String replaceRange(int start, int end, String replacement)

Replaces the substring from start to end with replacement.

Returns a new string equivalent to:

this.substring(0, start) + replacement + this.substring(end)

The start and end indices must specify a valid range of this string. That is 0 <= start <= end <= this.length. If end is null, it defaults to length.

Source

String replaceRange(int start, int end, String replacement);