Hexadecimal Color Code Regular Expression Pattern


^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$

Description


^		 #start of the line
 #		 #  must constains a "#" symbols
 (		 #  start of group #1
  [A-Fa-f0-9]{6} #    any strings in the list, with length of 6
  |		 #    ..or
  [A-Fa-f0-9]{3} #    any strings in the list, with length of 3
 )		 #  end of group #1 
$		 #end of the line

Whole combination is means, string must start with a “#” symbol , follow by a letter from “a” to “f”, “A” to “Z” or a digit from “0” to 9″ with exactly 6 or 3 length. This regular expression pattern is very useful for the Hexadecimal web colors code checking.

Java Regular Expression Example


package com.mkyong.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class HexValidator{
	
   private Pattern pattern;
   private Matcher matcher;
 
   private static final String HEX_PATTERN = "^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$";
	        
   public HexValidator(){
	  pattern = Pattern.compile(HEX_PATTERN);
   }
	  
   /**
   * Validate hex with regular expression
   * @param hex hex for validation
   * @return true valid hex, false invalid hex
   */
   public boolean validate(final String hex){
		  
	  matcher = pattern.matcher(hex);
	  return matcher.matches();
	    	    
   }
}

Hex code that match:

1. “#1f1f1F”, “#AFAFAF”,”#1AFFa1″,”#222fff”, “#F00”, “#F00”

Hex code that doesn’t match:

1. “123456” – must start with a “#” symbol
2. “#afafah” – “h” is not allow, valid letter from “a” to “f”
3. “#123abce” – either 6 length or 3 length
4. “aFaE3f” – must start with a “#” symbol, either 6 length or 3 length
5. “F00” – must start with a “#” symbol
6. “#afaf” – either 6 length or 3 length
7. “#F0h” – “h” is not allow, valid letter from “a” to “f”

Unit Test – HexValidator


package com.mkyong.regex;

import org.testng.Assert;
import org.testng.annotations.*;
 
/**
 * Hex validator Testing
 * @author mkyong
 *
 */
public class HexValidatorTest {
 
	private HexValidator hexValidator;
    
	@BeforeClass
        public void initData(){
		hexValidator = new HexValidator();
        }
    
	@DataProvider
	public Object[][] ValidHexProvider() {
		return new Object[][]{
			   {new String[] {
				"#1f1f1F", "#AFAFAF","#1AFFa1","#222fff", "#F00"
			   }}
		};
	}
	
	@DataProvider
	public Object[][] InvalidHexProvider() {
		return new Object[][]{
			{new String[] {
				   "123456","#afafah","#123abce","aFaE3f",
				   "F00","#afaf", "#F0h"	 
		        }}
		};
	}
	
	@Test(dataProvider = "ValidHexProvider")
	public void ValidHexTest(String[] hex) {
		
	   for(String temp : hex){
		   boolean valid = hexValidator.validate(temp);
		   System.out.println("Hex is valid : " + temp + " , " + valid);
		   Assert.assertEquals(true, valid);
	   }
	   
	}
	
	@Test(dataProvider = "InvalidHexProvider", dependsOnMethods="ValidHexTest")
	public void InValidHexTest(String[] hex) {
		
	   for(String temp : hex){
		   boolean valid = hexValidator.validate(temp);
		   System.out.println("Hex is valid : " + temp + " , " + valid);
		   Assert.assertEquals(false, valid);
	   }
	   
	}
}

Unit Test – Result


Hex is valid : #1f1f1F , true
Hex is valid : #AFAFAF , true
Hex is valid : #1AFFa1 , true
Hex is valid : #222fff , true
Hex is valid : #F00 , true
Hex is valid : 123456 , false
Hex is valid : #afafah , false
Hex is valid : #123abce , false
Hex is valid : aFaE3f , false
Hex is valid : F00 , false
Hex is valid : #afaf , false
Hex is valid : #F0h , false
PASSED: ValidHexTest([Ljava.lang.String;@1a626f)
PASSED: InValidHexTest([Ljava.lang.String;@e5855a)

===============================================
    com.mkyong.regex.HexValidatorTest
    Tests run: 2, Failures: 0, Skips: 0
===============================================


===============================================
mkyong
Total tests run: 2, Failures: 0, Skips: 0
===============================================

Reference

http://en.wikipedia.org/wiki/Web_colors

Want to learn more about regular expression? Highly recommend this best and classic book – “Mastering Regular Expression”