19 Jan Java Regular Expressions
To perform search and manipulation on strings in Java, use Regex i.e., Regular Expressions. To form a search pattern, match or find strings, and search and edit strings, we use Regular Expressions as a sequence of characters. To work with regex in Java, import the java.util.regex package:
- Pattern Class
- Matcher Class
Pattern Class
A Pattern class is a compiled representation of a regular expression to define a pattern. For a pattern, call its compile() method to return a Pattern object.
Matcher Class
The Matcher Class performs match operations on a character sequence by interpreting a Pattern. For a Matcher object, call the matcher() method on a Pattern object.
How to write a Regular Expression in Java
To write a Regex in Java, we used both the Pattern and Matcher class. Let us see two examples.
Example 1
In this first example, we will search for a letter in a word with Regular Expressions in Java. If it is found, True gets displayed. The pattern is case insensitive, set using the Flag Pattern.CASE_INSENSITIVE:
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import java.util.regex.Matcher; import java.util.regex.Pattern; class Studyopedia { public static void main(String args[]){ // Here . means a single character Pattern pattern = Pattern.compile(".k", Pattern.CASE_INSENSITIVE); Matcher match = pattern.matcher("tK"); boolean res = match.matches(); System.out.println("Match Found: "+res); } } |
Output
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Match Found: true |
Example 2
In the next example, we will find a letter in a word with Regular Expressions in Java:
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import java.util.regex.Matcher; import java.util.regex.Pattern; class Studyopedia { public static void main(String args[]){ // Here . means a single character boolean res = Pattern.compile(".k").matcher("tk").matches(); System.out.println("Match Found: "+res); } } |
Output
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Match Found: true |
Regex Quantifiers
To define quantities i.e., the occurrences of a character, Regex in Java has Quantifiers. Here is the list of Quantifiers in Java that matches any string containing,
Let us now see an example of Quantifiers in Regular Expressions:
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import java.util.regex.Matcher; import java.util.regex.Pattern; class Studyopedia { public static void main(String args[]){ System.out.println("Quantifier example..."); // Returns true since p or q or r or s appears once System.out.println(Pattern.matches("[pqrs]?", "p")); // Returns false since r appears more than one times System.out.println(Pattern.matches("[pqrs]?", "rrrr")); // Returns false since p, q, r and s appears more than one times System.out.println(Pattern.matches("[pqrs]?", "ppqqrrss")); } } |
Output
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Quantifier example... true false false |
Regex Metacharacters
The following are the metacharacters in Regular Expressions and finds,
Let us now see an example of Metacharacters in Regular Expressions:
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import java.util.regex.Matcher; import java.util.regex.Pattern; class Studyopedia { public static void main(String args[]){ System.out.println("Metacharacters example..."); // Returns false since it is a non-digit System.out.println(Pattern.matches("\\d", "pqrst")); // Returnstrue since it is a digit and appears once System.out.println(Pattern.matches("\\d", "5")); // Returns false since it is a digit and appears more than once System.out.println(Pattern.matches("\\d", "228")); // Returns false since it is a non-digit and appears more than once System.out.println(Pattern.matches("\\D", "pqrst")); } } |
Output
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Metacharacters example... false true false false |
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