Introduction to Abstract Window Toolkit (AWT) in Java


Abstract Window Toolkit(AWT) is an to create GUI using JAVA for Window based applications.It is said to be platform dependent as it implements itself over the underlying Operating System.Thus,it uses the native components like the windows,panels,dialog and whatever you see on the GUI of your Operating System.It calls the platforms subroutines to implement the functionalities.Depending on the Operating System(platform)the UI will be different from OS to OS.For Example you can see below that the same program rendered different UI on different platforms .

We have covered the basics by building a form UI using Abstract Window Toolkit (AWT) in Java.

On Windows XP

awtwindows

On Ubuntu 18.04

ubuntuawt2-1

If you'd see above images the look and feel of both of them is entirely like the native application and depends on the platform it is being run.

Structure

Lets get into the structure of the AWT.

awt_hierarchy

If you'd see the images shown previously (Windows XP and Ubuntu) on observing closely you will notice that there exists a conatainer(which has the close,maximize and minimize button on top-right) that is composed of several elements like buttons,text-box etc.These elements are called components.Container can be defined as a special type of component that is superset of all the other constituting components.As shown in the figure above Button,Label,Checkbox,Choice,Scrollbar are also the components.We won't go much into theoretical concepts instead we will focus on understanding the functionality and practical implementation of AWT.
Lets get ourselves familiar with some special containers that we would be using in future

  • Window: It implements a top level window container for GUI implmentation and has no borders or menubar.
  • Panel: It is used for holding other components and does not have any title bar, menu bar or border.
  • Frame: It is sub-window component which contains other elemental components like title bar,textfield,button,label etc.

Some basic functions/attributes:

Before moving on to develop a frame we should learn about some basic functions/methods and attributes that we would utilize to develop our GUI.

Let obj be an identifier for a component object.
  • obj.setBounds(int x-coordinate,int y-coordinate,int width ,int height)

Usage: Used to set components position on screen and its dimensions

Example:

//Creating a button component
 Button bt=new Button("Click Me"); 
        
// setting button position and dimension on screen
bt.setBounds(50,50,50,50);  
  • obj.setSize(int width,int height)

Usage: Used to set frame dimensions.
Example:

//Creating a new frame
Frame fr=new Frame("My Frame");
//Setting frame dimensions
fr.setSize(400, 400);  
  • obj.setVisible(boolean arg);

Usage: used to set the component visible(arg=true) i.e render the component on screen or to hide the component(arg=false).

Example:

import java.awt.*;  
public class example extends Frame{ 

//Constructor that accepts title for frame
example(String frame_title){ 

    //Instantiating a frame using frame class
    Frame fr=new Frame(frame_title);
    
    //Setting frame Dimensions
    fr.setSize(500, 300); 
    
    //Making frame visible
    fr.setVisible(true); 
}
public static void main(String args[])
   {
       //creating a frame and passing a title
       example fr = new example("Example Frame"); //String frame_tile="Example Frame"
   }
}  

Output on Ubuntu 18.04
framexample

  • obj.add(Object component);

Usage: used to add a component to another component.The component being added becomes a sub-component and the one to which it is being added becomes the parent container for this component.

Example:

import java.awt.*;
public class example extends Frame{

    //Constructor that takes Frame Title as arguement
    example(String frame_title){  
        
        //Instantiating a frame
        Frame fr=new Frame(frame_title);
        
        //Setting Frame width and height
        fr.setSize(500,300); 
        
        //Instantiating a Button
        Button bt=new Button("Click Me"); 
        
        // setting button position on screen
        bt.setBounds(100,50,100,50);  
        
        //adding button into frame 
        fr.add(bt); 
        
        //Setting no Layouts
        fr.setLayout(null);
        
       //Making the Frame Visible
        fr.setVisible(true);  
    }  
    public static void main(String args[]){  
         // Creating the instance of Frame
         example frame = new example("A Frame with Button");  
    }
}

Output on Ubnutu 18.04
Output-on-Ubuntu

To understand more we'll see an example!!

Example: A registration Form

Suppose we want to create a registration form and handle the input as well.

Our final output would be something similar to this:

awtdemo

Also here we would require an Event Listener that would keep track of our input and submit actions.We will use ActionListenerfor that.

So let's dive into the code. The explanations wherever neccessary have been added into the code itself using comments.

//Registration Form using AWT
/*To Compile: javac awt.java
     To run:  java Main
*/

import java.awt.*;
import java.awt.event.*;
public class registration_form implements ActionListener{

	TextField t = new TextField();

	TextField t1 = new TextField();

	Choice c = new Choice();

	Label submit = new Label("Registration Successful");

	Frame f = new Frame();

	MenuBar mb = new MenuBar();

	Menu m = new Menu("Menu");

	Label l = new Label("Name");

	Label l1 = new Label("Pasword: ");

	Label l2 = new Label("Occupation");

	Button s = new Button("Submit");

	Button clr = new Button("Clear");

	//Constructor that will create the form
	registration_form(){

		//Frame Layout
		f.setSize(600,600);
		f.setVisible(true);
		f.setLayout(null);
		f.setTitle("Registration Form");
		//End of Layout

		//Menu
		m.add("File");
		m.add("Edit");
		mb.add(m);
		f.setMenuBar(mb);
		//End of Menu


		//First Row : Name and TextField for name
		l.setBounds(50,100, 100,30);
		f.add(l);
		t.setBounds(170,100, 100,30);
		f.add(t);
		//End of row 1

		//row 2
		l1.setBounds(50,170, 100,30);
		//We'll display * for every char entered in password field
		t1.setEchoChar('*');	
		t1.setBounds(170,170, 100,30);
		f.add(l1);
		f.add(t1);
		//End of row 2

		//Choice Row 3
		l2.setBounds(50,220, 100,30);
		c.add("Student");
		c.add("Employee");
		c.add("Business");

		c.setBounds(170,220, 100,30);
		f.add(l2);
		f.add(c);
		//End of Choice row

		s.setBounds(50,280, 100,30);

		// We will add  functionality to the button
		s.addActionListener(this);
		
		clr.setBounds(170,280,100,30);		
		clr.addActionListener(this);
		
		f.add(s);
		f.add(clr);
		
		submit.setBounds(50,330, 300,30);
		
		f.add(submit);
		
		submit.setVisible(false);
	}

	//Handles events
	public void actionPerformed(ActionEvent e){

		//If Submit Button Pressed
		if (e.getSource() == s){	
		submit.setVisible(true);
		submit.setText("Name ="+t.getText() +" Occupation ="+c.getSelectedItem());
		}
		//If Clear Button Pressed
		else{	
			//Incase of exception			
			t.setText(" ");		
			t.setText("");
			t1.setText(" ");
			t1.setText("");

			//Selects the first option of choice on clearing screen
			c.select(0);		/
			submit.setVisible(false);
		}
	}
}

class Main{
    public static void main(String Z[]){
        registration_form reg = new registration_form();
    }
}
  • Source File name: registration_form.java
  • Compile using javac registration_form.java
  • Generated files(on compilation): registration_form.class and Main.class
  • Run using java Main

Conclusion

As AWT implements its GUI using the underlying Operating system,it's components become quite heavy.For example if you are creating a Button in AWT then you are actually asking OS to create a Button for you.Swing is another API that is popularly used because it is platform independent and light weight as well.The UI is independent of the Operating System.Not only is it lightweight but also it is more flexible and powerful.It offers advance features and components as well like lists,tables,combo box,slider etc.Thus,Swing has replaced AWT at most of the applications and uses.Nevertheless,AWT still finds its place where the look and feel of a native appliacation is concerned.

With this article at OpenGenus, you must have a good idea of using Abstract Window Toolkit (AWT) in Java by building a basic form. Enjoy.