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Explain the Java regular expression construct "re?".
The subexpression/metacharacter “re?” matches 0 or 1 occurrence of the preceding expression.
Example 1
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class RegexExample {
public static void main( String args[] ) {
String regex = "Wel?";
String input = "Welcome to Tutorialspoint";
Pattern p = Pattern.compile(regex);
Matcher m = p.matcher(input);
int count = 0;
while(m.find()) {
count++;
}
System.out.println("Number of matches: "+count);
}
}Output
Number of matches: 1
Example 2
Following Java program accepts a string from the user, verifies whether it contains alphabet (both cases), It also accepts digits.
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Test {
public static void main( String args[] ) {
String regex = "[a-zA-Z][0-9]?";
Scanner sc = new Scanner(System.in);
System.out.println("Enter an input string: ");
String input = sc.nextLine();
//Creating a Pattern object
Pattern p = Pattern.compile(regex);
//Creating a Matcher object
Matcher m = p.matcher(input);
if(m.find()) {
System.out.println("Match occurred");
} else {
System.out.println("Match not occurred");
}
}
}Output 1
Enter an input string: sample text Match occurred
Output 2
Enter an input string: sample text 34 56 Match occurred
Output 3
Enter an input string: 32 89 45 63 Match not occurred
Updated on: 19-Nov-2019
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