如何在java中声明可以存储超类和子类对象的数组？

Question

I am trying to figure out how to create an array that can store super class and subclass objects.

   Book[] books = new Book[10]

Do i have to use the keyword super or sub ? please clear my doubt.

Thank you

Answer 1

Let's assume Book is your super class and then your sub class is ->

Class SuspenseBook extends Book {
//code...
}

Now your array,

Book[] books = new Book[10]

can store objects of Book as well as SuspenseBook objects.

Let me know if this helps.

Answer 2

Yes you can store Subclass object inside a super class array of objects. Lets say you have this piece of code:

class Animal {
    void saySomething() {System.out.print(" Hummmmm!");}
}

class Cow extends Animal {
    protected void saySomething() {System.out.print(" oMooo!");}
}
public class test {
    public static void main(String [] args) {
        System.out.print(" MooYa!");
        Animal [] animals = {new Animal(), new Cow()};
        for( Animal a : animals) {
            a.saySomething();
        }
    }
}

This particular piece of code has Animal[] animals = { new Animal(), new Cow()} on line number 11. This code will create an array of the superclass type (ie Animal ) and will initialize two objects - one of the superclass and one of the subclass to be stored in the array. Now since the subclass Cow inherits the superclass Animal therefore adding the Cow class object to the superclass array could be re-written as : Animal animals = new Cow(); This is polymorphism where a superclass reference variable can used to store the address of a subclass object. In short the superclass can take forms of the subclass( book definition).

**Thus to answer you question you can store subclass object inside a superclass array.