What is the difference between String.subString() and String.subSequence()

Question

String.subSequence() has the following javadoc:

Returns a new character sequence that is a subsequence of this sequence.

Answer 1

Substrings are consecutive subsequences.

For example, for sequence abc we have

substrings: a, ab, abc, b, bc, c, and the empty substring;
subsequences: a, b, ab, c, ac, bc, abc, and the empty subsequence.

When the letters are repeated, some substrings and subsequences will look the same.