如何检查int是否包含字母

Question

I am trying to validate my code by error checking. I want to make sure the integer people enter does not contain a letter or more. Here is my code. I am supposed to solve this problem using a one dimensional array. I got the code working but I am having problems with adding the error checking in. Any help would be appreciated. Thanks

public void getNumbers() {
    Scanner keyboard = new Scanner(System.in);

    int array[] = new int[5];
    int count = 0;
    int entered = 0;
    int k = -1;

    while (entered < array.length) {

        System.out.print("Enter a number ");
        int number = keyboard.nextInt();

        if (10 <= number && number <= 100) {

            boolean containsNumber = false;

            entered++;

            for (int i = 0; i < count; i++) {
                if (number == array[i]) // i Or j
                {
                    containsNumber = true;
                }
            }
            if (!containsNumber) {
                array[count] = number;
                count++;
            } else {
                System.out.println(number + " has already been entered");
            }
        } else {
            System.out.println("number must be between 10 and 100");
        }

        //what does %d do?
        for (int j = 0; j < count; j++) {
            System.out.printf("%d ", array[j]);
        }
        System.out.println();

    }
}

}

Answer 1

I'm assuming that you would want your program to ask the user to re-enter a number if they do not input a number the first time. In this scenario you might want to try something along the lines of this:

Scanner sc = new Scanner(System.in);
System.out.println("Enter a number: ");
while(!sc.hasNextInt()) {
    //print some error statement
    sc.nextLine(); 
}
int number = sc.nextInt();
System.out.println("Number is: " + number); // to show the value of number
// continue using number however you wish

Since hasNextInt() returns a boolean determining whether or not the input is an Integer, the program will never leave the while-loop until the program can confirm that the user has entered an integer.

Answer 2

keyboard.nextInt() will throw a InputMismatchException if you input a String.

If you want to check whether Scanner has an integer to read, you can use keyboard.hasNextInt() .

Alternatively, you can read the input as String s = keyboard.next() which will take the input as a String, and then use s.matches(".*\\\\d+.*") to detect whether or not it is an integer.

UPDATE: To answer questions - keyboard.hasNextInt() will return a boolean. So for example, after System.out.print("Enter a number") , you could have an if statement checking to see if keyboard can receive numerical input, ie. if(keyboard.hasNextInt) . If this is true, that means the user has entered numerical input, and you could continue with saying int number = keyboard.nextInt() . If it is false, you would know that the user input is non-numerical.