Check if a String Contains a Special Character in Java

Problem: Write a Java program to check whether a given string contains a special character or not.

Example:

Input:  pencil@programmer
Output: String has Special Character

Input:   Pencil Programmer
Output:  String has No Special Character

So let’s see how we can do that in Java.

Method 1: Using Java Regex

The Java Regex or regular expression is a pattern (sequence of characters) that helps in the search or manipulation of strings.

We usually define a regex pattern in the form of a string, for example “[^A-Za-z0-9 ]” and use a matcher in Java to match the pattern in a particular string.

“[A-Za-z0-9 ]” will match strings made up of alphanumeric characters only (blank space inclusive).

“[^A-Za-z0-9 ]” will match strings made up of characters other than alphanumeric and blank spaces i.e. special characters.

So if the input string matches the “[^A-Za-z0-9 ]” pattern it means it contains at least one character.

Let’s implement the same in Java and check whether a string contains a special character or not:

//import Pattern and Matcher classes from java.util package
import java.util.regex.Pattern;
import java.util.regex.Matcher;
import java.util.Scanner;
 
public class Main
{
	public static void main(String[] args) {
	Scanner in=new Scanner(System.in);
	    
        System.out.println("Enter a String");
	String str = in.nextLine();
		
	//Specify the pattern and get matcher
	Pattern p = Pattern.compile("[^A-Za-z0-9 ]");
        Matcher m = p.matcher(str);
        
        if(m.find())
            System.out.println("String contains Special Characters");
        else
            System.out.println("String doesn't have any Special Characters");
	}
}

Output:

Note: The [^A-Za-z0-9] pattern will return true if a string contains a blank space, therefore we have modified the pattern to [^A-Za-z0-9 ] to exclude the blank space from the check criteria.

Method 2: Using Brute Force

In this method, we specify all possible special characters into a single string, then match each of them in the input string.

For this, we use the inbuilt contain() method of string class.

import java.util.Scanner;
 
public class Main
{
	public static void main(String[] args) {
	Scanner in=new Scanner(System.in);
	    
	System.out.println("Enter a String");
	String str = in.nextLine();
		
	//Specify all posible special charcters
	String specialCharacters=" !#$%&'()*+,-./:;<=>?@[]^_`{|}";
		
	boolean found = false;
		
	for(int i=0; i<specialCharacters.length(); i++){
		    
	    //Checking if the input string contain any of the specified Characters
	    if(str.contains(Character.toString(specialCharacters.charAt(i)))){
	        found = true;
	        System.out.println("String contains Special Characters");
	        break;
	    }
	}
	
        if(found == false)
            System.out.println("String doesn't have any Special Characters");
           
       }
}

Output:

These are the two methods using which we can easily check for special characters in the Java string.