Java String matches(regex) Examples

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  • Java String matches(regex) method is used to test if the string matches the given regular expression or not.
  • String matches() method internally calls Pattern.matches() method.
  • This method returns a boolean value. If the regex matches the string, it returns “true”, otherwise “false”.
  • If the regex pattern is invalid, PatternSyntaxException is thrown.

Java String matches() Method Implementation

If you look at the source code of the String class, matches() method is implemented like this.

public boolean matches(String regex) {
    return Pattern.matches(regex, this);
}

It’s very similar to the String replaceAll() method.

Java String matches(regex) Examples

Let’s look at some examples of matches() method.

1. Matching String for Two Words of 5 characters

jshell> String str = "Hello World";
str ==> "Hello World"

jshell> str.matches("\\w{5} \\w{5}");
$13 ==> true
Java String Matches Regex Example
Java String matches(regex) Example

The pattern “\w{5}” will match a word having the length as 5.

2. Matching a Positive Integer of any length

We can use “\d+” to match a string having the positive integer data of any length. 

jshell> "1245".matches("\\d+");
$14 ==> true

jshell> "0".matches("\\d+");
$15 ==> true

jshell> "-10".matches("\\d+");
$16 ==> false

jshell> "10.5".matches("\\d+");
$17 ==> false

3. Matching Special Characters

We can use “\W+” to test if a string is made up of only special characters.

jshell> "$%#".matches("\\W+");
$18 ==> true

jshell> "$%#A".matches("\\W+");
$19 ==> false

jshell> "".matches("\\W+");
$20 ==> false

jshell> "_@_".matches("\\W+");
$21 ==> false

jshell> "@".matches("\\W+");
$22 ==> true

Note that the underscore is not considered as a special character. It’s treated as a word character in Java.

4. Case Insensitive Matching

String matches() perform case sensitive matching. If you want case insensitive matching, there are two options.

  1. Use Pattern class directly and compile it with Pattern.CASE_INSENSITIVE flag.
  2. Use (?i) for the whole regex string for the case insensitive comparison.
jshell> "a".matches("A");
$23 ==> false

jshell> "a".matches("(?i)A");
$24 ==> true

Conclusion

Java String matches(regex) is a utility method to quickly test if the string matches a regex or not. If you want to perform more complex operations, it’s better to use Pattern class.

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