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Control Fundamentals

Labels

Using Buttons Applying Check Boxes

CheckBox Group

Choice Controls

Using Lists

Managing Scroll Bars

Using a Text Field

Using a TextArea

Understanding Layout Managers

, Menu Bars and Menus

Dialog Boxes

FileDialog

Handling Events by Extending AWT Components.

TOPICS

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The AWT supports the following types of controls:

Control Fundamentals

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To add a control to a window :

1. first create an instance of the desired control

2. then add it to a window by calling add( ) , which

is defined by Container.

Adding and Removing Controls

Component add(Component compObj)

compObjAn instance of the control that you want to add

A reference to compObj is returned.

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To remove a control , call remove( ). This method is

also defined by Container

Adding and Removing Controls

void remove(Component obj)

compObjA reference to the control that you want to remove

You can remove all controls by calling removeAll( )

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In general, your program simply implements the

appropriate interface and then registers an event listener

for each control that you need to monitor.

Responding to Controls

HeadlessException

Generated by all constructors of the controls

Thrown when code that is dependent on a keyboard,

display, or mouse is called in an environment that does

not support a keyboard, display, or mouse.

Added by java 1.4

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A label is an object of type Label, and it contains a

string, which it displays. Label defines the followingconstructors:

Labels

1. Label( )

2. Label(String str)

3. Label(String str, int how)

1. The first version creates a blank label.

2. The second version creates a label that contains the

string specified by str.(left-justified.)

3. The third version creates a label that contains the string

specified by strusing the alignment specified by how

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The value ofhow must be one of these three constants:1. Label.LEFT,2. Label.RIGHT,3. Label.CENTER.

Labels

void setText(String str) set or change the text in a label

StringgetText( ) obtain the current label

void setAlignment(int how) set the alignment of the string

intgetAlignment( ) obtain the current alignment

how must be one of the alignment constants

shown above

Methods :

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The following example creates three labels and adds them to an

applet:

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Following is the window created by the LabelDemo applet

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Using Buttons

The most widely used control is the push button.

A push button is a component that contains a label and that

generates an event when it is pressed. Push buttons are objects

of type Button.

Constructors:

1. Button( )creates an empty button

2. Button(String str) creates a button that contains stras a label.

Methods :1. void setLabel(String str) set the label

2. String getLabel( ) retrieve the label

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Handling Buttons

Each time a button is pressed, an Action Event is generated.

Each listener implements theActionListenerinterface.

This interface defines the actionPerformed( ) method, which

is called when an event occurs.

An ActionEvent object is supplied as the argument to this

method.

The label is obtained by calling getActionCommand() on

ActionEvent Object

(ActionEvent contains both a reference to the button that generated the

event and a reference to the string that is the label of the button)

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Handling Buttons

Here is an example that creates three buttons labeled Yes, No, and Undecided.

Each time one is pressed, a message is displayed that reports which button has been

pressed.

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Sample output

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Handling Buttons

You can also determine which button has been pressed, by

comparing the object obtained from thegetSource( ) method

To do this, you must keep a list of the objects when they are added.

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Handling Buttons

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Applying Check Boxes

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A check box is a control that is used to turn an option on or off

There is a label associated with each checkbox that describes

what option the box represents

Check boxes are objects of the Checkbox class.

Constructors:

1. Checkbox( )

2. Checkbox(String str)

3. Checkbox(String str, boolean on)

4. Checkbox(String str, boolean on, CheckboxGroup cbGroup)

5. Checkbox(String str, CheckboxGroup cbGroup, boolean on)

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1. The first form creates a check box whose label is initially

blank. The state of the check box is unchecked2. The second form creates a check box whose label is

specified by str. The state of the check box is unchecked

3. The third form allows you to set the initial state of the

check box.

4. The fourth and fifth forms create a check box whose label

is specified by str and whose group is specified by

cbGroup. If this check box is not part of a group, then

cbGroup must be null.

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Methods :

1. booleangetState( ) retrieve the current state of a

check box

2. void setState(boolean on) To set its state

3. StringgetLabel( ) obtain the current label

associated with a check box

4. void setLabel(String str) To set the label

ifon is true, the box is checked. If it is false, the box is

cleared.

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Handling Check Boxes

Each time a check box is selected or deselected, an

item eventis generated

Your program must implement ItemListenerInterface

This interface defines the itemStateChanged( ) method

An ItemEvent object is supplied as the argument to this

method.

An ItemEvent object contains information about the

event

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The following program creates four check boxes. The initial

state of the first box is checked. The status of each check

box is displayed. Each time you change the state of a check

box, the status display is updated.

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Sample output

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CheckboxGroup

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CheckboxGroup (radio buttons)

A set of mutually exclusive check boxes in which one and only one

check box in the group can be checked at any one time.

Check box groups are objects of type CheckboxGroup

Constructor :CheckboxGroup() creates an empty group

Methods:

1. Checkbox getSelectedCheckbox( ) get status

2. void setSelectedCheckbox(Checkbox which) set a check box

which the check box that you want to be selected

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First define the group to which they will belong and then specify

that group when you construct the check boxes.

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Output generated by the CBGroup applet is shown

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Choice Controls

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Choice Controls

A Choice control is a form of menu.

The Choice class is used to create a pop-up list of items from

which the user may choose

Each item in the list is a string that appears as a left-justified

label in the order it is added to the Choice object

Constructor (default):

Choice () creates an empty list.

Choice Controls

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Choice Controls

Methods :

1. void add(String name) add a selection to the list

2. String getSelectedItem( ) returns a string containing the

name of the item

3. intgetSelectedIndex( )returns the index of the item

4. intgetItemCount( ) obtain the number of items in the list

5. void select(int index) select an item with a zero-based

integer index

6. void select(String name) select an item with a string

7. StringgetItem(int index) obtain the name associated with

the item at the given index.

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Handling Choice Lists

Each time a choice is selected, an item event is

generated.

Each listener implements theItemListenerinterface

That interface defines the itemStateChanged( )

method

An ItemEvent object is supplied as the argument to

this method.

dli h i i

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Handling Choice Lists

Here is an example that creates two Choice menus. One selects the

operating system. The other selects the browser.

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Using Lists

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Using Lists

The List class provides a compact, multiple-choice, scrolling

selection list

Constructors :

1. List( ) creates a List control that allows only one item to be

selected at any one time.

2. List(int numRows) The value of numRows specifies the

number of entries in the list that will always be visible.

3. List(int numRows, boolean multipleSelect) If

multipleSelect is true, then the user may select two or more

items at a time.

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Methods :

1. void add(String name) adds items to the end of

the list

2. void add(String name, int index) adds the item

at the index specified by index

3. String getSelectedItem( ) returns a string

containing the name of the item.

4. int getSelectedIndex() returns the index of the

item

Using Lists

M h d

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Methods :

5. String[ ] getSelectedItems( ) returns an array

containing the names of the currently selected items.

6. int[ ] getSelectedIndexes( ) returns an array

containing the indexes of the currently selected items.

7. int getItemCount( ) obtain the number of items in the

list

8. void select(int index)

set the currently selected item

9. String getItem(int index) obtain the name associated

with the item at the index

Handling Lists

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you will need to implement the ActionListener interface

Each time a List item is double-clicked, an ActionEvent object isgenerated

Its getActionCommand( ) method can be used to retrieve the

name of the newly selected item

Each time an item is selected or deselected with a single click,

an ItemEvent object is generated

Its getStateChange( ) method can be used to determine

whether a selection or deselection triggered this event

getItemSelectable( ) returns a reference to the object that

triggered this event.

Handling Lists

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Here is an example that converts the Choice controls in the preceding

section into List components, one multiple choice and the other

single choice:

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g g

Constructors

1. Scrollbar() creates a vertical scroll bar.2. Scrollbar(int style)

style specifies the orientation . style can be

Scrollbar.VERTICAL

Scrollbar.HORIZONTAL

3. Scrollbar(int style, int initialValue, int thumbSize, int min, int max)

initialValuethe initial value of the scroll bar

thumbSize The number of units represented by the height of the thumb

min , max The minimum and maximum values for the scroll bar


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g g

Methods :

1. void setValues(int initialValue, int thumbSize, int min, int max)

set its parameters

2. int getValue( ) obtain the current value of the scroll bar

3. void setValue(int newValue) set the current value

4. int getMinimum( ) retrieve the minimum values

5. int getMaximum( ) retrieve the maximum values

6. void setUnitIncrement(int newIncr)change the increment (default : 1)

7. void setBlockIncrement(int newIncr) page-up and page-down increments

(default : 10)

Handling Scroll Bars

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Interaction with a scroll bar, generates an Adjustment Event

you need to implement the AdjustmentListener interface

This interface defines adjustmentValueChanged() method

which takes AdjustmentEvent object as the argument

getAdjustmentType() ofAdjustmentEvent can be used to

determine the type of the adjustment.

g


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g

The types of adjustment events are as follows:


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The following example creates both a vertical and a horizontal scroll bar. If you

drag the mouse while inside the window, the coordinates of each drag event

are used to update the scroll bars. An asterisk is displayed at the current drag

position.

g


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g


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Sample output

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Using a TextField

Using a TextField

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The TextField class implements a single-line text-entry area,

usually called an edit control.

TextField is a subclass ofTextComponent

Constructors :

1. TextField( ) creates a default text field

2. TextField(int numChars) creates a text field that is

numChars characters wide

3. TextField(String str)initializes the text field with the string

4. TextField(String str, int numChars) initializes a text field

and sets its width

Using a TextField

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Using a TextField

Methods

1. String getText( ) obtain the curent string

2. void setText(String str) To set the text

3. String getSelectedText( ) select a portion of the text

4. void select(int startIndex, int endIndex) obtain the

currently selected text

Using a TextField

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Using a TextField

Methods

5. void setEditable(boolean canEdit) if canEdit is true, thetext may be changed. If it is false, the text cannot be altered

6. boolean isEditable( ) determine editability7. void setEchoChar(char ch) disable the echoing of the

characters

8. boolean echoCharIsSet( ) check a text field to see if it is inthis mode

9. char getEchoChar( ) retrieve the echo character

Handling a TextField

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Handling a TextField

Text Field generates Action Event when ENTER key is pressed.

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Sample output

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Using a TextArea

Using a TextArea

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Using a TextArea

AWT includes a simple multiline editor called TextArea

TextArea is a subclass ofTextComponent

Constructors :

1. TextArea( )

2. TextArea(int numLines, int numChars)

3. TextArea(String str)

4. TextArea(String str, int numLines, int numChars)

5. TextArea(String str, int numLines, int numChars, int sBars)

Using a TextArea

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Using a TextArea

Constructors :

numLines specifies the height, in lines,

numCharsspecifies its width, in characters.

str Initial text

sBars must be one of these values :

SCROLLBARS_BOTH

SCROLLBARS_NONE

SCROLLBARS_HORIZONTAL_ONLY

SCROLLBARS_VERTICAL_ONLY

Using a TextArea

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Using a TextArea

Methods :

Supports the getText( ), setText( ), getSelectedText( ), select( ), isEditable( ), and

setEditable( ) methods. In addition to these, TextArea adds the following

methods:

1. void append(String str) appends the string specified by str to

the end of the currenttext.

2. void insert(String str, int index) inserts the string passed in

strat the specified index

3. void replaceRange(String str, int startIndex, int endIndex)

replaces the characters from startIndex to endIndex1, withthe replacement text passed in str.

Using a TextArea

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Using a TextArea

Text areas only generate got-focus and lost-focus events.

Normally, your program simply obtains the current text when it is

needed. The following program creates a TextArea control

Using a TextArea

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Using a TextArea

Using a TextArea

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g

sample output


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Each Container object has a layout manager associated with it.

The layout manager is set by the setLayout( ) method

void setLayout(LayoutManager layoutObj)

layoutObj A reference to the desired layout manager

pass null for layoutObj If you wish to disable thelayout manager.

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FlowLayout

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y

FlowLayout is the default layout manager.

Components are laid out from the upper-left corner, left to

right and top to bottom.

Constructors for FlowLayout

1. FlowLayout( )

2. FlowLayout(int how)

3. FlowLayout(int how, int horz, int vert)

FlowLayout

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y


1. The first form creates the default layout, which centerscomponents and leaves five pixels of space between each

component

2. The second form lets you specify how each line is aligned.

Valid values forhow are as follows:

1. FlowLayout.LEFT

2. FlowLayout.CENTER

3. FlowLayout.RIGHT

4. FlowLayout.LEADING

5. FlowLayout.TRAILING

FlowLayout

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y


3. The third form allows you to specify the horizontal and

vertical space left between components

Here is a version of the CheckboxDemo applet( the controls are left aligned )

FlowLayout

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FlowLayout

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FlowLayout

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FlowLayout

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sample output

BorderLayout

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The BorderLayout class implements a common layout

style for top-level windows.

It has four narrow, fixed-width components at the

edges and one large area in the center.

The four sides are referred to as north, south, east, and

west. The middle area is called the center.

BorderLayout

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Constructors defined by BorderLayout

1. BorderLayout( ) Creates a default border layout.

2. BorderLayout(int horz, int vert)

Allows you to specify the horizontal and vertical

space left between components in horzand vert

BorderLayout defines the following constants that specify the

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BorderLayout defines the following constants that specify the

regions:

BorderLayout.CENTER

BorderLayout.SOUTH

BorderLayout.EAST

BorderLayout.WEST

BorderLayout.NORTH

Use these constants with the following form of add( ), which is

defined by Container:

void add(Component compObj, Object region);

region specifies where the componentwill be added.

Here is an example of a BorderLayout with a component in each

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Here is an example of a BorderLayout with a component in each

layout area

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Sample output

Using Insets

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To leave a small amount of space between the container that

holds your components and the window that contains it. To

do this :

Override the getInsets( ) method that is defined by Container

Insets getInsets( )

returns an Insets object that containsthe top, bottom, left, and right inset

Constructor for Insets

Insets(int top, int left, int bottom, int right)

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Using Insets

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Using Insets

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Output from the InsetsDemo applet

GridLayout

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GridLayout lays out components in a two-dimensional grid.

The constructors supported

1. GridLayout( ) creates a single-column grid layout

2. GridLayout(int numRows, int numColumns )

3. GridLayout(int numRows, int numColumns, int horz, int vert)

The third form allows you to specify the horizontal and vertical

space left between components in horz andvert, respectively.

numRow , numColumns specified number of rows and columns

GridLayout

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Here is a sample program that creates a 44 grid and fills it in with

15 buttons, each labeled with its index:

GridLayout

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GridLayout

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the output generated by the GridLayoutDemo applet:

CardLayout

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It stores several different layouts

Each layout can be thought of as being on a separate

index card in a deck

The deck can be shuffled so that any card is on top at a

given time

useful for user interfaces with optional components

that can be dynamically enabled and disabled upon user

input

CardLayout

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Provides these two constructors

1. CardLayout( )

2. CardLayout(int horz, int vert)

The first form creates a default card layout

The second form allows you to specify the horizontal

and vertical space left between components in horz and

vert, respectively

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d

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Menu Bars and Menus

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Steps to create Menus

1 first create an instance of MenuBar

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1. first create an instance ofMenuBar

2. Next, create instances of Menu that will define the selections

displayed on the bar

constructors for Menu:

1. Menu( )2. Menu(String optionName)3. Menu(String optionName, boolean removable)

optionName

specifies the name of the menu selection.removable If removable is true, the pop-up menu can be

removed and allowed to float free.

Steps to create Menus

To cretate menu items use MenuItems constructors :

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To cretate menu items use MenuItems constructors :

1. MenuItem( )

2. MenuItem(String itemName)

3. MenuItem(String itemName, MenuShortcut keyAccel)

itemNamethe name shown in the menu,

keyAccel is the menu shortcut forthis item.

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CheckboxMenuItem

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You can create a checkable menu item by using a subclass

ofMenuItem called CheckboxMenuItem

1. CheckboxMenuItem( )

2. CheckboxMenuItem(String itemName)

3. CheckboxMenuItem(String itemName, boolean on)

itemName the name shown in the menu

on ifon is true, the checkable entry is initially checked.

CheckboxMenuItem

You can obtain the status of a checkable item by calling

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You can obtain the status of a checkable item by calling

getState( ).

You can set it to a known state by using setState( ).

boolean getState( ) returns true if checked. Otherwise, it

returns false

void setState(boolean checked) checked must be TRUE

to check an item

Adding Menu item and Menu Bar

Add the item to a Menu object by using add( )

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Add the item to a Menu object byusing add( ),

MenuItem add(MenuItem item)

Item the item being added. The item is returned.

Once you have added all items to a Menu object, you can add that

object to the menu bar by using this version of add( ) defined by

MenuBar:

Menu add(Menu menu)

menu the menu being added. The menu is returned

Handling Menus

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Menus only generate events when an item of type MenuItem or

CheckboxMenuItem is selected.

Each time a menu item is selected, an ActionEvent object is

generated.

Each time a check box menu item is checked or unchecked, an

ItemEvent object is generated

Thus, you must implement the ActionListener and ItemListener

interfaces in order to handle these menu events.

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Dialog Boxes

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Dialog Boxes

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Dialog boxes are of type Dialog.

Two commonly used constructors :

1. Dialog(Frame parentWindow, boolean mode)

2. Dialog(Frame parentWindow, String title, boolean mode)

parentWindow the owner of the dialog box.

mode If mode is true, the dialog box is modal

title title of the dialog box

Generally, you will subclass Dialog, adding the functionality

required by your application

Dialog Boxes

Following is a modified version of the preceding menu program

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Following is a modified version of the preceding menu program

that displays a modeless dialog box when the New option ischosen.

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FileDialog

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To create a file dialog box, instantiate an object of type

FileDialog.

This causes a file dialog box to be displayed.

FileDialog provides these constructors:

1. FileDialog(Frame parent, String boxName)

2. FileDialog(Frame parent, String boxName, int how)

3. FileDialog(Frame parent)

FileDialog

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parent the owner of the dialog box,

boxName the name displayed in the boxs title bar.

If boxName is omitted, the title of the dialog box is empty.

how if FileDialog.LOAD, then the box is selecting a file for

reading.

If how is FileDialog.SAVE, the box is selecting a file for writing

FileDialog

FileDialog( ) id th f ll i th d

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FileDialog( ) provides the following methods

1. String getDirectory( )

2. String getFile( )

These methods return the directory and the filename, respectively.

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The output generated by this program

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The output generated by this program

awt-part2

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