CODEWITHSUNDEEP
java
Gennadiy
Gennadiy

Reputation: 35

Please explain Java inheritance in this case

I'm learning Java and can't understand some tricks of inheritance. Example:

Questions:

1) Why Cat uses Tigers method? See below example of "make_a_sound" method. It's from Tiger, but Cat can use it.

2) Why Cat, can not see any properties of Tiger? Cat can use method "make_a_sound" of Tiger, but can not see its properties... quite strange.

Thanks, Gennadiy

public class Solution {
    public static void main(string[] args) {

        Cat cat = new Tiger();

        // The result is from Tiger class: A tiger says RRRRR & new tiger property
        // Why???
        cat.make_a_sound();

        // Only cat's and Animal's properties are visible. No Tiger's properties
        System.out.println(cat.this_is_a_cat);
    }

    // Base class
    public class Animal {
        public String this_is_an_animal = "Animal";

        public void make_a_sound() {
            System.out.Printf("I'm an animal");
        }
    }

    // Extends base class
    public class Cat extends Animal {
        public String this_is_a_Cat = "Hi, I'm a cat";

        public void make_a_sound() {
            System.out.Printf("A cat says meey");
        }
    }

    // Extends prev. class
    public class Tiger extends Cat {
        public String this_is_a_Tiger = "Tiger";

        public void make_a_sound() {
            System.out.Println("A tiger says RRRRRR");

            this_is_a_Tiger = "new tiger property";
            System.out.println(new_tiger_property);
        }
    }
}

Upvotes: 0

Views: 311

Answers (3)

garykwwong
garykwwong

Reputation: 2427

This link could give you some concept regarding Overriding in Java: https://www.geeksforgeeks.org/overriding-in-java/

For simplicity, Overriding only take effective on methods (regarding Question 1), but not on field variables (regarding Question 2).

Upvotes: 0

tarun
tarun

Reputation: 216

  1. Why Cat uses Tigers method? See below example of "make_a_sound" method. It's from Tiger, but Cat can use it.

Answer) Because when you say Cat cat = new Tiger() you are not saying any cat,you are saying you want sound of the Tiger and not any generic cat.Tiger is using cat's "make_a_sound" method by over riding the implementation by the Tigers sound.

if you had not overriden tigers "make_a_sound" method then the Cat's "make_a_sound" method will be called.You can try it out by saying super().make_a_sound in Tiger class or removing implementation of this method.

2) Why Cat, can not see any properties of Tiger? Cat can use method "make_a_sound" of Tiger, but can not see its properties... quite strange.

Answer) If parents classes would know everything about child class then OOPS will be broken.In OOPS each class should only know about what it does and nothing else.It does not care of other class responsibility.

Upvotes: 0

Always Learning
Always Learning

Reputation: 5601

You defined cat as type Cat. That means cat can do anything that any other Cat can do. The Animal object does define the make_a_sound function so it's available to all Animal instances. When you run your code, the variable cat points to a Tiger instance so when make_a_sound is called, it's the one in Tiger that runs. That's the whole point of inheritance.

For your second question, cat is of type Cat so you can only do things with it that you can do with any Cat object. Since this_is_a_Tiger is not something every Cat object has, it is not available to cat even though cat really points to a Tiger.

But you could do this:

if (cat instanceof Tiger) {
   Tiger tiger = (Tiger)cat;
   System.out.println(tiger.this_is_a_Tiger);
}

Upvotes: 1

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