Question

How to use X? , X?? and X?+ regular expressions (REGEX) in Java

Answer 1

package javaapplication1;
 
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class Example {
    public static void main(String[] args) {
        // X? , X?? and X?+  (X once or not at all)
        searchREGEX("", "a?", "a??", "a?+");
    }
     
    private static void searchREGEX(String input, String... regex_list) {
        for (String regex : regex_list) {
            Pattern pattern = Pattern.compile(regex);
            Matcher matcher = pattern.matcher(input);
  
            boolean found = false;
            while (matcher.find()) {
               System.out.println(String.format("%s: Found" + " \"%s\" " + "from index %d to %d",
                                       regex, matcher.group(), matcher.start(), matcher.end()));
               found = true;
            }
            System.out.println();
            if (!found) 
                System.out.println("Not found");
        }
    }
}
 
 
/*
run:
  
a?: Found "" from index 0 to 0

a??: Found "" from index 0 to 0

a?+: Found "" from index 0 to 0
  
*/

 

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Answer 2

package javaapplication1;
 
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class Example {
    public static void main(String[] args) {
        // X? , X?? and X?+  (X once or not at all)
        searchREGEX("a", "a?", "a??", "a?+");
    }
     
    private static void searchREGEX(String input, String... regex_list) {
        for (String regex : regex_list) {
            Pattern pattern = Pattern.compile(regex);
            Matcher matcher = pattern.matcher(input);
  
            boolean found = false;
            while (matcher.find()) {
               System.out.println(String.format("%s: Found" + " \"%s\" " + "from index %d to %d",
                                       regex, matcher.group(), matcher.start(), matcher.end()));
               found = true;
            }
            System.out.println();
            if (!found) 
                System.out.println("Not found");
        }
    }
}
 
 
/*
run:
  
a?: Found "a" from index 0 to 1
a?: Found "" from index 1 to 1

a??: Found "" from index 0 to 0
a??: Found "" from index 1 to 1

a?+: Found "a" from index 0 to 1
a?+: Found "" from index 1 to 1
  
*/

 

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Answer 3

package javaapplication1;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Example {
    public static void main(String[] args) {
        // X? , X?? and X?+  (X once or not at all)
        searchREGEX("aa", "a?", "a??", "a?+");
    }
   	
    private static void searchREGEX(String input, String... regex_list) {
	    for (String regex : regex_list) {
            Pattern pattern = Pattern.compile(regex);
            Matcher matcher = pattern.matcher(input);
 
            boolean found = false;
            while (matcher.find()) {
               System.out.println(String.format("%s: Found" + " \"%s\" " + "from index %d to %d",
                                       regex, matcher.group(), matcher.start(), matcher.end()));
               found = true;
            }
            System.out.println();
            if (!found) 
                System.out.println("Not found");
	    }
    }
}


/*
run:
 
a?: Found "a" from index 0 to 1
a?: Found "a" from index 1 to 2
a?: Found "" from index 2 to 2

a??: Found "" from index 0 to 0
a??: Found "" from index 1 to 1
a??: Found "" from index 2 to 2

a?+: Found "a" from index 0 to 1
a?+: Found "a" from index 1 to 2
a?+: Found "" from index 2 to 2
 
*/

 

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Answer 4

package javaapplication1;
 
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class Example {
    public static void main(String[] args) {
        // X? , X?? and X?+  (X once or not at all)
        searchREGEX("ba", "a?", "a??", "a?+");
    }
     
    private static void searchREGEX(String input, String... regex_list) {
        for (String regex : regex_list) {
            Pattern pattern = Pattern.compile(regex);
            Matcher matcher = pattern.matcher(input);
  
            boolean found = false;
            while (matcher.find()) {
               System.out.println(String.format("%s: Found" + " \"%s\" " + "from index %d to %d",
                                       regex, matcher.group(), matcher.start(), matcher.end()));
               found = true;
            }
            System.out.println();
            if (!found) 
                System.out.println("Not found");
        }
    }
}
 
 
/*
run:
  
a?: Found "" from index 0 to 0
a?: Found "a" from index 1 to 2
a?: Found "" from index 2 to 2

a??: Found "" from index 0 to 0
a??: Found "" from index 1 to 1
a??: Found "" from index 2 to 2

a?+: Found "" from index 0 to 0
a?+: Found "a" from index 1 to 2
a?+: Found "" from index 2 to 2
  
*/

 

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Answer 5

package javaapplication1;
  
import java.util.regex.Matcher;
import java.util.regex.Pattern;
  
public class Example {
    public static void main(String[] args) {
        // X? , X?? and X?+  (X once or not at all)
        searchREGEX("b", "a?", "a??", "a?+");
    }
      
    private static void searchREGEX(String input, String... regex_list) {
        for (String regex : regex_list) {
            Pattern pattern = Pattern.compile(regex);
            Matcher matcher = pattern.matcher(input);
   
            boolean found = false;
            while (matcher.find()) {
               System.out.println(String.format("%s: Found" + " \"%s\" " + "from index %d to %d",
                                       regex, matcher.group(), matcher.start(), matcher.end()));
               found = true;
            }
            System.out.println();
            if (!found) 
                System.out.println("Not found");
        }
    }
}
  
  
/*
run:
   
a?: Found "" from index 0 to 0
a?: Found "" from index 1 to 1

a??: Found "" from index 0 to 0
a??: Found "" from index 1 to 1

a?+: Found "" from index 0 to 0
a?+: Found "" from index 1 to 1
   
*/

 

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