How to use RegExp in Java

11/30/2012

This tutorial shows who to run an simple Regular Expression in Java. First it defines 2 simple Regular Expressions or RegExp to test if a String is a valid 5 digit or 9 digit zipcode. Then the main method defines a list of Strings containing the possible zip code to test. Finally, the code loops through the Strings and test if any matches the 2 patterns. If it does a message with the matching regexp is written in the output, else just an error is written.

Create the following java file:

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Pattern;

public class RegexpPostalCode {
    // 5 digits pattern
    public static final Pattern PATTERN_5_DIGITS = Pattern.compile("\\d{5}");
    // 9 digits pattern
    public static final Pattern PATTERN_9_DIGITS = Pattern.compile("\\d{5}-\\d{4}");

    public static void main(String[] argv) {
        // Define the list
        List<String> myList = new ArrayList<String>();

        // Add the values
        myList.add("95012");
        myList.add("11");
        myList.add("abcde");
        myList.add("abcde-abcd");
        myList.add("95012-1234");
        myList.add("95012.1234");

        // Loop on the list
        for (String current : myList) {
            // Test the 5 digits pattern
            if (PATTERN_5_DIGITS.matcher(current).matches()) {
                System.out.println(current + " is a 5 digit zipcode!");
            } // Test the 9 digits pattern
            else if (PATTERN_9_DIGITS.matcher(current).matches()) {
                System.out.println(current + " is a 9 digit zipcode!");
            } else {
                System.out.println(current + " is not a zipcode.");
            }
        }
    }
}

The output will be:

95012 is a 5 digit zipcode!
11 is not a zipcode.
abcde is not a zipcode.
abcde-abcd is not a zipcode.
95012-1234 is a 9 digit zipcode!
95012.1234 is not a zipcode.

References:

Java Pattern
US Zip codes

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