How to insist that a users input is an int?

Question

Basic problem here.. I will start off by asking that you please not respond with any code, as that likely will only confuse me further (programming noob). I am looking for

Answer 1

public class Sample {

/**
 * author CLRZ
 */
public static void main(String[] args) {
    int a; // variable
    Scanner in = new Scanner(System.in); // scans your input
    System.out.println("Enter your number's choice:"); 
    int sem1 = in.nextInt(); // reads next integer
    if (sem1 == 1) // conditioned if your choice number is equal to 1
    System.out.println("Hello World1"); // output wil be Hello World
    int b;

    System.out.println("Enter your number's choice:");
    int sem2 = in.nextInt(); 
    if (sem2 == 2)
    System.out.println("Hello World2");
    int c;

    System.out.println("Enter your number's choice:");
    int sem3 = in.nextInt(); 
    if (sem3 == 3)
    System.out.println("Hello World3");
}

}