Managing Scroll Bars

·         Scroll bars are used to select continuous values between a specified minimum and maximum  

·         It may be oriented horizontally or vertically.  

·         Scrollbar defines the following constructors:

Scrollbar( ) :creates a vertical scroll bar

Scrollbar(int style)  

If style is Scrollbar.VERTICAL, a vertical scroll bar is created.

If style is Scrollbar.HORIZONTAL, the scroll bar is horizontal.

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

the initial value of the scroll bar is passed in initialValue.

The minimum and maximum values for the scroll bar are specified by min and max

The number of units represented by the height of the thumb is passed in thumbSize.   

·         current value of the scroll bar, call getValue( ). 

·         To set the current value, call setValue( ).

Using a TextField  

·         implements a single-line text-entry area 

·         TextField is a subclass of TextComponent 

·         TextField defines the following constructors:

TextField( )                              : creates a default text field

TextField(int numChars)         : creates a text field that is numChars characters     wide

TextField(String str)                :initializes the text field with the string

 TextField(String str, int numChars): both the above 2 

Functions

getText( ), setText( ), getSelectedText( )

select(int startIndex, int endIndex)

boolean isEditable( ) returns true if the text may be changed

void setEditable(boolean canEdit):if canEdit is true, the text may be changed.

Handling a TextField

import java.awt.*;

import java.awt.event.*;

import java.applet.*;

/*<applet code="TextFieldDemo" width=300 height=180>

</applet > */

public class TextFieldDemo extends Applet implements ActionListener {

 TextField name, pass;

public void init() {

Label namep = new Label("Name: ", Label.RIGHT);

Label passp = new Label("Password: ", Label.RIGHT);

name = new TextField(12);

pass = new TextField(8);

pass.setEchoChar('?');

 add(namep); add(name); add(passp); add(pass);

 

// register to receive action events name.addActionListener(this); pass.addActionListener(this);

}

// User pressed Enter.

public void actionPerformed(ActionEvent ae) {

 repaint();

}

 public void paint(Graphics g)

 {

g.drawString("Name: " + name.getText(), 6, 60); g.drawString("Selected text in name: " + name.getSelectedText(), 6, 80);

g.drawString("Password: " + pass.getText(), 6, 100);

}

}

 

Using a TextArea 

·         AWT includes a simple multiline editor called TextArea 

·         Following are the constructors for TextArea:

TextArea( )

TextArea(int numLines, int numChars)

TextArea(String str)

TextArea(String str, int numLines, int numChars)

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

numLines specifies the height, in lines

numChars specifies its width

Initial text can becan specify the scroll bars by

SCROLLBARS_BOTH, SCROLLBARS_HORIZONTAL_ONLY, SCROLLBARS_NONE

·         void append(String str) void insert(String str, int index)

·          void replaceRange(String str, int startIndex, int endIndex)

 

Layout Managers  

·         All of the components are positioned by the default layout manager 

·         a layout manager automatically arranges your controls within a window by using some type of algorithm 

·         Each Container object has a layout manager associated with it 

·         The layout manager is set by the setLayout( ) method

 

FlowLayout 

·         FlowLayout is the default layout manager 

·         FlowLayout implements a simple layout style, which is similar to how words flow in a text editor 

·         by default, is left to right, top to bottom. 

·         the constructors for FlowLayout:

FlowLayout( )

centers components and leaves five pixels of space between each component

 FlowLayout(int how)

specify how each line is aligned.

                              Valid values for how are as follows:

o   FlowLayout.LEFT

o   FlowLayout.CENTER

o   FlowLayout.RIGHT

o    FlowLayout.LEADING

o   FlowLayout.TRAILING

 FlowLayout(int how, int horz, int vert)

allows us to specify the horizontal and vertical space left between components

 

BorderLayout 

    ·         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, & west. 

    ·         The middle area is called the center

GridLayout 

        ·         GridLayout lays out components in a 2D grid

        ·         When we instantiate a GridLayout, we define the number of rows and columns.

CardLayout 

    ·         it stores several different layouts 

    ·         The cards are typically held in an object of type Panel 

    ·         This panel must have CardLayout selected as its layout manager.

Menu Bars and Menus

         ·         A top-level window can have a menu bar associated with it

         ·         A menu bar displays a list of top-level menu choices. 

         ·         Each choice is associated with a drop-down menu

         ·         implemented in the AWT by the following classes:

o   MenuBar, Menu, and    

·         a menu bar contains one or more Menu objects  

·         Each Menu object contains a list of MenuItem objects 

·         Each MenuItem object represents something that can be selected by the user 

·         It is also possible to include checkable menu items

    oThese are menu options of type CheckboxMenuItem and will have a check mark next to them when they are selected

·                            constructors for Menu:

o   Menu( ) throws HeadlessException

o   Menu(String optionName) throws HeadlessException

optionName specifies the name of the menu selection.

o    Menu(String optionName, boolean removable) throws HeadlessException

If removable is true, the menu can be removed and allowed to float free

Otherwise, it will remain attached to the menu bar.

·         Individual menu items are of type MenuItem.

·         It defines these constructors:

o   MenuItem( ) throws HeadlessException

o   MenuItem(String itemName) throws HeadlessException

itemName is the name shown in the menu

o   MenuItem(String itemName, MenuShortcut keyAccel) throws HeadlessException

keyAccel is the menu shortcut for this item

Methods

Method	Description
setEnabled( )	can disable or enable a menu item
isEnabled( )	determines an item’s status
setLabel( )	change the name of a menu item
getLabel( )	retrieve the current name of the menu item