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.

Today I am going to show you how to use the swing component - JProgressBar in your GUI application. In this article , I will also focus on how to use lambda expression in swing application. You must have seen a progress bar in many applications. It actually is used to denote graphically the amount of task or work that is completed. The basic properties are :

• 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

Today I am going to take you through the basics of annotation. This feature was introduce in JDK 5. Most of the time while writing programs you may have to provide some meta information along with your codes. In those cases annotations come into picture.
What is an annotation ?
Annotation is a metadata that provides data or information about a program which is not a part of the program itself with no direct effect on the code it annotates.

Uses of annotation

• 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.

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);
}

Now earlier you had to mention the criteria by anonymous class like this while calling printSongs() method. Here we are trying to print all songs in list that are released after year 2010.

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

But now with lambda expression the whole thing looks much simpler as shown below

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

The main method of the Song class where both approaches are shown

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); 
}

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Download comlete source from below links which contains Song class with main method where both anonymous class and lambda expressions are used at the same time for better understanding.
DOWNLOAD the source from Mediafire
DOWNLOAD the source from 4shared

One of the frequent question related to Java is whether Java a pure object oriented language or not is often asked in an interview. The answer is NO. There are many things in Java which are not objects e.g. primitive data types like boolean, int, float etc., different kinds of arithmetic, logical and bitwise operator e.g. +, -. *, /, &&, || etc. Few pure OO languages are Smalltalk and Eiffel. Though Java is one of the most successful Object oriented programming language, which also got some functional programming touch in Java 8 is never considered 100% or pure object-oriented programming language. If it were, all its primitives would be objects. It actually moves half-way in this direction with String and Array, but it doesn't quite go far enough.

There are seven qualities to be satisfied for a programming language to be pure Object Oriented.

• Encapsulation/Data Hiding
• Inheritance
• Polymorphism
• Abstraction
• All predefined types are objects
• All operations are performed by sending messages to objects
• All user defined types are objects.

Java supports Encapsulation at class and package level, It supports Abstraction, Inheritance and Polymorphism, and all user defined types are also objects. What it doesn't support is #5 and #6.

package com.javaingrab.security.encrypt;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;


public class AESEncryptor {

 public void encrypt(String fname) throws Exception{
  KeyGenerator keyGen = KeyGenerator.getInstance("AES");
  keyGen.init(256);  //using AES-256
  SecretKey key = keyGen.generateKey();  //generating key
  Cipher aesCipher = Cipher.getInstance("AES");  //getting cipher for AES
  aesCipher.init(Cipher.ENCRYPT_MODE, key);  //initializing cipher for encryption with key
  
  //creating file output stream to write to file
  try(FileOutputStream fos = new FileOutputStream(fname+".aes")){
   //creating object output stream to write objects to file
   ObjectOutputStream oos = new ObjectOutputStream(fos);
   oos.writeObject(key);  //saving key to file for use during decryption

   //creating file input stream to read contents for encryption
   try(FileInputStream fis = new FileInputStream(fname)){
    //creating cipher output stream to write encrypted contents
    try(CipherOutputStream cos = new CipherOutputStream(fos, aesCipher)){
     int read;
     byte buf[] = new byte[4096];
     while((read = fis.read(buf)) != -1)  //reading from file
      cos.write(buf, 0, read);  //encrypting and writing to file
    }
   }
  }
  
 }
 
 public void decrypt(String fname)throws Exception{
  SecretKey key =null;
    
  //creating file input stream to read from file
  try(FileInputStream fis = new FileInputStream(fname)){
   //creating object input stream to read objects from file
   ObjectInputStream ois = new ObjectInputStream(fis);
   key = (SecretKey)ois.readObject();  //reading key used for encryption
   
   Cipher aesCipher = Cipher.getInstance("AES");  //getting cipher for AES
   aesCipher.init(Cipher.DECRYPT_MODE, key);  //initializing cipher for decryption with key
   //creating file output stream to write back original contents
   try(FileOutputStream fos = new FileOutputStream(fname+".dec")){
    //creating cipher input stream to read encrypted contents
    try(CipherInputStream cis = new CipherInputStream(fis, aesCipher)){
     int read;
     byte buf[] = new byte[4096];
     while((read = cis.read(buf)) != -1)  //reading from file
      fos.write(buf, 0, read);  //decrypting and writing to file
    }
   }
  }
 
 }
 
 public static void main(String[] args) throws Exception {
  AESEncryptor obj = new AESEncryptor();
  obj.encrypt("clear.txt");
  obj.decrypt("clear.txt.aes");
 }

}

NOTE : You will need the clear.txt file which is the file to be encrypted to execute the code. The encrypted file will be placed in the same directory with same name as original file but with an extension ".aes". The decrypted file will have the same name as the encrypted file but with extension ".dec", this is done deliverately for you people to check whether the original conetents are same as the decrypted one.
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DOWNLOAD the source from Mediafire