How to Remove Special Characters from String in Java?

A character which is not an alphabet or numeric character is called a special character. We should remove all the special characters from the string so that we can read the string clearly and fluently. Special characters are not readable, so it would be good to remove them before reading.

Using Java String.replaceAll() Method

Java replaceAll() method of String class replaces each substring of this string that matches the given regular expression with the replacement.

Syntax

This method accepts two parameters:

• regex: It is the regular expression to which string is to be matched. It may be of different types.
• replacement: The string to be substituted for the match.

It returns the resultant String. It throws PatternSyntaxException if the regular expression syntax is invalid. The above method yields the same result as the expression:

Java Program to Remove Special Character

In the following example, the removeAll() method removes all the special characters from the string and puts a space in place of them.

RemoveSpecialCharacterExample1.java

Output

 This string contains special characters 

Example

In the following example, we are replacing all the special character with the space.

RemoveSpecialCharacterExample2.java

Output

 Hello Java Programmer ! 

Using User Defined Logic

In the following example, we are defining logic to remove special characters from a string. We know that the ASCII value of capital letter alphabets starts from 65 to 90 (A-Z) and the ASCII value of small letter alphabet starts from 97 to 122 (a-z). Each character compare with their corresponding ASCII value. If both the specified condition returns true it return true else return false. The for loop executes till the length of the string. When the string reaches its size, it terminates execution and we get the resultant string.

RemoveSpecialCharacterExample3.java

Output

 String after removing special characters: ProgrammingLanguage 

Using Character.isLetter() with StringBuilder

Using Character.isLetter() in combination with StringBuilder provides an efficient way to filter out non-alphabetic characters from a string in Java. The approach leverages the ability of Character.isLetter() to identify letters and the mutability of StringBuilder to construct the cleaned string dynamically.

Step 1: Create a String variable originalString and initialize it with "Hello@# World$%^&*()_+123!" and also create a StringBuilder object cleanedString to store the resulting string.

Step 2: Convert the originalString to a character array using toCharArray() and use an enhanced for Loop to iterate through each character in the character array.

Step 3: For each character c in the character array:

• Use isLetter(c) to check if c is a letter.
• If c is a letter, append it to cleanedString using append(c).

Step 4: Convert the StringBuilder object cleanedString to a String using toString() and Print the resulting string.

Let's implement the above logic in a Java program.

UsingCharater.java

Output:

 HelloWorld 

Without Using Built-in Methods

In scenarios where using built-in methods is restricted or to gain a deeper understanding of character processing, we can manually filter alphabetic characters from a string by directly comparing their ASCII values. This approach ensures control over each step of the character validation process.

Algorithm

Step 1: Create a String variable originalString and initialize it with "Hello@# World$%^&*()_+123!" and also create a StringBuilder object cleanedString to store the resulting string.

Step 2: Use a for Loop to iterate through each character in the originalString by its index.

Step 3: For each character at the current index in the Loop:

• Retrieve the character using char c = originalString.charAt(i).
• Check if the character c is a letter by comparing its ASCII value:
  • Check if c is an uppercase letter (c >= 'A' && c <= 'Z').
  • Check if c is a lowercase letter (c >= 'a' && c <= 'z').
• If c is a letter, append it to cleanedString.

Step 4: Convert the StringBuilder object cleanedString to a String using toString().

WithoutBuiltin.java

Output:

 HelloWorld 

Using Regex in Java

In Java, regular expressions (regex) offer a robust solution for string processing tasks. Previously, we utilized the replaceAll() method to eliminate special characters from strings, a task that can also be achieved through regex. With regex, the replaceAll() method utilizes the '^' character to select all characters except those specified, enabling precise removal or replacement operations.

Algorithm

Step 1: Create a String variable originalString and initialize it with "Hello@# World$%^&*()_+123!".

Step 2: Use the replaceAll method of the String class to replace all non-alphabetic characters in originalString with an empty string. The regex pattern [^a-zA-Z] is used to match any character that is not a letter.

Step 3: Store the result of the replaceAll method in a new String variable cleanedString and print the value of cleanedString.

UsingRegex.java

Output:

 HelloWorld