2___ replace spaces

Description Title: 
Please implement a function, a string to replace each space to "20%." For example, when the string is We Are Happy. After the string is replaced after We% 20Are% 20Happy.

public  class Solution {
 // use StringBuilder transform 
    public String replaceSpace (the StringBuffer STR) { 
          StringBuilder S = new new StringBuilder ();   // to return results 
        for ( int I = 0; I <str.length (); I ++ ) {
             IF (str.charAt (I) == '') { // if it is replaced with spaces 
                s.append ( "% 20 is" ); 
            } the else { 
                 s.append (str.charAt (I));   // not spaces, without replacing 
            } 
           
        } 
        return s.toString ();   // return result
    }
    }

 String, StringBuilder calculated length by length () method.