Golden Rule of Regex Matching

• "If there is more than one regular expression that matches the longest portion of the input (i.e., they all match the same input), the generated scanner chooses the expression that appears first in the specification."

Is = "is"

Island = "island"

Other = [^\r\n]+

%%

{Is} { System.out.println("Got an 'is'"); }

{Island} { System.out.println("Got an 'island'"); }

{Other} { System.out.println("Got other"); }

mylexer.flex

See example12

Input:

island

Output:

Got an 'island'

Is = "is"

Island = "island"

Other = [^\r\n]+

%%

{Is} { System.out.println("Got an 'is'"); }

{Other} { System.out.println("Got other"); }

{Island} { System.out.println("Got an 'island'"); }

mylexer.flex

Input:

island

Output:

Got other

[Actually the {Island}

regular expression will

never be matched!]

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