JAVA: check a string if there is a special character in it

Question

How do you check a string if there is a special character like: [,],{,},{,),*,|,:,>,etc.?

Answer 1

What do you exactly call "special character" ? If you mean something like "anything that is not alphanumeric" you can use org.apache.commons.lang.StringUtils class (methods IsAlpha/IsNumeric/IsWhitespace/IsAsciiPrintable).

If it is not so trivial, you can use a regex that defines the exact character list you accept and match the string against it.

Answer 2

All depends on exactly what you mean by "special". In a regex you can specify

• \W to mean non-alpahnumeric
• \p{Punct} to mean punctuation characters

I suspect that the latter is what you mean. But if not use a [] list to specify exactly what you want.

Answer 3

Have a look at the java.lang.Character class. It has some test methods and you may find one that fits your needs.

Examples: Character.isSpaceChar(c) or !Character.isJavaLetter(c)

Answer 4

Visit each character in the string to see if that character is in a blacklist of special characters; this is O(n*m).

The pseudo-code is:

for each char in string:
  if char in blacklist:
    ...

The complexity can be slightly improved by sorting the blacklist so that you can early-exit each check. However, the string find function is probably native code, so this optimisation - which would be in Java byte-code - could well be slower.

Answer 5

First you have to exhaustively identify the special characters that you want to check.

Then you can write a regular expression and use

public boolean matches(String regex)

Answer 6

Pattern p = Pattern.compile("/[^a-z0-9 ]/gi");
Matcher m = p.matcher("I am a string");
boolean b = m.matches();

if (b == true)
   System.out.println("There is a special character in my string");

Answer 7

can you explain me about that pattern class