Java Code House

• @Deprecated : This annotation is used to indicate that the element marked with it should not be used any longer. The compiler will generate warning if any program uses class, field or method marked with this annotation. It should also be documented with Javadoc annotation @deprecated. Many people make mistakes between the use of @ sign in annotation and javadoc comment. They are completely different and most importantly the annotation has upper-case while the Javadoc comment has a lower-case.

class DeprecationDemo{
   /**
   * @deprecated
   * defines how to use deprecated annotation
   */
   @Deprecated
   public void deprecatedMethod(){}
}

• @Override : This annotation is used to indicate that an element marked with it is meant to override an element of super-class. This is not necessary to override an element but helps to prevent runtime errors if Java fails to override during run-time. To know more why should you use this read our article here
• @SupressWarnings : This annotation is used to supress some warnings that would be generated by the compiler if not used. In our example we will inherit a serializable class JPanel and not write the variable serialVersionUID which will generally result in warnings. But using this annotation will supress it.

@SupressWarnings("serial")
class SupressWarningsDemo extends javax.swing.JPanel{
   
}

It can also be used to supress other warnings like deprecated using "deprecation" if using any deprecated elements. Also unchecked warnings using "unchecked" while interfacing with legacy codes before the inclusion of generics.
• @SafeVarargs : This annotation when applied to a method confirms that there will be no unsafe operation with the variable argument parameter. When it is used unchecked warnings associated with varargs are supressed.
• @FunctionalInterface : This  annotation is used to indicate that an interface is functional interface. this one is related to lambda expression and method references. This annotation is included in Java 8. It can only used with interfaces and if used with classes or enums it will create an error.

• Max/Min value - A progress bar always has a maximum and a minimum value
• Current value - This value is used to denote the current progress

public class JProgressBar
extends JComponent
implements SwingConstants, Accessible

To know more about the JProgressBar class click here
Most often you need it while reading or writing afile. Here in our example, we will carry out a simple task where we just increase an integer value at a step of 10 and set that vakue to the progress bar. Before we assign the next value the thread sleeps for 100ms so that the progress can be viewed easily. Depending on that value a text area is updated.

The output of our demo code

Two most important things must be kept in mind whether its a simple or a complex task. In our example also we have followed that.

• You should always carry out the task in a seperate thread. In our case generating the integer value.
• Always update the progress bar and other swing components in event-dispatch thread only. In our case we set the progress bar value with the integer and update text area.

Also here in our code instead of creating an anonymous inner class of ActionListener and Runnable we have used Lambda Expression.

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Java Source Code

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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) {}
      }
     }
    }   
}

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Download Links

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DOWNLOAD the source from Mediafire
DOWNLOAD the source from 4shared

• Information used by compiler : They can be used which carries special meaning to the compiler and helps in detecting any compile time errors.
• Deployment-time processing : They can be used by softwares, servers to generate codes, files and also to deploy codes as in case of servlets.
• Runtime processing : They can be used to carry information during runtime.

Today I am going to deal with the new feature of Java 8 - Lambda Expression. Here we will go through a short introduction on lambda expression and follow up with a simple example to start with it before going into complex ones in our next articles.

Why Lambda Expressions ?
Earlier befor Java 8, when we didn't have this awesome feature we had to use anonymous inner classes. Suppose you are writing a GUI application where you write anony mous class very often to specify what action is to be taken when a button is clicked. But  now we can use lambdas in places of anonymous classes having a single method. Alternatively you can use them for functional interfaces.In those cases normally we try to pass funtionality as function arguments using anonymous classes. But those codes are cumbersome and look very unclear. So Lambda Expressions has been introduced which allows you to pass functionality as arguments with very simple syntax.

What is the syntax of Lambda Expression ?
Suppose you have a functional interfacelike below which takes a string argument and returns void.

interface IDemo{
   public void action(String s);
}

Now your lambda expression syntax in place of anonymous class is

(a) -> System.out.println(s)

Now if you have more than one parameter then give them seperated by commas as (a,b,c) and so on. As in our case we have only one parameter, you can omit the parenthesis.

Here in our sample example we will create a Song class which will have different attrbutes like tile,album etc. There will be a functional interface that takes a Song object and returns a boolean value. Now there will be a method which takes in a Collection of songs and performs a particular action when they satisfy a particular criteria. Now earlier, you woula have to pass the criteria while calling that function as an anonymous class; but with Java 8 we will do it using Lambda Expression.
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Java Source Code

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package lambda;

import java.util.List;
import java.util.ArrayList;

public class Song {
 //instance variables
 private String title,artist,album;
 private short year,bitrate;
 //constructor to set values
 public Song(String title, String artist, String album, short year, short bitrate) {
  super();
  setTitle(title);
  setArtist(artist);
  setAlbum(album);
  setYear(year);
  setBitrate(bitrate);
 }
  
 public String getTitle() {
  return title;
 }
 public void setTitle(String title) {
  this.title = title;
 }

 public String getArtist() {
  return artist;
 }
 public void setArtist(String artist) {
  this.artist = artist;
 }

 public String getAlbum() {
  return album;
 }
 public void setAlbum(String album) {
  this.album = album;
 }

 public short getYear() {
  return year;
 }
 public void setYear(short year) {
  this.year = year;
 }

 public short getBitrate() {
  return bitrate;
 }
 public void setBitrate(short bitrate) {
  this.bitrate = bitrate;
 }

 @Override
 public String toString() {
  return "Music [title=" + title + ", artist=" + artist + ", album="
    + album + ", year=" + year + ", bitrate=" + bitrate + "]";
 }
 //prints all songs of the list which satisfies the criteria of tester
 public static void printSongs(List<Song> tracks, CheckSong tester){
  for(Song mt : tracks)  //for-each loop
   if(tester.test(mt))  //testing criteria
    System.out.println(mt);  //printing if satisfies
 }
}

//functional interface to check the criteria
interface CheckSong{
        boolean test(Song song);
}

printSongs(tracks, 
               new CheckSong() {
   @Override
   public boolean test(Song song) {
    return song.getYear() > 2010;
   }
});

printSongs(tracks, mt -> mt.year > 2010);

public static void main(String... args){
 List<Song> tracks = new ArrayList<>();
 Song m = new Song("Waka Waka","Shakira","FIFA",(short)2010,(short)320);
 tracks.add(m);
 m = new Song("La La La","Shakira","FIFA",(short)2014,(short)320);
 tracks.add(m);
 System.out.println("With anonymous class");
 printSongs(tracks, 
   new CheckSong() {
    @Override
    public boolean test(Song song) {
     return song.getYear() > 2010;
    }
 });
 System.out.println("With lambda expression");
 printSongs(tracks, mt -> mt.year > 2010); 
}