String-2 > doubleChar 

Problem: :

Given a string, return a string where for every char in the original, there are two chars.

Test Cases:

doubleChar("The") → "TThhee"
doubleChar("AAbb") → "AAAAbbbb"
doubleChar("Hi-There") → "HHii--TThheerree"

Solution:

public String doubleChar(String str) {

  String s=str,s1="";

for(int i=0;i<s.length();i++)

{

s1+=s.substring(i,i+1)+s.substring(i,i+1);

}

return s1;

}