbox with the given label and initialized to false-Checkbox( String label, boolean state)creates a Checkbox with the given label and state-Checkbox( String label, boolean state, CheckboxGroup group)-Checkbox( String label, CheckboxGroup group, boolean state)The last two create a Checkbox with the label and state specified as well as specifying a group that this Checkbox will belong to.

*Checkbox ClassAn Example:import java. awt.*;public class CheckboxExample extends java. applet. Applet {public void init() {setLayout( new FlowLayout( FlowLayout. LEFT));add( new Checkbox( Red));add( new Checkbox( Orange));add( new Checkbox( Yellow));add( new Checkbox( Green));add( new Checkbox( Blue));add( new Checkbox( Indigo));add( new Checkbox( Violet));}//end of init}//end of CheckboxExample

*CheckBoxGroupsA CheckboxGroup is a collection of Checkboxes in whichonly one of them can be selected at one time; - also known as radio buttonsTo create a series of radio buttons, first create an instance of CheckboxGroup-ChecboxGroup cbg = new CheckboxGroup();Then create and add the radio buttons into the group-use either of the following two methods:Checkbox( String label, boolean state, CheckboxGroup group)Checkbox( String label, CheckboxGroup group, boolean state)

*CheckBoxGroupsAn Example:import java. awt.*;public class CheckboxGroupExample extends java. applet. Applet {public void init() {setLayout( new FlowLayout( FlowLayout. LEFT));CheckboxGroup cbg = new CheckboxGroup();add( new Checkbox( One, false, cbg));add( new Checkbox( Two, false, cbg));add( new Checkbox( Three, true, cbg));add( new Checkbox( Four, false, cbg));}//end of init}//end of CheckboxGroupExample

*CheckBoxGroupsSince CheckboxGroups only allow one button to be selected at one time, the last Checkbox to be added to the group with the state being true will be the one selected by default.

So in the previous example, radio button with the label three would be selected.

*Choice ClassChoice menus are more complex than labels, buttons, orcheckboxes.Choice menus are pop-up or pull-down lists in which an item can be selected.To create a Choice menu, we first need an instance of the Choice class and then add items to it.The items added are enumerated from top to bottomstarting with the index 0.One of the methods in this class to make note of is:-String getSelectedItem()returns the text of the current selection

*Choice ClassAn Example:import java. awt.*;public class ChoiceExample extends java. applet. Applet {public void init() {Choice c = new Choice();c. add( Red);c. add( Orange);c. add( Yellow);c. add( Green);c. add( Blue);c. add( Indigo);c. add( Violet);add( c);}//end of init}//end of ChoiceExample

*List ClassA List is functionally similar to a Choice menu in that itlets you choose from a list, but Lists do not pop-up, they are permanently displayed on the screen.

You can choose more than one item on the List if thatcapability is enabled.

List items are enumerated from top to bottom starting at index 0 just like a Choice menu.

*List ClassThere are three constructors for a List object:-List()creates a default sized List object in single selection mode-List( int rows)creates a List object in single selection mode with the number of rows given-List( int rows, boolean multipleselection)creates a List object with the specified number of rows. The List is in multiple selection mode if the boolean argument is true and single selection otherwise.