Introduction
The matches() method in Java is a powerful tool for validating strings against regular expressions. It checks if the entire input string conforms to the pattern defined by the regex.
Syntax
public boolean matches(String regex)
Parameters
| Parameter | Description |
|---|---|
regex |
The regular expression to which the string is matched. |
Return Value
This method returns true if the entire sequence of characters in the input string matches the given regular expression; otherwise, it returns false.
Examples
Example 1: Basic Pattern Matching
Let's start with a simple example. This example demonstrates how to check if a string consists only of digits using the regex "\d+".
public class MatchesExample1 {
public static void main(String[] args) {
String str1 = "12345";
String str2 = "abc123";
System.out.println("" + str1 + " matches: " + str1.matches("\d+")); // Matches only digits
System.out.println("" + str2 + " matches: " + str2.matches("\d+"));
}
}
12345 matches: true
abc123 matches: falseIn this example, str1 contains only digits, so it successfully matches the regex. str2 contains both letters and numbers, failing the match.
Example 2: Matching a Specific Format (Email)
This example shows how to validate an email address using a simplified regular expression for emails.
public class MatchesExample2 {
public static void main(String[] args) {
String email1 = "test@example.com";
String email2 = "invalid-email";
System.out.println("" + email1 + " matches: " + email1.matches("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}"));
System.out.println("" + email2 + " matches: " + email2.matches("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}"));
}
}
test@example.com matches: true
invalid-email matches: falseThe regex [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} is a simplified pattern for emails. It's important to note that a truly robust email validation requires a much more complex regular expression, as the rules are quite intricate.
Example 3: Using Character Classes
This example uses character classes to match strings containing only lowercase letters.
public class MatchesExample3 {
public static void main(String[] args) {
String str1 = "lowercase";
String str2 = "MixedCase";
System.out.println("" + str1 + " matches: " + str1.matches("[a-z]++"));
System.out.println("" + str2 + " matches: " + str2.matches("[a-z]++"));
}
}
lowercase matches: true
MixedCase matches: falseThe regex [a-z]+ specifies that the string must contain only lowercase letters. Therefore, "lowercase" matches, while "MixedCase" does not.
Example 4: Matching with Quantifiers
This example uses quantifiers to match strings that start with one or more digits followed by some characters.
public class MatchesExample4 {
public static void main(String[] args) {
String str1 = "123abc";
String str2 = "abc";
System.out.println("" + str1 + " matches: " + str1.matches("\d+.*+"));
System.out.println("" + str2 + " matches: " + str2.matches("\d+.*+"));
}
}
123abc matches: true
abc matches: falseThe regex \d+.∗+ requires at least one digit (\d+) followed by any characters (.∗+). Thus, “123abc” successfully matches because it starts with digits.
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