How to match a string's end using a regex pattern in Java?

You need to match "s", but only if it is the last character in a word. This is achieved with the boundary assertion $:

input.replaceAll("s$", " ");

If you enhance the regular expression, you can replace multiple suffixes with one call to replaceAll:

input.replaceAll("(ed|s)$", " ");

Use $:

Pattern p = Pattern.compile("s$");