如何检查字符串是否等于有效字符之一？ （国际象棋棋盘）

Question

So I want to check if the entered position is valid in Chess Board,

//returns true if the position is in the range of A1-H8

private boolean isValid(String position){
    char first=position.charAt(0);
    String letter=(""+first).toLowerCase();
    boolean validLetter=position.equals("a") || position.equals("b") || position.equals("c")|| 
            position.equals("d") || position.equals("e")|| position.equals("f") || position.equals("g") ||
            position.equals("h");

As you can see the boolean is pretty ugly, so what is a better way of doing this?

By the way, how do you check if the second character is a number??

===edit==== Thanks everyone! But all your answers seem so complicated to me and I just start learning java, so would you please give me a more fundamental approach to the problem?

Answer 1

A regular expression makes short work of this is one:

private boolean isValid(String position) {
    return position.matches("^[a-h][1-8]$");
}

If you you're not comfortable with regexes, maybe something like this will suit you better:

private boolean isValid(String position) {
    if (position.length() != 2) {
        return false;
    }
    char firstChar = position.charAt(0);
    List<Character> validFirstChars = Arrays.asList('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h');
    if (!validFirstChars.contains(firstChar)) {
        return false;
    }
    char secondChar = position.charAt(1);
    List<Character> validSecondChars = Arrays.asList('1', '2', '3', '4', '5', '6', '7', '8');
    if (!validSecondChars.contains(secondChar)) {
        return false;
    }
    return true;
}

As an optimization, validFirstChars and validSecondChars could be made final static members of the class instead of instantiated on each method invocation.

Answer 2

Characters are really integers in Java, which can be used to check if a character falls within a certain range. So you can check if the character falls within the range 97 to 104 (which is the values of 'a' to 'h' in ascii ):

return first < 105 && first > 96;

(You can read more about characters on my page here :)

Answer 3

A really simple example :

private boolean isValid(String position) {
  // We will check only strings with 2 characters
  if (position.length() != 2) {
    return false;
  }
  // If the first char is not between a and h, let's return false.
  char first = position.charAt(0);
  if (first < 'a' || 'h' < first) {
    return false;
  }
  // If the second char is not between 1 and 8, let's return false.
  char second = position.charAt(1);
  if (second < '1' || '8' < second) {
    return false;
  }
  // We couldn't prove the position was invalid, so it must be valid.
  return true;
}