You can use a BreakIterator to determine sentence boundaries. You start by creating a BreakIterator with the getSentenceInstance method:

BreakIterator sentenceIterator = BreakIterator.getSentenceInstance(currentLocale);

To show the sentence boundaries, the program uses the markBoundaries method, which is discussed in the section Word Boundaries. The markBoundaries method prints carets (^) beneath a string to indicate boundary positions. Here are some examples:

She stopped.  She said, "Hello there," and then went on.
^             ^                                         ^

He's vanished!  What will we do?  It's up to us.
^               ^                 ^             ^

Please add 1.5 liters to the tank.
^                                 ^