Constructing a String
If you are constructing a string with several appends, it may be more efficient to construct it using a StringBuffer and then convert it to an immutable String object. 

 StringBuffer buf = new StringBuffer("Initial Text");
   
 // Modify
 int index = 1;
 buf.insert(index, "123");   // I123nitial Text
 buf.append("456");          // I123nitial Text456
 buf.delete(1, 4);           // Initial Text456
 buf.replace(12, 15, " XY"); // Initial Text XY
            
 // Convert to string
 String s = buf.toString();  // Initial Text XY