Question

What is wrong with the following Java Code.

public class TestEdible
{
    abstract class Animal
    {
        /** Return animal sound */
        public abstract String sound();
    }

    class Chicken extends Animal implements Edible
    {
        @Override
        public String howToEat()
        {
            return "Chicken: Fry it";
        }

        @Override
        public String sound()
        {
            return "Chicken: cock-a-doodle-doo";
        }
    }

    class Tiger extends Animal
    {
        @Override
        public String sound()
        {
            return "Tiger: RROOAARR";
        }
    }

    abstract class Fruit implements Edible
    {
        // Data fields, constructors, and methods omitted here
    }

    class Apple extends Fruit
    {
        @Override
        public String howToEat()
        {
            return "Apple: Make apple cider";
        }
    }

    class Orange extends Fruit
    {
        @Override
        public String howToEat()
        {
            return "Orange: Make orange juice";
        }
    }

    public static void main(String[] args)
    {
        Object[] objects = {new Tiger(), new Chicken(), new Apple()};
        for (int i = 0; i < objects.length; i++)
        {
            if (objects[i] instanceof Edible)
            {
                System.out.println(((Edible)objects[i]).howToEat());
            }

            if (objects[i] instanceof Animal)
            {
                System.out.println(((Animal)objects[i]).sound());
            }
        }
    }
}

The error occurs at the line:

Object[] objects = {new Tiger(), new Chicken(), new Apple()};

With the message:

Error:(58, 29) java: non-static variable this cannot be referenced from a static context

Error:(58, 42) java: non-static variable this cannot be referenced from a static context

Error:(58, 57) java: non-static variable this cannot be referenced from a static context

The code is from "Introduction to a Java Programming 9th Edition"

Answer 1

Hey, I have given my best to solve your query and with a proper explanation, if you have still any doubt feel free to comment and if my solution was helpful then leave a like.

I can understand your frustration and this is very common when you start learning a new programming language nowhere you won't believe how small was the correction and that small correction was stopping you from the solution.

It was all because of a parenthesis { }. I know you must be wondering what I am saying just look at the snapshot I have added.

Inside the class, TestEdible just keep your main method and then close that class and the rest of the code will be outside of class TestEdible like this

// image

U ĐWNE 2. public class TestEdible { public static void main(String[] args) { Object[] objects = {new Tiger(), new Chicken(), new Apple() }; for (int i = 0; i < objects.length; i++) { if (objects[i] FILL_CODE_OR_CLICK_ANSWER Edible) System.out.println(((Edible)objects[i]).howToEat()); if (objects[i] instanceof Animal) { System.out.println(((Animal)objects[i]).sound()); } } 13 14 15 16 17 18 19 abstract class Animal { /** Return animal sound */ public abstract String sound(); } 2e 22 21. class Chicken extends Animal implements Edible { @Override public String howToEat() { 24 return "Chicken: Fry it"; 23 - 26 27 @Override public String sound() { return "Chicken: cock-a-doodle-doo";

// image

30 31 } } 33 - class Tiger extends Animal { 34 @Override public String sound() { 36 return "Tiger: RROOAARR"; 37 } 38 } 35 40 abstract class Fruit implements Edible { 41 // Data fields, constructors, and methods omitted here 42 } 43 46 44 - class Apple extends Fruit { @Override public String howToEat() { 47 return "Apple: Make apple cider"; 48 49 } 52 51 class Orange extends Fruit { @Override 53 public String howToEat() { 54 return "Orange: Make orange juice"; 55 } 56 } 57

and check now you will get your expected output something like this

ODK8>javac TestEdible.java Compiled successful UDK8>java TestEdible Tiger: RROOAARR Chicken: Fry it Chicken: cock-a-doodle-doo Apple: Make apple cider

Now let me tell you the concept behind this problem and what your error actually means.

It is a simple concept of static as you must know that we cannot make a reference to a non-static method from a static method and your main method is static. This concept will irritate you for a while in the beginning but you must know the difference between static and nonstatic.

Static Variables belongs to the class and its value will always remain the same for all instance and when a class is loaded into JVM a static variable gets initialized and see the main method do we need to create any instance to reference it through any variable no because it is static.

We need to create an instance of the class as an object and then only we will be able to access methods and any variables of that class that are not declared static. Once our java program starts with the main function we can access any variable having modifier static as they exist as part of the class. Then for those variables and methods of the class which are not static and outside of the main method will not be used until we create an instance of the class as an object within the main method.