用户输入不在字符串数组中的值时出错

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.

Answer 1

You can convert it into a List and use contains , eg:

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() .

Answer 2

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?

Answer 3

You could use this:-

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

Documentation Here

Answer 4

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

Answer 5

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

1. 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 } 

2. 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!");