Pattern Matching with Regular Expressions - Java

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Printing All Occurrences of a Pattern

Problem

You need to find all the strings that match a given regex in one or more files or other sources.

Solution

This example reads through a file one line at a time. Whenever a match is found, I extract it

from the line and print it.

This code takes the group() methods from Finding the Matching Text , the substring meth-

od from the CharacterIterator interface, and the match() method from the regex and

simply puts them all together. I coded it to extract all the “names” from a given file; in run-

ning the program through itself, it prints the words import , java , until , regex , and so on,

each on its own line:

C:\\> javac -d . ReaderIter.java

C:\\> java regex.ReaderIter ReaderIter.java

import

java

util

regex

import

java

io

Print

all

the

strings

that

match

given

pattern

from

file

Java

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