Checking if a character is a special character in Java

Question

Possible Duplicate    JAVA  check a string if there is a special character in it       I am a novice programmer and am looking for help determining if a character is a special character  My program asks the user to input the name of a file  and the program reads the text in the file and determines how many blanks spaces  digits  letters  and special characters are in the text  I have the code completed to determine the blanks  digits  and letters  however am unsure of how to check if a character is a special character  Any help you can offer is appreciated and if something was not clear enough I can try to elaborate  My code so far is    import java util Scanner  import java io     public class TextFile   public static void main String   args      Scanner input   new Scanner  System in     String fileName    boolean goodName   false    int blankCount   0    int letterCount   0    int digitCount   0    int specialcharCount   0    String currentLine    char c    Scanner lineFile  null    FileReader infile     System out println  Please enter the name of the file        fileName   input nextLine       while   goodName        try        infile   new FileReader fileName         lineFile   new Scanner infile          goodName  true            catch IOException e          System out println  Invalid file name  please enter correct file name            fileName input nextLine                 while  lineFile hasNextLine         currentLine   lineFile nextLine        for int j 0  j lt currentLine length   j           c currentLine charAt j         if c        blankCount          if Character isDigit c   digitCount          if Character isLetter c   letterCount          if   specialcharCount                    I need something to put in the if statement at the end to increment specialcharCount

User · Answer

This method checks if a String contains a special character (based on your definition).

/**
 *  Returns true if s contains any character other than 
 *  letters, numbers, or spaces.  Returns false otherwise.
 */

public boolean containsSpecialCharacter(String s) {
    return (s == null) ? false : s.matches("[^A-Za-z0-9 ]");
}

You can use the same logic to count special characters in a string like this:

/**
 *  Counts the number of special characters in s.
 */

 public int getSpecialCharacterCount(String s) {
     if (s == null || s.trim().isEmpty()) {
         return 0;
     }
     int theCount = 0;
     for (int i = 0; i < s.length(); i++) {
         if (s.substring(i, 1).matches("[^A-Za-z0-9 ]")) {
             theCount++;
         }
     }
     return theCount;
 }

Another approach is to put all the special chars in a String and use String.contains:

/**
 *  Counts the number of special characters in s.
 */

 public int getSpecialCharacterCount(String s) {
     if (s == null || s.trim().isEmpty()) {
         return 0;
     }
     int theCount = 0;
     String specialChars = "/*!@#$%^&*()\"{}_[]|\\?/<>,.";
     for (int i = 0; i < s.length(); i++) {
         if (specialChars.contains(s.substring(i, 1))) {
             theCount++;
         }
     }
     return theCount;
 }

NOTE: You must escape the backslash and " character with a backslashes.

The above are examples of how to approach this problem in general.

For your exact problem as stated in the question, the answer by @LanguagesNamedAfterCoffee is the most efficient approach.

User · Answer

What I would do   char c  int cint  for int n   0  n  lt  str length    n            c   str charAt n       cint    int c      if cint  lt 48     cint  gt  57  amp  amp  cint  lt  65      cint  gt  90  amp  amp  cint  lt  97     cint  gt  122                specialCharacterCount             That is a simple way to do things  without having to import any special classes  Stick it in a method  or put it straight into the main code   ASCII chart  http   www gophoto it view php i http   i msdn microsoft com dynimg IC102418 gif  UHsqxFEmG08

User · Answer

You can use regular expressions   String input       if  input matches    a-zA-Z0-9        If your definition of a  special character  is simply anything that doesn t apply to your other filters that you already have  then you can simply add an else  Also note that you have to use else if in this case   if c               blankCount      else if  Character isDigit c         digitCount      else if  Character isLetter c         letterCount      else      specialcharCount

User · Answer

Take a look at class java lang Character static member methods  isDigit  isLetter  isLowerCase        Example   String str    Hello World 123      int specials   0  digits   0  letters   0  spaces   0  for  int i   0  i  lt  str length      i       char ch   str charAt i      if   Character isDigit ch   amp  amp   Character isLetter ch   amp  amp   Character isSpace ch             specials       else if  Character isDigit ch             digits       else if  Character isSpace ch             spaces       else           letters

[java] Checking if a character is a special character in Java

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