Error when the user enters values not in String Array

Question

String[] alpha = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"};

I have made the Array above including all the letters in the alphabet for a letter guessing game.

I am not sure how I could get an error message to appear if the user enters something outside of these values of the alphabet eg. a number? Any help would be greatly appreciated.

regex? like `if(value.equals("\\d"))` --> error. or even easier, vonvert the array to a list and perform a check like this: `if(!list.contains(value))` -->error — XtremeBaumer, Apr 19 '17 at 13:25
`!input.matches("[a-z]")` should work... Forget the array of the alphabet — OneCricketeer, Apr 19 '17 at 13:27

score 4 · Answer 1 · answered Apr 19 '17 at 13:26

4

You can convert it into a List and use contains, e.g.:

String[] alpha = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"};
List<String> list = Arrays.asList(alpha);
System.out.println(list.contains("a"))

If you want case insensitive comparison then you can use toLowerCase().

answered Apr 19 '17 at 13:26

Darshan Mehta

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This has worked in giving me the error, although it is outputting 26 errors when i try input a number, would you know how this could be fixed? Thanks for the help! – java1234 Apr 20 '17 at 12:54
Can you add an example? – Darshan Mehta Apr 20 '17 at 12:56
Is the line of code System.out.println(list.contains("a")) needed? I have tried an if statement instead which could be causing the repeated error messages. if(!list.contains(guess)){ System.out.println("Out of range"); – java1234 Apr 20 '17 at 13:02
`if(!list.contains(guess))` should work as long as `guess` is a String. – Darshan Mehta Apr 20 '17 at 13:24

score 1 · Answer 2 · edited May 23 '17 at 10:31

1

You could use a character array than that one . Example is given here https://www.javatpoint.com/java-string-tochararray. Then you could use indexof method to see if the user entered value is valid as explained here How can I check if a single character appears in a string?

edited May 23 '17 at 10:31

Community

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answered Apr 19 '17 at 13:29

Nobody

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score 1 · Answer 3 · answered Apr 19 '17 at 13:29

1

You could use this:-

if (! ArrayUtils.contains( alpha, "[i-dont-exist]" ) ) {
    try{
        throw new Exception("Not Found !");
    }catch(Exception e){}
}

Documentation Here

answered Apr 19 '17 at 13:29

Tilak Madichetti

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score 1 · Answer 4 · answered Apr 19 '17 at 13:31

if the purpose to check the existence of the elements inside collections its more reasonable to use a set since the access time is constanct

so Instead

   Set<String> set = new HashSet<>();//if not java 8 make it HashSet<String>
   set.put("a") // do this for all the strings you would like to check

Then to check if a string exists in this set

if(set.contains(str)) //str is the string you want to make sure it exists in the collections

score 0 · Answer 5 · answered Apr 19 '17 at 13:52

Use this approach if you would like to stick with array instead of other data structures.

Create a method that return true if the user input is present in the array, otherwise return false

public static boolean isValid(String input) {
    String[] alpha = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", 
        "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", 
        "w", "x", "y", "z"};

    for(String s: alpha) {
        if(input.equals(s)) {  //use input.equalsIgnoreCase(s) for case insensitive comparison
            return true;    //user input is valid
        }
    }

    return false;   //user input is not valid
}

In the calling method, simply pass the user input to isValid

//write some codes here to receive user input.....

if(!isValid(input))
    System.out.println("Oops, you have entered invalid input!");

Error when the user enters values not in String Array

5 Answers5