Java - Swing custom components - Rounded JButton

Unlike AWT, Java Swing tool kit provides feasibilty to create custom components and containers.

To understand Java GUI toolkits more clearly, please read my other articles on Swing and AWT. 

In this article I focus more on building custom components.

Let us see how to create simple Rounded JButton. The below program demonstrates How rounded JButton can be created and added to a JFrame.

 

Program:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Shape;
import java.awt.geom.Ellipse2D;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class RoundedJButton extends JButton {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	public RoundedJButton(String title) {
		super(title);
		Dimension size = getPreferredSize();
		size.width = size.height = Math.max(size.width, size.height);
		setPreferredSize(size);

		setContentAreaFilled(false);
	}

	@Override
	protected void paintComponent(Graphics g) {
		if (getModel().isArmed()) {
			g.setColor(Color.lightGray);
		} else {
			g.setColor(getBackground());
		}
		g.fillOval(0, 0, getSize().width - 1, getSize().height - 1);

		super.paintComponent(g);
	}

	@Override
	protected void paintBorder(Graphics g) {
		g.setColor(getForeground());
		g.drawOval(0, 0, getSize().width - 1, getSize().height - 1);
	}

	Shape shape;

	@Override
	public boolean contains(int x, int y) {
		if (shape == null || !shape.getBounds().equals(getBounds())) {
			shape = new Ellipse2D.Float(0, 0, getWidth(), getHeight());
		}
		return shape.contains(x, y);
	}

	public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException {

		JFrame frame = new JFrame();
		frame.setTitle("It's all about Java...");
		frame.setSize(150, 150);
		GridLayout layout = new GridLayout();
		layout.setRows(1);
		layout.setHgap(10);
		layout.setVgap(10);
		frame.setLayout(layout);

		JTextField field1 = new JTextField();
		field1.setText("This is a textfield!");
		frame.getContentPane().add(field1);

		RoundedJButton button = new RoundedJButton("Browse");
		button.setBackground(Color.gray);
		button.setForeground(Color.GREEN);
		frame.getContentPane().add(button);

		UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

		SwingUtilities.invokeLater(new Runnable() {
			@Override
			public void run() {
				frame.pack();
				frame.setVisible(true);
			}
		});
	}
}

There are two parts in the program. First part creates RoundedJButton component by extending JButton. and second part creates JFrame and appends two components. 1. RoundedJButton and 2. JTextField

First Part:

RoundedJButton overrides paintComponent(Graphics g) and paintBorder(Graphics g) to get the circled shape to the Button. 

Second Part:

Second part contains main method which creates JFrame object and adds 2 components to JFrame dialog.

Also applies System look and feel by using following

UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

I will explain clearly about pluggable look and feels also known as PLAF in future articles.

That's all for now!

Happy coding... :) 

Exception handling and java keywords

Exception:

Exception in a programming language and in English language is pretty similar. Exception means being different from or not following the rules. And in programming language like Java, exception is  an event which occurs during the execution of a program that disturbs the complete flow of application or program.

When something beyond expected happens while executing a program is considered as an error. handling these errors or abnormality is called as Exception handling.

Exception Handling:

Exception handling in java is managed with the help of java keywords and java API support.. 

            1. Java Keywords

            2. Java API support

Java Keywords: 

There are 5 keywords in Java.

          1. Try

          2. catch

          3. finally

          4. throw

   and 5. throws

These five keywords used all together or combination of few keywords are used on need basis.

1. Try:

The code or set of instructions which are prone to errors or exceptions are enclosed in try block.

For example dividing a five or some number with zero [5/0]. The result of 5/0 is undefined and in Java,  this scenario is considered as exception.

2. Catch:

Usually try block is followed by a catch block. If some exception is occurred in try block, the execution control is moved to catch block instead of  continuing the execution of  try block's code. 

The purpose of catch block is, handling the exceptions that are raised in try.

There is a possibility of handling multiple scenarios in multiple catches. 

NOTE: Multiple catches can be written for single try.

Java code example:

           try{

                   ---                     // code

                } catch(OtherException e) {

                   ---                    // code

               }catch(AnotherException e) {

                }      

3. Finally:

Usually if there is an exception in try block, the rest of the lines in try are not executed and control moves on to catch block. And if there is no exception at all in try block control never moves to catch block. Then catch block is considered to be dead code. 

Then where must we write mandatory code? 

So, finally block is written after try and catch which gets executed always. 

Java code example:

            try{

                  ---

                } catch (Exception e) {

                  ---

                } finally{

                  ---              // mandatory code for execution

                } 

NOTE: Always put mandatory code in finally block. For example: closing IO resources connections like network and database connections etc

4. Throws and Throw:

Throws and throw keywords works along with Java API support. I will explain the Java API support for Exception handling in next subsequent articles. 

For now, we can understand that for every exception scenario there is one Java class(Java API). Example: Number divided by zero. [5/0]. The result is ArithmeticException

Java code example:

     try{

               int result = 5/0;

                ---        // other code

         }catch(ArithmeticException e) {

                ---        // exception of try block is handled here   

         }  

  Why there is no "throws" keyword here....?

The alternative solution for above snippet with throws and throw for checking election voting age eligibility exception is:

void votingAgeNumber() throws ArithmeticException{

                int age = 12; 

                if(age <=18) {

                           throw new ArithmeticException("Age is not sufficient to vote");

                 }

                 ---       // other code              

           }

NOTE: Sometimes "throws" keyword works as an alternative solution for try and catch blocks. The throws keyword is used instead of try and catch.

Example:

Solution with throws:

void divideNumber() throws ArithmeticException{

         int result = 5/0;

 } 

 And snippet with try and catch:        

void divideNumber(){

   try{

      int result = 5/0;

    }catch(ArithmeticException e){

     ----      // handle exception

    }

} // method end                      

         

The above both solutions are same, but with different keywords.


 Some key points:

1. There can be one try with multiple catch blocks.

2. Try block can be followed by either catch or finally block.

3. Or both can be followed

4. Throws is like warning that exception can be thrown and throw keyword is real accident took place.

I wrote here  https://www.allabtjava.com/2021/01/java-api-support-for-exception-handling.html on checked exceptions and runtime or unchecked exceptions.

Happy coding... :)

   

Java and OOPS concepts

Java is an object oriented programming language which can be downloaded and installed in your local Machine from java.com

To explain java binaries and tools requires block diagram which gives clear picture. For now I brief few important tools.

• JDK - java development toolkit
• JVM - Java virtual machine
• JRE - Java Run time environment

From oracle site we can download JDK which is shipped along with JVM and JRM. Mostly java programmers need the JDK. For end users JRE alone is enough.

Basic OOPS characteristics are

Inheritance

Encapsulation

Abstraction

and Polymorphism

The above concepts collectively makes application software extendable and changeable with less effort.
Also helps in Developing design patterns. Design patterns gives solutions for common challenges usually a programmer faces while development applications.
Factory design pattern, Abstract design pattern, Builder pattern etc. I explain these Design patterns in another article.

Inheritance:
Inheritance is all about reusing one class behavior and members in it's child class. In java terminology these classes are called as super class and sub class. If class B extends class A then, class A becomes super class and class B becomes class A's sub class.

public class A{

  public A(){

 }

   -------

}

public class B extends A{

   public B(){

    } 

    -------

}   

Encapsulation:
Encapsulation is a technique of putting the source code all together within a unit. Java uses class and interface as keywords to represent unit. Data Hiding is one of the buzzwords which is possible only with implementation of Encapsulation in the program.

Abstraction:
Abstraction is the concept of hiding the irrelevant data from client/user visibility. To implement this feature java uses abstract keyword. this can be be prefixed to a class and methods. Once the class is abstract class then it's object can not be created. And id one or all methods of same class are followed by abstract keyword it can not be implemented.
The point here is java programming language gives implementation freedom to the developers where ever expected.
Sometimes java program is written to a another programmer rather a end user. Usually this code is called Application programming interface in short API. When a programmer writes a program with the intention to be used by another programmer, He/She may not need all the details [line by line] instruction's description is not required. Right?
The punch line is abstraction helps in showing only relevant data to the client of our program.
One of the mostly used design pattern is abstract factory design pattern.

Polymorphism:
In generic terminology poly means many morph means forms. It means many forms of a single method names.
Polymorphism can be achieved within the class or using inheritance i.e extends keyword.

Overloading and overriding:

Overloading rules:
within the class a same method can be duplicated but accepts different arguments and returns different result

1.       Number of arguments must be different
2. Or  Sequence of arguments must be different
3. Or  Type of the arguments must be different.

Uses:
Let us take a method .
     int add(int a, int b){

        return a+b;

     }

Now let us overload this method to add decimal values
 float add(float a, float b){

     return a+b;

 }

Now based on the arguments passed to the add() respect add() method will be invoked.
Overriding:
Overriding is possible only by using inheritance.For an instance super class has add(int a, int b). and sub class also needs add operation but computes differently. Then programmer simply overrides the add() of super class overrides the add() with his new implementation. 

public class SuperClass{

  int add(int a, int b){

       ....

   }

}

public Subclass extends SuperClass{

@Overrides

int add(int a, int b){

// computes his own add operation

}

} 

In next article I write about tools of JDK and JRE and internals of JVM Java Virtual Machine.

Please click the link for more good look and feel and elegant font

Happy Coding. ;-)