Converting a sentence string to a string array of words in Java

String.split() will do most of what you want. You may then need to loop over the words to pull out any punctuation.

For example:

String s = "This is a sample sentence.";
String[] words = s.split("\\s+");
for (int i = 0; i < words.length; i++) {
    // You may want to check for a non-word character before blindly
    // performing a replacement
    // It may also be necessary to adjust the character class
    words[i] = words[i].replaceAll("[^\\w]", "");
}

Now, this can be accomplished just with split as it takes regex:

String s = "This is a sample sentence with []s.";
String[] words = s.split("\\W+");

this will give words as: {"this","is","a","sample","sentence", "s"}

The \\W+ will match all non-alphabetic characters occurring one or more times. So there is no need to replace. You can check other patterns also.