很抱歉提出这样一个问题，但我无法理解为什么下面的代码不能正常工作。
正如标题中所写，用户应该为代码输入一个整数，以检查它是否为素数。如果不是，则用户可以输入另一个int，但最多输入5次。
我认为素性检查是有效的，但困扰我的是递归，因为它打印出来太多时，首先给一个非素数，然后素数。
我希望有人能向我解释为什么会这样……：）
代码如下：

import java.util.Scanner;

public class Task6v5 {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        System.out.println("Enter an int: ");
        int a = scan.nextInt();
        int counter = 0;

        isPrime(a, counter, scan);

    }

    public static void isPrime(int a, int counter, Scanner scan) {

        boolean prime;

        do {

            if (a <= 1) {
                counter = counter + 1;
                System.out.println("Int to small. Enter a bigger one." 
                        + " Counter: " + counter);
                a = scan.nextInt();
                isPrime(a, counter, scan);
            } else if (a == 2) {
                prime = true;
            } else if (a % 2 == 0) {
                counter = counter + 1;
                System.out.println("This int is even, "
                        + "but not a 2. "
                        + "Enter an other int."
                        + " Counter: " + counter);
                a = scan.nextInt();
                isPrime(a, counter, scan);
            }

            for (int i = 2; i <= Math.sqrt(a); i++) {
                if (a % i == 0) {
                    //System.out.println("Are we there?");
                    //isPrime = false;
                    counter = counter + 1;
                    System.out.println("This int is not a prime. "
                            + "Enter an other int. Counter: " + counter);
                    a = scan.nextInt();
                    isPrime(a, counter, scan);
                }
            }
            prime = true;
            System.out.println("This is a prime.");

        } while (counter <= 5 && prime == false);

    }
}

我得到这个输出，例如：

Enter an int: 
1
Int to small. Enter a bigger one. Counter: 1
4
This int is even, but not a 2. Enter an other int. Counter: 2
5
This is a prime.
This is a prime.
This int is not a prime. Enter an other int. Counter: 2