How can I incorporate functions and methods into my if-else conditions in Java?

I am able to run a program that calculates the perimeter of a shape and uses if-else conditions to determine what shape it is. However, I am struggling to pair my if-else conditions with functions and methods.

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int sideA;
    int sideB;
    int sideC;
    int sideD;
    int perimeter = 0;

    System.out.println("Enter side 1: ");
    sideA = scan.nextInt();

    System.out.println("Enter side 2: ");
    sideB = scan.nextInt();

    System.out.println("Enter side 3: ");
    sideC = scan.nextInt();

    System.out.println("Enter side 4: ");
    sideD = scan.nextInt();

    System.out.println("Forms a square with a perimeter of " + perimeter);
    System.out.println("Forms a rectangle with a perimeter of " + perimeter);
    System.out.println("Does not form a rectangle or square.");
}

private static int add(int sideA, int sideB, int sideC, int sideD) {     
    int perimeter = sideA + sideB + sideC + sideD;
    return perimeter;
}

private static void isSquare(int sideA, int sideB, int sideC, int sideD, int perimeter) {
if (sideA == sideB && sideB == sideC && sideC == sideD && sideD == sideA) {
        System.out.println("Forms a square with a perimeter of " + perimeter);
    }

    else if (sideA == sideC && sideB == sideD) {
        System.out.println("Forms a rectangle with a perimeter of " + perimeter);
      }

    else if (sideA == sideB && sideC == sideD) {
        System.out.println("Forms a rectangle with a perimeter of " + perimeter);
      }

    else if (sideA == sideD && sideB == sideC) {
        System.out.println("Forms a rectangle with a perimeter of " + perimeter);
      }

    else {
        System.out.println("Does not form a rectangle or square.");
    }
}

The program I'm working on now has problems with reaching the end of its file while parsing. How do I improve that end of the file so that my program completes its parsing?