11.1 Introduction

Java’s big trump card is its Abstract window toolkit (AWT). It is an object oriented graphical user Interface(GUI) framework that allows you to design modern, accessible, graphical application interface. But Java’s AWT lets you design and implement GUIs that run unmodified on PC’s running any OS.

11.2 AWT

AWT has the flexibility that we can easily interface that appears the same on all platforms. The concept of Swing is also introduced. As of now Swing has taken over. JavaFX is also getting popular

11.3 AWT Package

The AWT classes are contained in the java.awt package which is  Java’s largest packages. It is hierarchical and is easy to understand and use.

11.3.1 AWT Components

java.awt contains  classes for creating user interfaces and for painting graphics and images. Any object on user interface like text box, label or button are called components which cause an event when a user interacts. For example when a mouse is clicked or when a button is pressed. The AWTEvent class and its subclasses are used to handle such events. The Component class is the root of all AWT components.

11.3.2 AWT container

A container is a component that can contain components and other containers. A container can also have a layout manager that controls the visual placement of components in the container. The AWT package contains several layout manager classes and an interface for building our own layout manager.

//loginAWT.java
import java.awt.*; 
class loginAWT {
loginAWT() {
Frame f = new Frame(); // create Frame
Label l1 = new Label("login name"); 
Label l2= new Label("Password");
TextField t1 = new TextField(); // create login TextField 
TextField t2= new TextField(); // Create password Textfield
Button b = new Button("Go"); // create a Button
// Set bounds for positioning l,b,t in f 
l1.setBounds(20, 80, 80, 30); 
l2.setBounds(20, 110,80,30);
t1.setBounds(100, 80, 80, 30); 
t2.setBounds(100,110,80,30);
b.setBounds(180, 100, 80, 30);
// add components to frame 
f.add(b); 
f.add(l1); 
f.add(t1); 
f.add(l2); 
f.add(t2);
// frame size and title 
f.setSize(400,300);
f.setTitle("login page"); 
f.setLayout(null); 
f.setVisible(true); 
}
// main method 
public static void main(String args[]) {
// creating instance of Frame class 
loginAWT login = new loginAWT();
}
}

11.5 The Delegation Event Model

This model is a modern approach for handling events which defines a standard and consistent mechanism to generate and process events. The concept involved in this model is quite simple: a source generates event and sends it to one or more listeners. In this scheme, listener simply waits until receives an event. Once received, the listener processes the event and then returns. In this model listeners.

The Delegation Event Model consists of four main components:

1. the event source,
2. the event object,
3. the event listener, and
4. the event handler.

The event source is the object that generates the event. The event object contains information about the event. The event listener is the object that is notified when the event occurs. The event handler is the object that handles the event.

In this model listeners must register with a source in order to receive an event notification.

11.6 Event

In delegation model, an event is an object that describers a state change in a source. Examples for events in user interfacing environments are pressing a button, entering a character via keyboard, selecting a menu item in a list and clicking the mouse. Some other examples of events are a counter exceeding the value, a software or hardware failure occurs or an operation is completed.

11.6.1 Event Sources

A source is an object that generates an event. Sources may generate more than one type of event. A source must register listeners in order for the listeners to receive notifications about a specific type of event. See figure 11.3.

The general form of registration of each type of event is:

public void addTypeListener(TypeListener el)

Here Type is the name of the event and el is a reference to the event listener. For example, The method that registers a mouse motion listener is called addMouseMotionListener().

11.6.2 Event Listeners

A listener is an object that is notified when an event occurs. It has two major requirements.

1. It must have registered with one or more sources to receive notifications about specific type of events
2. It must implement methods to receive and process these notifications.

The methods that receive and process events are defined in a set of interfaces found in java.awt.event.

11.6.3 Event Classes

The classes that represent events are at the core of Java’s event handling mechanism. At the root of the Java event class hierarchy is EventObject, which is in java.util. It is the superclass for all events. Its one constructor is shown as below

EventObject(Object src)

Here, src is the object that generates this event.

EventObject contains two methods: getSource() and toString(). The getSource() method returns the source of the event. It is of the form shown below

Object getSource()

The toString() returns the string equivalent of the event.

The AWTEvent, defined within the java.awt package, is a subclass of EventObject. It is the superclass of all AWT-based events used by the delegation event model.

The package java.awt.event defines several types of events that are generated by various user interface elements.

11.6.4 Sources of Events

The sources for all the events stated above are some user interface components. Some of these components along with their description(i.e how they generate an event) is given in the below table.

11.6.5 Event Listener Interfaces

When an event is generated by the event sources (Stated in the above table) then the event processing is left to the listener registered by the source, the event listener is responsible for the processing and returning results to the source. For example when a button pressed or an item in the list is double clicked or a menu item is selected(all these events are the examples of the action events) then ActionListener is activated to take respective action for the source that generates event. Similarly for each event there are corresponding listeners that are explained in the below table.

The AWT defines windows according to a class hierarchy that adds functionality and specificity with each level The two most common windows are those derived from panel, which is used by applets, and those derived from frame, which creates a standard window. Much of the functionality of these windows are derived from their parent classes. Thus the description of the AWT hierarchy of the classes is shown below.

All the elements like the button, text fields, scroll bars, etc. are called components.  Every component is added to a container.

After setting all the layouts of the windows for an applet, we can add some AWT tools(components for the container) by using add function. Every container has its own layout manager(that is, layout style). Individual components are grouped together in containers. The classes that extend Container class are known as container. Examples are  window,Frame, Dialog and Panel

11.7 Discussion about the AWT classes

11.7.1 TextField

TextField is just a box that can hold text. These are also known as text boxes and edit controls. Textfields are declared as

TextField t1;

After creating t1 as TextField we can create a new text field for t1 by using a constructor as shown below

T1=new TextField(); or

T1=new TextField(String);

String may be a caption or some text to be displayed in that text field.

Some of Java TextField class methods are given below.

11.7.2 Button

This is an important tool in user interface environment. Buttons are also known as control. Buttons because based on the event occurred on the Button the control may be changed. Buttons are declared as below

Button b;

Above declaration b as a button and is created before adding ot to applet and is done by using a constructor as shown below

b=newButton(); or

b=newButton(String);

String is the label for the button.

Some of Java Button class methods are given below.

11.7.3 TextArea

Handling text area is similar to text field the only difference is that text are contains several lines of text where as we have only one line in text field. The methods for text area are almost similar to text fields. Text areas are declared as

TextArea t;

Above declaration only declares t as TextArea and is constructed by using the constructors shown below

T=new TextArea() or

T=new TextArea(int, int)

Int, int represents the number of rows and columns of the text area.

Some of Java TextArea Class methods

Some methods of TextField also applicable to TextArea.

11.7.4 Label

Label control is a control element whose function is to display a text and nothing more. Labels are declared as following

Label l;

Here 1 is declared as a label and is created by using constructors which are of form shown below.

l=new label(); or

l=new label(String);

String is the text to be displayed as label.

Some of Java label class methods

The following program creates a frame with name “first AWT program”  and then adds a label “hi from AWT”, then a text box is added which is initially empty, a button with text “click here” and when the button is clicked with mouse the text box is set to “Button clicked”.

Program 11.2 Program to demonstrate AWT listeners

//firstAWT.java
//Click here for code
import java.awt.*;

import java.awt.event.*;

public class firstAWT

{
public static void main(String args[])
{


Frame f = new Frame("first AWT program"); 
f.setSize(300,300);
f.setVisible(true);

TextField t=new TextField();
t.setBounds(80,80,80,80);
f.add(t);
Button b=new Button("Click here");
b.setBounds(160,160,100,80);
f.add(b);
Label l=new Label("hi from AWT");
f.add(l);
b.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{

if(e.getSource()==b) t.setText("Button clicked");

}
}

);

}
}

11.7.5 Check Boxes

It is a control that is used to turn an option on or off. It contains of small box that can either contains a check mark or not. There is a label associated with each check box that describers what option the box represents. You change the state of the check box by clicking on it.

Checkbox can be declared as follows

Checkbox c;

Here c is declared as a checkbox and is created by using the constructors as follows

C=new Checkbox() or

c-new Checkbox(String, Boolean)

Some of Java Checkbox Class methods

11.7.6 CheckboxGroup

Radio buttons are similar to check boxes, the only difference is that we can select only one button at time but not more that one as in check boxes. We can add radio buttons to a group by using CheckboxGroup object Suppose we want to create two radio buttons r1,r2. We first declare a checkbox group in that we add the two check boxes named r1,r2 as below

CheckboxGroup c;

Checkbox r1,r2;

Above are declaration and the construction is as follows

C=new CheckboxGroup();

R1=new checkbox(“first”, false, c);

R2=new Checkbox(“second:, false, c);

Some of Java CheckboxGroup class methods

11.7.7 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 that you can click to move the current value of the scroll bar one unit in the direction if the arrow.

Scrollbars are declared as follows

Scrollbar s;

Here s is declared as a scrollbar and is created by using one of the constructors of scrollbar class as below.

s=new scrollbar(); or

s=new scrollbar(int);

int is the orientation of the scroll bar.

Some of java Scrollbar class methods

Similarly we have setMaximum(int), setMinimum(int), setValue(int), setOrientation(int), setVisibleAmount(int), setUnitIncrement(int)…etc. to set the dimensions of the scroll bar.

Scroll pane is a plane which contains scroll bars around the edges of this container as needed. These scroll pane are declared as follows.

ScrollPane sp;

Here sp is declared as scroll pane and is constructed as below

sp=new scrollPane() or

sp=new ScrollOane(int)

11.7.8 Choice Controls

The choice control is just the drop-down list box which is very familiar in windows environment. This choice class is used to create a pop-up list of items from which the user may choose. When inactive, a choice component takes up only enough space to show the currently selected item. When the user clicks n it, the whole list of choices pops up, and new selection can be made.

Choice lists are declared as follows

Choice c;

Here c is declared as choicebox and is created by sing one of the constructors of the choice list class as below.

c=new Choice();

Some of java choice list class methods

Program 11.3 Construct UI that contains a choice box and text box such that the item selected in choice box is to be displayed in the text box.

//constructUI.java 
//importing awt class 
import java.awt.*; 
import java.awt.event.*; 
public class choiceAWT implements ItemListener { 
TextField t; Choice c;
// class constructor 
choiceAWT() { 

// creating a frame 
Frame f = new Frame(); 
Label l=new Label("SELECT CITY"); 
t=new TextField(); 

// creating a choice component 
c = new Choice(); 

// setting the bounds of choice menu 
c.setBounds(100, 100, 100, 75); 
t.setBounds(100,150,100,75); 
l.setBounds(100,50,100,75);

// adding items to the choice menu 
c.add("Hyderabad"); 
c.add("Guntur"); 
c.add("Vizag"); 
c.add("Vijayawada"); 
c.add("Tirupathi"); 

// adding choice menu to frame 
f.add(c); 
f.add(t); 
f.add(l); 

// setting size, layout and visibility of frame 
f.setSize(500, 500); 
f.setLayout(null); 
f.setVisible(true); 
c.addItemListener(this); 
}
public void itemStateChanged(ItemEvent e) { 
if(e.getItemSelectable()==c)
t.setText(c.getSelectedItem());
}

// main method 
public static void main(String args[]) 
{ 
new choiceAWT(); 
} 
}

11.7.9 ScrollLists

A scrolling list presents choices that the user may select from using the up and down arrows that appear at right in the list control. The scroll list object can be declared as follows

List l;

Here l is a list and is created by using any one of the constructors of the List class which is of the form shown below

L= new List() or

L=new List(int)

int is the number of visible lines in the list.

Some of Java list class methods

Program 11.4.  Program to implement scroll list

//listAWT.java
import java.awt.*;
import java.awt.event.*;
public class listAWT implements ItemListener {
List l;
TextField t;

listAWT()
{

Frame f = new Frame();
Label lb=new Label("CLICK ON A BOOK");

t=new TextField();

l=new List();
l.setBounds(100, 150, 200, 75); 
t.setBounds(100,230,200,75); 
lb.setBounds(100,50,150,75);
l.add("Java Programming ");
l.add(" C Programming ");
l.add("C++ Programming ");
l.add("Windows Programming ");
l.add("Shell Programming ");
l.add(" Programming with VC++");
l.add(" Programming VB");


f.add(l);
f.add(t);
f.add(lb);

f.setSize(500, 500); 
f.setLayout(null); 
f.setVisible(true); 
l.addItemListener(this);

}

public void itemStateChanged(ItemEvent e)
{
if(e.getItemSelectable()==l)
t.setText(l.getSelectedItem());
}

// main method 
public static void main(String args[]) 
{ 
new listAWT(); 
} 

}

11.8 Windows

The AWT defines according to class hierarchy that adds functionality and specificity with each level. The two most common windows are those derived from panel, which is used by applets, and those derived from Frame, which creates a standard window.

A window object is declared as

Demoframe w1;

Some of the frame class methods:

Program 11.5 Frame Layout demonstration

//demoFrame.java

import java.awt.*;
import java.awt.event.*;
import java.awt.GridLayout.*;
public class demoFrame implements ActionListener
{
TextField t;
Button c;
demoFrame()
{
Frame f=new Frame();
f.setLayout(new GridLayout(2,1));
t=new TextField(10);
f.add(t);
c=new Button("click here");
f.add(c);
c.setBounds(100, 150, 200, 75); 
t.setBounds(100,230,200,75);

f.setSize(500, 500); 
f.setLayout(null); 
f.setVisible(true);

c.addActionListener(this);
}

public void actionPerformed(ActionEvent e)
{
if(e.getSource()==c) t.setText("clicked");
}

// main method 
public static void main(String args[]) 
{ 
new demoFrame(); 
}


}

Program 11.6 Program to implement ActionListener

//Save both windowAWT.java and demoFrame2.java in different files. Compile them and then run windowAWT class file.

//windowAWT.java

import java.awt.*;
import java.awt.event.*;
public class windowAWT implements ActionListener
{
Button b1,b2;
demoFrame w;
windowAWT()
{

Frame f1=new Frame();

b1=new Button("show");
b1.setBounds(100, 150, 200, 75);

f1.add(b1);

b1.addActionListener(this);
b1.addActionListener(this);
f1.add(b1);

b2=new Button("hide");
b2.setBounds(100,230,200,75); 
b2.addActionListener(this);

f1.add(b2);

w=new demoFrame2();
w.setSize(500,050);

f1.setSize(500, 500); 
f1.setLayout(null); 
f1.setVisible(true); 
}

public void actionPerformed(ActionEvent e)
{
if(e.getSource()==b1) w.setVisible(true);
if(e.getSource()==b2) w.setVisible(false);
}
// main method 
public static void main(String args[]) 
{ 
new windowAWT(); 
}

}

11.9 Menu bars

A menu bar displays a list of top level menu choices. Each choice is associated with a drop down menu.

Menu bar is declared as

MenuBar mbar= new MenuBar();

Menu is declared as

Menu mfile=Menu(“file”);

Some of the menu class methods are given below.

11.10 Graphics

The AWT supports a rich assortment of graphical methods. All graphics are drawn relative to window. The graphics class encapsulates a graphical context. The Graphics class defines a number of drawing functions. Each shape can be drawn edge-only or filled.

11.10.1 Drawing lines

Lines are drawn by means of the drawLine() method.

void drawLine(int startX, int startY, int endX, int endY);

11.10.2 Drawing Rectangle

Rectangle are drawn by using drawRect() and filled rectangles are drawn by sing fillRect() method

vdrawRondRect (int top, int left, int width, int height, int xDiam, int yDiam)

void fillRoundRect(int top, int left, int width, int height, int xDiam, int yDiam)

11.10.3 Drawing Ellipses and Circles

To draw an ellipse we use drawOval() and to fill an ellipse we use fillOval() are used.

void drawOval(int top, int left, int width, int height)

void fillOval(int top, int left, int width, int height)

11.10.4 Drawing Arcs

Arcs can be drawn with drawArc() and fillArc() methods.

void drawArc(int top, int left, int width, int height, int startangle, int sweepangel)

void fillArc(int top, int left, int width, int height, int startangle, int sweepangle)

11.10.5 Drawing Polygons

We can draw polygons by using drawPolygon() and fillPolygon().

void drawPolygon(int x[], int y[], int numpoint)

void fillPolygon(int x[], int y[], int numpoint)

In order to size a graphics object to fit in current window it is necessary to find the size of the current window. The size of window can be obtained by using getSize() method.

This method returns the dimensions of the current window encapsulated within a Dimension object.

11.10.6 Color Class

The color class defines several methods that help manipulates colors.

Using Hue, saturation, and Brightness: The hue-saturation-brightness(HSB) color model is an alternative to red-green-blue(RGB) for specifying particular colors. Figuratively, hue is a wheel of color. The hue is specified with a number between 0.0 and 1.0. Saturation is another scale ranging from 0.0 to 1.0, where 1 is bright white and 0 is black.

Color supplies two methods that convert between RGB and HSB.

Static int HSBtoRGB(float hue, float saturation, float brightness)

Static float[] RGBtoHSB(int red, int green, int blue, float values[])

We can obtain the red, green, and blue components of a color by using gerRed(), getBlue() and getGreen().

To obtain a packed, RGB representation of a color we use getRGB()

int getRGB()

We can change color by calling the graphics method setColor() and we can obtain the current color by getColor().

void setcolor(color newColor)

Color getColor()

11.10.7 Font

The AWT supports multiple type fonts. The AWT provides flexibility by abstracting font-manipulation operations and allowing for dynamic selection of fonts. Fonts are encapsulated by Font class.

Some of java Font class methods

Boolean isItalic(), Boolean isPlain() does  the same function similar to isBold() but in these cases test is made for italic and plain text in success.

11.11 Summary

In this chapter you have learned in detail about AWT package, the components, containers, panels, windows and Listeners.