PPT - Unit 1.1 - AWT Components.pdf

ADVANCED JAVA PROGRAMMING AJP UNIT – I AWT [ABSTRACT WINDOWING TOOLKIT] Sunil Prakashrao Emekar Lecturer in Computer Engg. Government Polytechnic Karad E-mail: [email protected] JAVA AWT (ABSTRACT WINDOWING TOOLKIT)  Java AWT (Ab...

ADVANCED JAVA PROGRAMMING AJP UNIT – I AWT [ABSTRACT WINDOWING TOOLKIT] Sunil Prakashrao Emekar Lecturer in Computer Engg. Government Polytechnic Karad E-mail: [email protected] JAVA AWT (ABSTRACT WINDOWING TOOLKIT)  Java AWT (Abstract Windowing Toolkit) is an API to develop GUI or window-based applications in java.  Java AWT components are platform-dependent i.e. components are displayed according to the view of operating system.  AWT is heavyweight i.e. its components are using the resources of OS.  The java.awt package provides classes for AWT api such as TextField, Label, TextArea, RadioButton, CheckBox, Choice, List etc.  AWT CLASSES  The AWT classes are contained in the java.awt package. It is one of Java’s largest packages.  it is logically organized in a top- down, hierarchical fashion.  The AWT defines windows according to a class hierarchy that adds functionality and specificity with each level. Container:  A container is responsible for laying out (that is, positioning) any components that it contains. It does this through the use of various layout managers.  The classes that extends Container class are known as container such as Frame, Dialog and Panel.  Window  The window is the container that have borders and menu bars. You wont create object of window directly.  You must use frame, dialog or another window for creating a window.  Panel  The Panel is the container that doesn't contain title bar and menu bars. (Superclass of Applet)  It can have other components like button, textfield etc.  Frame  It is a subclass of Window and has a title bar, menu bar, borders, and resizing corners.  It can have other components like button, textfield etc. USEFUL METHODS OF COMPONENT CLASS WORKING WITH FRAME WINDOWS  After the applet, the type of window you will most often create is derived from Frame.  You will use it to create child windows within applets, and top-level or child windows for applications.  Frame’s constructors:  Frame( )  Frame(String title)  Setting the Window’s Dimensions:  The setSize( ) method is used to set the dimensions of the window.  void setSize(int newWidth, int newHeight)  Hiding and Showing a Window  After a frame window has been created, it will not be visible until you call setVisible( ).  void setVisible(boolean visibleFlag)  The component is visible if the argument to this method is true. Otherwise, it is hidden.  Setting a Window’s Title  You can change the title in a frame window using setTitle( ),  void setTitle(String newTitle) import java.awt.*; class Test { public static void main(String args[]) { Frame f = new Frame(“Example"); f.setSize(400,400); f.setLayout(null); f.setVisible(true); } } import java.awt.*; import java.applet.*; public class LabelDemo extends Applet { public void init() { Frame f=new Frame(); f.setSize(300,300); f.setVisible(true); } } USING AWT CONTROLS, LAYOUT MANAGERS, AND MENUS  Controls are components that allow a user to interact with your application in various ways.  The AWT supports the following types of controls: Labels Push buttons Check boxes Choice lists Lists Scroll bars Text editing  These controls are subclasses of Component. ADDING AND REMOVING CONTROLS  To include a control in a window, you must add it to the window.  To do this, you must first create an instance of the desired control and then add it to a window by calling add( ), To include a control in a window, you must add it to the window.  To do this, first create an instance of the desired control and then add it to a window by calling add( ) Component add(Component compObj) compObj is an instance of the control that you want to add.  Sometimes you will want to remove a control from a window when the control is no longer needed. To do this, call remove( ). This method is also defined by Container.  It has this general form: void remove(Component obj) obj is a reference to the control you want to remove.  You can remove all controls by calling removeAll( ) LABELS  The easiest control to use is a label. A label is an object of type Label, and it contains a string, which it displays.  Labels are passive controls that do not support any interaction with the user.  Label defines the following constructors:  Label( )  Label(String str)  Label(String str, int how)  alignment specified by how. The value of how must be one of these three constants: Label.LEFT, Label.RIGHT, or Label.CENTER.  You can set or change the text in a label by using the setText( ) method.  You can obtain the current label by calling getText( ).  void setText(String str)  String getText( ) import java.awt.*; class LabelExample{ public static void main(String args[]){ Frame f= new Frame("Label Example"); Label l1,l2; l1=new Label("First Label."); l1.setBounds(50,100, 100,30); l2=new Label("Second Label."); l2.setBounds(50,150, 100,30); f.add(l1); f.add(l2); f.setSize(400,400); f.setLayout(null); f.setVisible(true); } } // Demonstrate Labels import java.awt.*; import java.applet.*; public class LabelDemo extends Applet { public void init() { Label one = new Label("One"); Label two = new Label("Two"); Label three = new Label("Three"); // add labels to applet window add(one); add(two); add(three); } } 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.  Button defines these two constructors:  Button( )  Button(String str) The first version creates an empty button. The second creates a button that contains str as a label.  After a button has been created, you can set its label by calling setLabel( ).  You can retrieve its label by calling getLabel( ). These methods are as follows:  void setLabel(String str)  String getLabel( ) EVENT AND LISTENER (JAVA EVENT HANDLING)  Changing the state of an object is known as an event. For example, click on button, dragging mouse etc.  The java.awt.event package provides many event classes and Listener interfaces for event handling.  Registration Methods  For registering the component with the Listener, many classes provide the registration methods. For example:  Button  public void addActionListener(ActionListener a){}  MenuItem  public void addActionListener(ActionListener a){}  TextField  public void addActionListener(ActionListener a){}  public void addTextListener(TextListener a){}  TextArea  public void addTextListener(TextListener a){}  Checkbox  public void addItemListener(ItemListener a){}  Choice  public void addItemListener(ItemListener a){}  List  public void addActionListener(ActionListener a){}  public void addItemListener(ItemListener a){} APPLYING CHECK BOXES  A check box is a control that is used to turn an option on or off.  Checkbox supports these constructors:  Checkbox( )  Checkbox(String str)  Checkbox(String str, boolean on)  Checkbox(String str, boolean on, CheckboxGroup cbGroup)  Checkbox(String str, CheckboxGroup cbGroup, boolean on).  Where  str-label  on - If on is true, the check box is initially checked; otherwise, it is cleared.  cbGroup - group is specified by cbGroup  To retrieve the current state of a check box, call getState( ).  boolean getState( )  To set its state, call setState( ).  void setState(boolean on)  You can obtain the current label associated with a check box by calling getLabel( ).  String getLabel( )  To set the label, call setLabel( ).  void setLabel(String str) CHECKBOXGROUP (RADIO BUTTON)  It is possible to create 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.  These check boxes are often called radio buttons.  Check box groups are objects of type CheckboxGroup. Only the default constructor is defined, which creates an empty group.  You can determine which check box in a group is currently selected by calling getSelectedCheckbox( ).  Checkbox getSelectedCheckbox( ) CHOICE CONTROLS  The Choice class is used to create a pop-up list of items from which the user may choose.  Choice only defines the default constructor, which creates an empty list. Choice()  To add a selection to the list, call add( ). It has this general form:  void add(String name)  Here, name is the name of the item being added. Items are added to the list in the order in which calls to add( ) occur.  To determine which item is currently selected, you may call either getSelectedItem( ) or getSelectedIndex( ).  String getSelectedItem( )  int getSelectedIndex( )  To obtain the number of items in the list, call getItemCount( ).  int getItemCount( )  You can set the currently selected item using the select( ) method with either a zero-based integer index or a string that will match a name in the list. These methods are shown here:  void select(int index)  void select(String name)  Given an index, you can obtain the name associated with the item at that index by calling getItem( ), which has this general form:  String getItem(int index) Here, index specifies the index of the desired item. TEXTFIELD  The TextField class implements a single-line text- entry area, usually called an edit control.  TextField is a subclass of TextComponent.  TextField defines the following constructors:  TextField( )  TextField(int numChars) :-creates a text field that is numChars characters wide.  TextField(String str) :- The third form initializes the text field with the string contained in str.  TextField(String str, int numChars) :- The fourth form initializes a text field and sets its width.  TextField (and its superclass TextComponent) provides several methods that allow you to utilize a text field.  To obtain the string currently contained in the text field, call getText( ).  String getText( )  To set the text, call setText( ).  void setText(String str) //Here, str is the new string.  You can determine editability by calling isEditable( ). These methods are shown here:  boolean isEditable( )  void setEditable(boolean canEdit) SETTING ECHO CHARECTER  You can disable the echoing of the characters as they are typed by calling setEchoChar( ).  void setEchoChar(char ch)  You can check a text field to see if it is in this mode with the echoCharIsSet( ) method.  boolean echoCharIsSet( )  You can retrieve the echo character by calling the getEchoChar( ) method.  char getEchoChar( )  Here, ch specifies the character to be echoed. USING LISTS  The List class provides a compact, multiple-choice, scrolling selection list.  List object can be constructed to show any number of choices in the visible window.  List( )  List(int numRows)  List(int numRows, boolean multipleSelect)  numRows specifies the number of entries in the list that will always be visible  To add a selection to the list, call add( ). It has the following two forms:  void add(String name)  void add(String name, int index)  For lists that allow only single selection  String getSelectedItem( )  int getSelectedIndex( )  For lists that allow multiple selection  String[ ] getSelectedItems( )  int[ ] getSelectedIndexes( )  The first item is at index 0. If more than one item is selected, or if no selection has yet been made, –1 is returned.  To obtain the number of items in the list.  int getItemCount( )  You can set the currently selected item by using the select( ) method with a zero-based integer index.  void select(int index)  Given an index, you can obtain the name associated  String getItem(int index) MANAGING SCROLL BARS  Scroll bars are used to select continuous values between a specified minimum and maximum.  Scroll bars may be oriented horizontally or vertically.  A scroll bar is actually a composite of several individual parts.(Each end has an arrow & slider box (or thumb)).  Scroll bars are encapsulated by the Scrollbar class.  Scrollbar( )  Scrollbar(int style)  void setValues(int initialValue, int thumbSize, int min, int max)  Scrollbar(int style, int initialValue, int thumbSize, int min, int max)  Where  If style is Scrollbar.VERTICAL, a vertical scrollbar is created. If style is Scrollbar.HORIZONTAL, the scroll bar is horizontal.  The minimum and maximum values for the scroll bar are specified by min and max  To obtain the current value of the scroll bar.  int getValue( )  To set the current value, call setValue( ).  void setValue(int newValue)  You can also retrieve the minimum and maximum values  int getMinimum( )  int getMaximum( )  Setting increment  void setUnitIncrement(int newIncr) //default 1  void setBlockIncrement(int newIncr) //default10 TEXTAREA  Sometimes a single line of text input is not enough for a given task.  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)  Where  numLines specifies the height, in lines, of the text area,  numChars specifies its width  Initial text can be specified by str.  sBars must be one of these values:  SCROLLBARS_BOTH  SCROLLBARS_NONE  SCROLLBARS_HORIZONTAL_ONLY  SCROLLBARS_VERTICAL_ONLY  TextArea is a subclass of TextComponent. Therefore, it supports the  getText( )  setText( )  getSelectedText( )  select( )  isEditable( )  setEditable( )  TextArea adds the following methods:  The append( ) method appends the string specified by str to the end of the current text.  void append(String str)  insert( ) inserts the string passed in str at the specified index.  void insert(String str, int index)  To replace text, call replaceRange( ). It replaces the characters from startIndex to endIndex–1, with the replacement text passed in str.  void replaceRange(String str, int startIndex, int endIndex).