regex with or condition to verify two different patterns?

Question

I need to make a regex where I can verify these two patterns. Basically if any of the string is passed from below two patterns, I should be able to verify it.

• First pattern is - I could have strings like this tree1 or tree2. So basically a number preceded by string tree.
• Second pattern is - I can have strings like this tree1a or tree1b or tree2a or tree2b. So tree[number][a-z] for this pattern.

I use below regex but it only works with first pattern. How can I make one regex that can handle both the pattern.

Pattern patternSet = Pattern.compile("^tree[0-9]$");

Answer 1

Your regex should look like so tree\d[a-z]?, so your pattern can be :

Pattern patternSet = Pattern.compile("tree\\d[a-z]?");

If you want more than a digit and more than a letter you can use :

Pattern patternSet = Pattern.compile("tree\\d+[a-z]*");

the last pattern can match tree123, tree1abc or tree123abc

Answer 2

You could add an optional [a-z]? character class

^tree[0-9][a-z]?$

• ^ Start of string
  • tree Match literally
  • [0-9] Match a digit 0-9
  • [a-z]? Optionally match a-z
• $ End of string

Regex demo | Java demo

Pattern patternSet = Pattern.compile("^tree[0-9][a-z]?$");