CODEWITHSUNDEEP
java
Jacob Fuchs
Jacob Fuchs

Reputation: 357

Scanner and user's inputs

Using the code below, the loop does not end when I use +, - and Q. 

String[] validOperators = {"+", "-", "/", "*", "=", "q", "Q"};
String userInput; 
Scanner scanner = new Scanner(System.in);

System.out.print("Please enter an operation (+, -, /, *, = or Q to quit): ");
userInput = scanner.nextLine();

while(Arrays.binarySearch(validOperators, userInput) <= -1) {
    System.out.print("Invalid input (+, -, /, *, = or Q to quit): ");
    userInput = scanner.nextLine();
}

Why this happens and how can I implemented with the right way?

Upvotes: 0

Views: 74

Answers (3)

Tena
Tena

Reputation: 642

I'd rather use Arrays and Streams, available since Java 8. For example :

Arrays.stream(validOperators).anyMatch(userInput::equals)

If you need a better performance solution for a small list of elements, both memory and process efficient and that doesn't use syntactic sugar or Java 8 streams (while loop is clearer and improved thanks to Vinod Singh Bist):

public static void main(String[] args) {

    char[] validOperators = {'+', '-', '/', '*', '=', 'q', 'Q'}; // String is more expensive
    char userInput;
    Scanner scanner = new Scanner(System.in);

    do{
        System.out.print("Please enter a valid operation ( +, -, /, *, = , q or Q ) to quit: ");
        userInput = scanner.next().charAt(0);
    }while(!contains(validOperators, userInput)) ;
}

private static boolean contains(char[] elements, char c) {
    // for loop is usually faster for small lists than any built-in iterator for primitives like char
    for (int i = elements.length - 1; i >= 0; i--) {
        if (elements[i] == c) {
            return true;
        }
    }
    return false;
}

Upvotes: 1

VSB
VSB

Reputation: 327

Try below mentioned solution.

    String[] validOperators = {"+", "-", "/", "*", "=", "q", "Q"};
    String userInput; 
    Scanner scanner = new Scanner(System.in);
    Arrays.sort(validOperators);

    do{
        System.out.print("Please enter a valid operation ( +, -, /, *, = , q or Q ) to quit: ");
        userInput = scanner.nextLine();
    }while(Arrays.binarySearch(validOperators, userInput) <= -1);

Upvotes: 1

Rmahajan
Rmahajan

Reputation: 1371

Arrays.binarySearch(validOperators, userInput) require sorted array.

If array is not sorted, the results are undefined. You should you Arrays.sort(validOperators);

Upvotes: 1

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