Java Code House

import java.awt.*;
import javax.swing.*;

public class JProgressBar_Demo {
    //initializing components
 private JFrame frame = new JFrame("Java Swing Examples");
    private JLabel headerLabel = new JLabel("", JLabel.CENTER);
    private JPanel 
                    controlPanel = new JPanel(),
                    contentPanel = new JPanel();
    
    private JProgressBar progressBar;
    private Task task;
    private JButton startButton;
    private JTextArea outputTextArea;

    public JProgressBar_Demo(){
       buildGUI();
    }
    
    public static void main(String[] args){
     JProgressBar_Demo  swingDemo = new JProgressBar_Demo();      
     swingDemo.showDemo();
    }   
    
    private void buildGUI(){
     frame.setSize(350,400);  //stting frame size
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     setLayouts();
     //adding panels to the main panel
     contentPanel.add(headerLabel);
     contentPanel.add(controlPanel);
     frame.getContentPane().add(contentPanel);  //adding main panel to frame
     frame.setVisible(true);
    }
    //sets layout of the panels
    private void setLayouts(){
     //deliberately choosing 3 rows though have 2 components
     contentPanel.setLayout(new GridLayout(3,1));
     //to add in a directional flow
     controlPanel.setLayout(new FlowLayout());
    }
    
    public void showDemo(){
     headerLabel.setText("Component in action : JProgressBar"); 

     progressBar = new JProgressBar(0, 100);
     progressBar.setValue(0);
     progressBar.setStringPainted(true);
     startButton = new JButton("Start");

     outputTextArea = new JTextArea("",5,20);
     //adding scroller to the text-area
     JScrollPane scrollPane = new JScrollPane(outputTextArea);    
     //adding event listener
     startButton.addActionListener(
          //use of lambda expression intead new ActionListener()
       e -> {
        /* all tasks other tan component update in event listeners
           should be carried out in seperate thread */
        task = new Task();                
        task.start();
      });
     //adding components
     controlPanel.add(startButton);
     controlPanel.add(progressBar);
     controlPanel.add(scrollPane);
     frame.setVisible(true);  
    }

    //This class carries out the task when start button is clicked
    private class Task extends Thread {    
     public void run(){
      for(int i =0; i<= 100; i+=10){
       //lambda expression can use only final or pseudo-final variables
       final int progress = i;
       //update swing components in event-dispatch thread
       SwingUtilities.invokeLater(
        //lambda expression instead of new Runnable()
        () -> {
         progressBar.setValue(progress);
         outputTextArea.append(String.format("%d%% of task completed.\n", progress));
        }
       );
       try {
        Thread.sleep(100);
       } catch (InterruptedException e) {}
      }
     }
    }   
}