JAVA EE: How to use any character, digit and non-digit Regex meta-characters

Tuesday 28 November 2017

How to use any character, digit and non-digit Regex meta-characters | Java Regex

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How to use any character, digit and non-digit Regex meta-characters | Java Regex

RegexDemo1.java

import java.util.regex.Pattern;

/**
 * 
 * \d = Any digits, short of [0-9]
 *
 */

public class RegexDemo1
{
    public static void main(String[] args)
    {
        System.out.println("metacharacters d");
        
        /*
         * Parameters:
         * 
         * regex - The expression to be compiled
         * 
         * input - The character sequence to be matched
         * 
         * Returns:
         * 
         * whether or not the regular expression matches on the input
         * 
         */
        
        System.out.println(Pattern.matches("\\d", "9"));//true (digit and comes once)
        System.out.println(Pattern.matches("\\d", "dfg"));//false (non-digit)  
        System.out.println(Pattern.matches("\\d", "8888"));//false (digit but comes more than once)  
        System.out.println(Pattern.matches("\\d", "555abc"));//false (digit and char)  
        
        System.out.println("----------------------------------");
        
        System.out.println("metacharacters d with quantifier....");  
        System.out.println(Pattern.matches("\\d*", "56565"));//true (digit may come 0 or more times)
    }

}

Output

metacharacters d
true
false
false
false
----------------------------------
metacharacters d with quantifier....
true

RegexDemo2.java

import java.util.regex.Pattern;

/**
 * 
 * \D = Any non-digit, short for [^0-9]
 *
 */
public class RegexDemo2
{
    public static void main(String[] args)
    {
        System.out.println("metacharacters D..");  
        /*
         * Parameters:
         * 
         * regex - The expression to be compiled
         * 
         * input - The character sequence to be matched
         * 
         * Returns:
         * 
         * whether or not the regular expression matches on the input
         * 
         */
        System.out.println(Pattern.matches("\\D", "m"));//true (non-digit and comes once)
        System.out.println(Pattern.matches("\\D", "xds"));//false (non-digit but comes more than once)  
        System.out.println(Pattern.matches("\\D", "1"));//false (digit)  
        System.out.println(Pattern.matches("\\D", "8989"));//false (digit)  
        System.out.println(Pattern.matches("\\D", "121abc"));//false (digit and char)  
        
        System.out.println("----------------------------------");
        
        System.out.println("metacharacters D with quantifier....");  
        System.out.println(Pattern.matches("\\D*", "peter"));//true (non-digit and may come 0 or more times)  
          
    }

}

Output

metacharacters D..
true
false
false
false
false
----------------------------------
metacharacters D with quantifier....
true

RegexDemo3.java

import java.util.regex.Pattern;

/**
 * 
 *  . = Any character (may or may not match terminator)
 *
 */
public class RegexDemo3
{
    public static void main(String[] args)
    {
        /*
         * Parameters:
         * 
         * regex - The expression to be compiled
         * 
         * input - The character sequence to be matched
         * 
         * Returns:
         * 
         * whether or not the regular expression matches on the input
         * 
         */
        System.out.println(Pattern.matches(".", "m"));//true [char and comes once]
        System.out.println(Pattern.matches(".", "8"));//true [char and comes once]
        System.out.println(Pattern.matches(".", "99"));//false [char but comes more than once]
        System.out.println(Pattern.matches(".", "uiui"));//false [char but comes more than once]
          
    }

}