I was wondering how to check user input that was previously stored in an arraylist.
For example, I am asking a user to enter in letters for which i store into an arraylist. I need to make sure they don't guess the same letter again but I am not sure how. Any tips are appreciated.
Scanner scan = new Scanner(System.in);
ArrayList<String>guesses=new ArrayList<String>();
System.out.println("Enter a letter");
String userInput = scan.next();
guesses.add(userInput);
That functionality would work better with a HashSet, since searching for an existing value in a HashSet is faster than in an ArrayList.
Scanner scan = new Scanner(System.in);
Set<String> guesses=new HashSet<String>();
System.out.println("Enter a letter");
String userInput = scan.next();
if (guesses.contains(userInput)) {
// the user repeated a guess
} else {
guesses.add(userInput);
}
Of course, if you only accept one character at a time, you can use a simple array to find if a guess is repeated :
Scanner scan = new Scanner(System.in);
boolean[] guesses=new boolean[26];
System.out.println("Enter a letter");
String userInput = scan.next();
char c = userInput.charAt(0);
if (c >= 'a' && c <= 'z' && !guesses[c-'a']) {
guesses[c-'a']=true;
// this is a valid guess
} else {
// this is an invalid guess
}
If you don't want any duplicates then I would suggest that you use a HashSet. To see if the guess was previously done, just call the contains() method.
if (!guesses.contains(userInput)) {
guesses.add(userInput);
} else {
...
}
Set is that it tells you if it could add the item to the set or not, so you can use if (!guesses.add(userInput)) { /* already in the set */ } instead. But your answer is still correct.Firstly, as a good practice you should always code to an interface thus:
ArrayList<String>guesses=new ArrayList<String>();
should be changed to:
List<String>guesses=new ArrayList<String>();
Now coming back to your question, there are two options:
instead of List use Set, as it avoids duplicates, you can be sure to have unique values (recommended)
after every input execute
if (!guesses.contains(userInput))
guesses.add(userInput);
else
// if you want you can intimate the user of a duplicate value
