An easy Caesar Cipher ISC Practical 2017 Program 3

import java.io.*;
public class caeser_cipher
{
    String str,str2="";
    int len;
    void input()throws IOException
    {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.println("enter the string");
        str=br.readLine();
        len=str.length();
    }
    void compute()
    {
        char ch,ch2;
        int l,m;
        for(int i=0;i<len;i++)
        {
            ch=str.charAt(i);
            if(Character.isLetter(ch)==true)
            {l=(int)ch;
            if(l==97||l<=109||l==65||(l<=77&&l<90))
            {
                m=l+13;
                ch2=(char)m;
                str2+=ch2;
            }
            else
            {
                m=l-13;
                ch2=(char)m;
                str2+=ch2;
            }
        }
        else
        str2+=ch;
    }
}
    void display()
    {
        System.out.println("the original string was:"+str);
        System.out.println("the cipher string is:"+str2);     
    }
    public static void main()throws IOException
    {
        caeser_cipher obj=new caeser_cipher();
        obj.input();
        obj.compute();
        
        obj.display();
    }
}