CODEWITHSUNDEEP
java
shraddha
shraddha

Reputation: 883

related to abstract class reference holding object of its derived class

class A is abstract and class B extends class A now class A reference can hold object of class B,that is

A aObj = new B();

and assume class B has some extra methods.... like

class A
{
public show();
}
class B extends A
{
public show(){}
public method1(){}
private method2(){}
}

now tell me what things variable aObj can access from class B can it access everything?

Upvotes: 1

Views: 1165

Answers (3)

extraneon
extraneon

Reputation: 23950

aObj can only use show() as the compiler thinks aObj is of type A, and the only known method of A is show().

If you know that you actually have a B you can cast that object to a B:

if (aObj instanceof B.class) {
  B bObj = (B) aObj;
  bObj.method1(); //OK
} else {
  log.debug("This is an A, but not a B");
}
aObj.show();

Upvotes: 2

Colin Gislason
Colin Gislason

Reputation: 5589

For reference and completeness, here's a list of the possibilities:

A aObj = new B();
aObj.show(); // Works
aObj.method1(); // Error
aObj.method2(); // Error

And with casting to B: 

B bObj = (B)aObj; bObj
bObj.show(); // Works
bObj.method1(); // Works
bObj.method2(); // Works inside bObj, but error otherwise

Upvotes: 3

Marcelo Cantos
Marcelo Cantos

Reputation: 185842

aObj only sees the public show() method. If you cast aObj to B, you can then access public method1(). public method2() is only accessible to the implementation of B.

Upvotes: 3

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