Java Regex

Putting this up for my own reference more than any other reason. Java Regex are useful in manipulation strings. A regex consist of pattern blocks and optional quantifiers.

Pattern Blocks

some patterns are built in to java,

\d - digit

\w – word character

\s – whitespace

if a range of characters need to be used as a pattern it should be put as follows,

[a-z] – a to z simple

[a-zA-Z] - a to z capital and simple

[1-9] – 1 to 9

Quantifiers

these add meaning to the patterns. They should be added immediately after the pattern.

* - match pattern 0 or more times

+ - match pattern 1 or more times

{n} - match pattern exactly n times

{n,m} – match pattern between n to m times

Regex Examples

[a-zA-Z]* - a to z capital and simple 0 or more times

[a-zA-Z]+ - a to z capital and simple 1 or more times

\d{2,5} – digits 2 to 5 times

[.]*[a-zA-Z]{1,5} - . 0 or more times in the beginning followed by a to z capital and simple 1 to 5 time, the whole pattern once.