Is the type of member class defined by the reference variable or what it points to ?

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in the example below when i call the foo method with p it gets the one in child class but when i access the num variable it gets the one in parent class, so is the member type based on the reference variable type or what object it points to ?

Java

public class Main {

    public static void main(String[] args) {
    Parent p=new Child();
        System.out.println(p.num);
        p.foo();

    }

}


class Parent {
    public int num = 10;

    void foo() {
        System.out.println("Foo in parent");
    }
}


class Child extends Parent {
    public int num = 100;
    @Override
    void foo() {
        System.out.println("Foo in Child");
    }
}

What I have tried:

i don't what to fill in here so this is just random, sorry !

Posted 19-Apr-19 9:15am

hiwa doski

Updated 19-Apr-19 9:33am

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Gerry Schmitz · Accepted Answer · 2019-04-19T09:33:00

Solution 1

You got an "override" for foo; but not num; and child is cast as a "parent"; so it goes for parent.num.

Those are the differences.

Posted 19-Apr-19 9:33am

Gerry Schmitz

Comments

hiwa doski 19-Apr-19 15:44pm

okay thanks, but another question let's say child class contains method bar() if the reference variable of parent class point to the child object, and that child object contain the bar() method then why we can't call it with parent reference?

[no name] 19-Apr-19 19:06pm

By "casting" child to parent, you limit child to only the members of "parent". It's a "contract" saying this object will at least support ONLY parent behavior, and nothing else (and the "compiler" respects this, even though we may sometimes be able to trick it).

While cast as parent, it's still a "child" after all and can (apparently) bring the override into play.

The override makes sense when you consider that a parent method can be virtual or abstract (i.e. a "stub") and the override must be honored to avoid a "not implemented" exception.

hiwa doski 24-Apr-19 8:29am

explained very well, thanks.