Playfair_Cipher_Decode.java

import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class Playfair_Cipher_Decode {
	public static String decipher(String inputText, String[][] array) { 
		String output = "";
		int position11 = 0; 
		int position12 = 0;         
		int position21 = 0; 
		int position22 = 0; 
		int last = 2;   
		char c1 = inputText.charAt(0); 
		char c2 = inputText.charAt(0); 
		// decipher the text, two letters at a time 
		for (int a = 1; a < inputText.length(); a++) { 
			if (inputText.substring(a, a + 1).equalsIgnoreCase(" ") != true && inputText.substring(a + 1, a + 2).equalsIgnoreCase(" ") != true && a != last) { 
				// find the position of the first letter in the array/square
				for (int i = 0; i < 5; i++) { 
					for (int j = 0; j < 5; j++) { 
						if (inputText.substring(a, a + 1).equalsIgnoreCase(array[i][j]) == true) { 
							position11 = i; 
							position12 = j; 
							c1 = inputText.charAt(a); 
						}
					} 
				} 
				// find the position of the second letter in the array/square
				for (int k = 0; k < 5; k++) { 
					for (int l = 0; l < 5; l++) { 
						if (inputText.substring(a + 1, a + 2).equalsIgnoreCase(array[k][l]) == true) { 
							position21 = k; 
							position22 = l; 
							c2 = inputText.charAt(a + 1); 
						}
					} 
				} 
				// now reverse the enciphering process - e.g. if they are in the same row, then instead of 
				// moving to the right, move each letter to the left - producing the plain text letters! 
				// see the enciphering program for details! 
				// are they in the same row? 
				if (position11 == position21) { 
					if (position12 != 0) { 
						position12--; 
						if (Character.isUpperCase(c1) == true) { 
							output = output + array[position11][position12].toUpperCase();  
				 		} else { 
							output = output + array[position11][position12]; 
				 		}
					} else { 
						position12 = 4; 
						if (Character.isUpperCase(c1) == true) { 
							output = output + array[position11][position12].toUpperCase();  
				 		} else { 
							output = output + array[position11][position12]; 
				 		}
					} 
					if (position22 != 0) { 
						position22--;
						if (Character.isUpperCase(c2) == true) { 
							output = output + array[position21][position22].toUpperCase(); 
						} else { 
							output = output + array[position21][position22]; 
						} 
					} else { 
						position22 = 4; 
						if (Character.isUpperCase(c2) == true) { 
							output = output + array[position21][position22].toUpperCase(); 
						} else { 
							output = output + array[position21][position22]; 
						} 
					} 
					// are they in the same column? 
				} else if (position12 == position22) { 
					if (position11 != 4) { 
						position11++; 
						if (Character.isUpperCase(c1) == true) { 
							output = output + array[position11][position12].toUpperCase(); 
						} else { 
							output = output + array[position11][position12];
						}
					} else { 
						position11 = 0; 
						if (Character.isUpperCase(c1) == true) { 
							output = output + array[position11][position12].toUpperCase(); 
						} else { 
							output = output + array[position11][position12];
						}
					} 
					if (position21 != 4) { 
						position21++; 
						if (Character.isUpperCase(c2) == true) { 
							output = output + array[position21][position22].toUpperCase(); 
						} else { 
							output = output + array[position21][position22]; 
						} 
					} else { 
						position21 = 0; 
						if (Character.isUpperCase(c2) == true) { 
							output = output + array[position21][position22].toUpperCase(); 
						} else { 
							output = output + array[position21][position22]; 
						}
					} 
				// they are in neither the same row nor the same column! 
				} else { 
					if (Character.isUpperCase(c1) == true) { 
						output = output + array[position11][position22].toUpperCase(); 
					} else { 
						output = output + array[position11][position22]; 
					}
					if (Character.isUpperCase(c2) == true) { 
						output = output + array[position21][position12].toUpperCase(); 
					} else { 
						output = output + array[position21][position12]; 
					} 
				}
				last = a + 1; 
			} else if (inputText.substring(a, a + 1).equalsIgnoreCase(" ") == true) { 
				output = output + " "; 
			} 
		} 
		return output;
	}
	public static void main(String[] args) { 
		String inputKeyword = ""; 
		boolean valid = false; 
		// the validation mechanism for the keyword
		while (valid == false) { 
			inputKeyword = JOptionPane.showInputDialog(null,"Please enter your keyword"); 
			inputKeyword = inputKeyword.trim(); 
			inputKeyword = inputKeyword.toLowerCase();
			valid = true;
			// check if there are any spaces 
			if (inputKeyword.contains(" ") == true) { 
				valid = false;
				System.out.println("The key word cannot contain any spaces!");
			// check if there are any numbers 
			} else if (inputKeyword.matches(".*[0-9].*") == true) {
				valid = false;
				System.out.println("The key word cannot contain any numbers!");
			// check if there are any special characters 
			} else if (inputKeyword.matches("[a-zA-Z0-9 ]*") == false) {
				valid = false;
				System.out.println("The key word cannot contain any special characters!");
			// check if a keyword has been entered 
			} else if (inputKeyword.length() < 1 == true) {
				valid = false;
			}
		} 
		inputKeyword = inputKeyword.toLowerCase(); 
		String inputText = "";
		valid = false;
		// the validation method for the text
		while (valid == false) { 
			inputText = JOptionPane.showInputDialog(null,"Please enter the text that you wish to decipher");
			inputText = inputText.trim(); 
			inputText = inputText.replaceAll(" ", "");
			valid = true;
			// check that text has been entered 
			if (inputText.length() < 1) { 
				valid = false;
			// check that there are no numbers 
			} else if (inputText.matches(".*[0-9].*") == true) {
				valid = false;
				System.out.println("The text cannot contain any numbers!");
			// check that there are no special characters 
			} else if (inputText.matches("[a-zA-Z0-9 ]*") == false) {
				valid = false;
				System.out.println("The text cannot contain any special characters!");
			}
		} 
		// create the letter square in the form of a 5x5 array 
		String[][] array = new String[5][5]; 
		// initialise the array - ex is just an initial value string 
		for (int i = 0; i < 5; i++) { 
			for (int j = 0; j < 5; j++) { 
				array[i][j] = "ex";   
			} 
		}		
		String string1 = ""; 
		String string2 = ""; 
		boolean accept = false;                           
		int count = 1; 
		// remove repeat letter's in key word 
		if (inputKeyword.substring(0, 1).equalsIgnoreCase("j") == true) { 
			inputKeyword = inputKeyword.substring(1, inputKeyword.length()); 
		} 
		// remove the letter j from the keyword (Playfair ciphers are 5x5 = 25 letters, so i and j are used interchangeably) 
		while (accept == false) { 
				if (inputKeyword.indexOf(inputKeyword.substring(count, count + 1)) != inputKeyword.lastIndexOf(inputKeyword.substring(count, count + 1)) || inputKeyword.substring(count, count + 1).equalsIgnoreCase("j") == true) { 
					string1 = inputKeyword.substring(0, inputKeyword.lastIndexOf(inputKeyword.substring(count, count + 1))); 
					string2 = inputKeyword.substring(inputKeyword.lastIndexOf(inputKeyword.substring(count, count + 1)) + 1, inputKeyword.length()); 
					inputKeyword = string1.concat(string2); 
				} else { 
					count++; 
				} 
				if (count == inputKeyword.length()) { 
					accept = true; 
				} 				
		} 
		int count1 = 0; 
		// fill the array with the key word 
		for (int i = 0; i < 5 && count1 < inputKeyword.length(); i++) { 
			for (int j = 0; j < 5 && count1 < inputKeyword.length(); j++) { 
				array[i][j] = inputKeyword.substring(count1, count1 + 1); 
				count1++;  				
			} 
		} 
		// eliminate character's which are not required 
		String list = "abcdefghiklmnopqrstuvwxyz "; 
		for (int a = 0; a < inputKeyword.length(); a++) { 
			for (int q = 0; q < list.length(); q++) {   
				if (inputKeyword.substring(a, a + 1).equalsIgnoreCase(list.substring(q, q + 1)) == true) { 
					string1 = list.substring(0, q); 
					string2 = list.substring(q + 1, list.length()); 
					list = string1.concat(string2); 
				} 
			} 
		} 
		int count2 = 0; 
		// fill rest of the array 
		for (int i = 0; i < 5; i++) { 
			for (int j = 0; j < 5; j++) { 	
				if (array[i][j].equalsIgnoreCase("ex") == true) { 
					array[i][j] = list.substring(count2, count2 + 1); 
					count2++; 
				} 
			} 
		} 

		string1 = " "; 
		inputText = string1.concat(inputText); 
		inputText = inputText + " "; 
		String output = ""; 
		output = decipher(inputText, array);
		JOptionPane.showMessageDialog(null, output);
	} 
}