Object from Subclass to Superclass

[Pan Niko]

Hello,

Im wondering if you can "convert" a subclass's object to superclass's.

[Wouter Oet]

You can't. Objects can't change type. You can however change the reference type to the object:

Child child = new Child();
Parent parent = child;

[Pan Niko]

And what happening if child has extra variables that Parent doesn't?

[Wouter Oet]

You'll lose scope to that variable/method. You can only access/invoke variables/methods that are defined in the parent. However if the Child class overrides one of these methods (not variables!) that method will be called instead of the method of the parent.

[Ivan Franko]

you lose extra variables...

[Pan Niko]

To make it clear

Parent newParent = new Parent("Paul");
Child newChild = new Child("Steven", 23, "English");

So if now do:

Parent newParent_2 = newChild;

newParent_2 will just hold name? "Steven"??

[Paul Clapham]

No. Variables don't contain anything except a reference to an object. And the object always contains the same data no matter what type of variables contain references to it.

However the compiler doesn't let you access anything except variables and methods which are declared for the type of variable. So in your example, the Child object continues to contain everything which a Child object normally contains, but the Parent variable which refers to it can only access variables and methods from Parent.

[Ivan Franko]

public class Parent {

	public String name;

	Parent(String name) {

		this.name = name;
	}

	public static void main(String args[]) {
		Parent newParent = new Parent("Paul");
		Child newChild = new Child("Steven", "English");

		Parent newParent_2 = newChild;
		

System.out.println(newParent_2.name); //you see on display "Steven"

	}
}

class Child extends Parent {

	public String country;

	Child(String name, String country) {
		super(name);
		this.country = country;
	}

}