This is an Java(J2SE) implementation for the playfair cipher en-decription technique .
It is a GUI program that ask the user to enter the encription key and then type the plain text and then press Encript button to encript and the cipher text will be desplayed.

import java.util.Scanner;


public class playfair {

private String KeyWord=new String();
private String Key=new String();
private char matrix_arr[][]= new char[5][5];

public void setKey(String k)
{
// This function will take the input key from the user
// Then it'll remove duplication of letters from the key
// Will add it to the private KeyWord for matrix generation

String K_adjust=new String();
boolean flag = false;

K_adjust = K_adjust + k.charAt(0);

for(int i=1; i<k.length();i++)
{
for(int j=0;j<K_adjust.length(); j++)
{
if(k.charAt(i)==K_adjust.charAt(j))
{
flag = true;
}
}

if(flag == false)
K_adjust = K_adjust + k.charAt(i);

flag = false;
}

KeyWord=K_adjust;
}

public void KeyGen()
{
// This function adjust the alphabetical letters adding the
// KeyWord on the beginning of them & then it calls the matrix function

boolean flag=true;
char current;

Key=KeyWord;

for ( int i=0 ; i<26 ; i++)
{
current=(char)(i+97);

if(current=='j')
continue;

for(int j=0 ; j< KeyWord.length() ; j++ )
{
if (current == KeyWord.charAt(j))
{
flag=false;
break;
}
}

if(flag)
Key=Key+current;

flag=true;
}

System.out.println(Key);
matrix ();

}

private void matrix ()
{
int counter=0;

for (int i=0 ; i<5 ;i++)
{
for (int j=0 ; j<5 ; j++)
{
matrix_arr[i][j]=Key.charAt(counter);
System.out.printf("%s ",matrix_arr[i][j]);

counter++;
}

System.out.println("\n");
}
}

private String format(String old_text)
{
// This function is to adjust the Text to encrypt
// It changes all the 'j' letters to 'i' & add 'x' character
// between repeatable pairs.

int i = 0;
int j = 0;
int len = 0;
String text = new String();
len = old_text.length();

//System.out.println(old_text);
/*** Change all j's into i's *****/
for (int tmp = 0; tmp < len; tmp++)
{
if (old_text.charAt(tmp) == 'j')
{
text = text + 'i';
}
else
text = text+old_text.charAt(tmp);
}
/**********************************/
len = text.length();
/*** Assign 'x' to letters that repeat in a diagram ***/
for (i = 0; i < len; i = i + 2) //run for half of string length
{
if (text.charAt(i+1) == text.charAt(i)) //if char = previous char
{
text = text.substring(0, i+1) + 'x' + text.substring(i+1);
}
else //not a repeat character, move along
{}
}
return text;
}

private String [] Divid2Pairs (String new_string)
{
String Original = format(new_string);

int size= Original.length();

if(size%2!=0)
{
size++;
Original = Original+'x';
}

String x[]= new String[size/2];

int counter=0;

for ( int i=0 ; i<size/2 ;i++)
{
x[i]=Original.substring(counter, counter+2);
System.out.println(x[i]);
counter=counter+2;
}

return x;
}

public int[] GetDiminsions(char letter)
{
int []key=new int[2];

if ( letter == 'j')
letter='i';

for (int i=0 ; i<5 ;i++)
{
for (int j=0 ; j<5 ; j++)
{
if(matrix_arr[i][j] == letter)
{
key[0]=i;
key[1]=j;
break;
}
}

}

return key;
}

public String Encript(String Source)
{
System.out.println("Encription Start");

String src_arr[]=Divid2Pairs(Source);

String Code=new String();

char one;
char two;

int part1[]=new int[2];
int part2[]=new int[2];

//start on pair by pair
for (int i=0 ; i< src_arr.length ;i++ )
{
one = src_arr[i].charAt(0);//get first char
two = src_arr[i].charAt(1);//get second char

part1 = GetDiminsions(one);//get position of the first char
part2 = GetDiminsions(two);//get position of the second char

//check for special cases
if(part1[0]==part2[0])//same row
{
if (part1[1]<4)
part1[1]++;
else
part1[1]=0;

if(part2[1]<4)
part2[1]++;
else
part2[1]=0;

}

else if (part1[1]==part2[1]) //same column
{
if (part1[0]<4)
part1[0]++;
else
part1[0]=0;

if(part2[0]<4)
part2[0]++;
else
part2[0]=0;
}
else
{
int temp=part1[1];
part1[1]=part2[1];
part2[1]=temp;
}

Code= Code + matrix_arr[part1[0]][part1[1]] + matrix_arr[part2[0]][part2[1]];
}
System.out.println(Code);
return Code;
}

public String Decript (String Code)
{
System.out.println("Decription Start");

String Original=new String();

String src_arr[]=Divid2Pairs(Code);

char one;
char two;

int part1[]=new int[2];
int part2[]=new int[2];


//start on pair by pair
for (int i=0 ; i< src_arr.length ;i++ )
{
one = src_arr[i].charAt(0);//get first char
two = src_arr[i].charAt(1);//get second char

part1 = GetDiminsions(one);//get position of the first char
part2 = GetDiminsions(two);//get position of the second char

//check for special cases
if(part1[0]==part2[0])//same row
{
if (part1[1]>0)
part1[1]--;
else
part1[1]=4;

if(part2[1]>0)
part2[1]--;
else
part2[1]=4;
}

else if (part1[1]==part2[1]) //same column
{
if (part1[0]>0)
part1[0]--;
else
part1[0]=4;

if(part2[0]>0)
part2[0]--;
else
part2[0]=4;
}
else
{
int temp=part1[1];
part1[1]=part2[1];
part2[1]=temp;
}


Original =Original + matrix_arr[part1[0]][part1[1]] + matrix_arr[part2[0]][part2[1]];
}

System.out.println(Original);
return Original;
}
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub

playfair x=new playfair();

Scanner sc = new Scanner(System.in);

System.out.println("Enter a lower case keyword:");
String keyword = sc.next();
x.setKey(keyword);
x.KeyGen();

System.out.println("To Encrypt enter 1 \nTo Decript enter 2\nTesting both enter anything else:");
int choosen_value = sc.nextInt();

if(choosen_value==1)
{
System.out.println("Enter a lower case word to encrypt:");
String key_input = sc.next();
String Encripted= x.Encript(key_input);
}
else if(choosen_value==2)
{
System.out.println("Enter a lower case word to decrypt:");
String decripted = sc.next();

x.Decript(decripted);
}
else
{
System.out.println("Enter a lower case word to encrypt & decrypt:");
String key_input = sc.next();

String Encripted= x.Encript(key_input);
x.Decript(Encripted);
}
}
}