Non-Static method cannot be referenced from a static context with methods and variables [duplicate]

Question

In writing a BookStoreApplication which uses Book, Tape, and CD classes to create objects. Although unfinished, the application class should create new BookStoreItems, which are Book, Tape, and CD. They inherit from the BookStoreItems class. In this application class I keep getting the error:

error: non-static method printMenu() cannot be referenced from a static context
error: non-static method getUserChoice() cannot be referenced from a static context
error: non-static variable input cannot be referenced from a static context

I've changed it to be static and then not to be static, yet I continue to get this error...

import java.util.Scanner;

public class BookStoreApp2 {

    //constants for options
    static final int ADD_BOOK = 0;
    static final int ADD_TAPE = 1;
    static final int ADD_CD = 2;
    static final int QUIT = -1;

    Scanner input = new Scanner (System.in);

    public static void main(String[] args) {


        BookStoreItem[] item;//declaring array

        item = new BookStoreItem[10];//initializing array

        int itemType = -1;

        printMenu();
        getUserChoice();

        for (int i = 0; i < item.length; i++){
            System.out.print("\n" + i + "\tEnter 0 for Book, 1 for Tape, 2 for CD: ");
            itemType = input.nextInt();

            switch (itemType) {
                case 0:
                    item[i] = new Book();
                    break;
                case 1:
                    item[i] = new Tape();
                    break;
                case 2:
                    item[i] = new CD();
                    break;
                default: 
                    System.out.println("\nInvalid choice.");
            }//end of switch statement

        }//end of for loop

        for (int i = 0; i < item.length; i++) {
            System.out.println("\nAnimal #" + i + ": ");

            System.out.println("\n\tTitle: " + item[i].getTitle()); //polymorphic because they can operate on separate objects
            System.out.println("\n\tAuthor: " + item[i].getAuthor());
        }//end of for


    }//end of main method


//PRINT MENU----------------------------------------------------------  
    public void printMenu(){
        System.out.println("\nPress:");
        System.out.println("\t" + ADD_BOOK + "\tTo add a book to the book store.\n");
        System.out.println("\t" + ADD_TAPE + "\tTo add a tape to the book store.\n");
        System.out.println("\t" + ADD_CD + "\tTo add a CD to the book store.\n");
        System.out.println("\t" + QUIT + "\tTo exit\n");
    }
//---------------------------------------------------------------------
//GET USER CHOICE------------------------------------------------------ 
     public int getUserChoice() {
        int choice;     
        System.out.print("Please enter your choice: ");
        choice = input.nextInt();

        return choice;
    }//end of getUserChoice
//----------------------------------------------------------------------

}//end class

Answer 1

You need to make both your method - printMenu() and getUserChoice() static, as you are directly invoking them from your static main method, without creating an instance of the class, those methods are defined in. And you cannot invoke a non-static method without any reference to an instance of the class they are defined in.

Alternatively you can change the method invocation part to:

BookStoreApp2 bookStoreApp = new BookStoreApp2();
bookStoreApp.printMenu();
bookStoreApp.getUserChoice();