2220. minimum bit flips to convert a number

class Solution {
    public int minBitFlips(int start, int goal) {
        String ki=bits(start);
        String ai=bits(goal); 
        int i=0;
        int j=0;
        int c=0;
    System.out.println(ki);   
     System.out.println(ai);
     
        if(ki.length()>ai.length()){
            int l=0;
            int k=ki.length()-ai.length();
            while(l!=k){
                ai+='0';
                l++;
            }
        }
         if(ki.length()<ai.length()){
            int l=0;
            int k=ai.length()-ki.length();
            while(l!=k){
                ki+='0';
                l++;
            }
        }
        while(i<ki.length() && j<ai.length()){
            if(ki.charAt(i)!=ai.charAt(j))
            {
                c++;
            }
            i++;j++;
        }
     System.out.println(ki);   
     System.out.println(ai);
       
        return c;
    }
    public String bits(int a)
    { String p="";
        while(a!=0)
        {
           int pi=a%2;
           if(pi==0){
            p+='0';
           }
           else{
            p+='1';
           }
            a=a/2;
        }
       
        return p;
    }
   
}