BlueJ Program On Caesar Cipher

Caesar Cipher is an encryption technique which is implemented as ROT13 (‘rotate by 13 places’). It is a simple letter substitution cipher that replaces a  letter with the letter 13 places after it in the alphabets, with the other characters remaining unchanged. 

Example 1 

INPUT : Hello! How are you? 

OUTPUT : The cipher text is: Uryyb? Ubj ner lbh? 

Example 2 

INPUT : Encryption helps to secure data.

OUTPUT : The cipher text is: Rapelcgvba urycf gb frpher qngn. 

Example 3

INPUT : You

OUTPUT : INVALID LENGTH

import java.io.*; 

class Pat 

{

BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); 

String s,str=""; 

int a; 

char ch;

void takeString() throws Exception 

{ 

System.out.print("\nEnter the sentence:"); 

s=br.readLine().trim();

 if(s.length() >100) 

{

System.out.print("\nInvalid Length of String:");

 return; 

}

for(int i = 0; i< s.length();i++) 

{

ch = s.charAt(i); 

if(Character.isLetter(ch)) 

{

a = ch + 13;

if((Character.toUpperCase(ch) > 90) ||(Character.toLowerCase(ch) > 122)) 

{ 

a = a - 26; 

} 

ch = (char)a; 

} 

str = str + ch;

}

 System.out.println("The cipher text is :"+str); 

} 

public static void main(String args[]) throws Exception 

{ 

Pat ob = new Pat(); ob.takeString();

} 

}

Back To 2017 ISC Practical Paper: Click Here