Java random file extension generator switch statement improv

import java.util.Scanner;
import static java.lang.System.out;
import java.lang.String;
import java.util.Random;

public class mainclass {
    public static void main (String[] args){
        Scanner myScanner = new Scanner(System.in);
        Random myRandom = new Random();

        // Declaration of variables
        String input;
        int randomNumber;
        String extension = null;

        // Begin program run
        System.out.println("Welcome to the random file extension generator.");
        System.out.println("Please enter your string of text to have an extension added.");
        // User input
        input = myScanner.nextLine();
        // End user input
        randomNumber = myRandom.nextInt(11);
        if(randomNumber == 0){
            randomNumber = randomNumber + 1;
        }

        // Random extension generation

        switch (randomNumber) {
            case 1: extension =  ".png";
            break;

            case 2: extension = ".txt";
            break;

            case 3: extension = ".avi";
            break;

            case 4: extension = ".docx";
            break;

            case 5: extension = ".jpg";
            break;

            case 6: extension = ".html";
            break;

            case 7: extension = ".class";
            break;

            case 8: extension = ".wmv";
            break;

            case 9: extension = ".exe";
            break;

            case 10: extension = ".sys";
            break;

            default: System.out.println("The random number generator has encountered an error. Please restart the program. (Error: Invalid random value produced)");
        }
        // End random extension generation

        System.out.println("Thank you. Your string with the random extension added is:");
        System.out.print(input + extension);
    }
}