CODEWITHSUNDEEP
java
Jay
Jay

Reputation: 185

Difference between "instantiated" and "subclass"

I was reading a Java tutorial and it said:

Abstract classes cannot be instantiated, but they can be subclassed.

what does this mean? I thought one had to instantiate in order to create a subclass? This line has really confused me, any and all help is much appreciated.

Upvotes: 2

Views: 1021

Answers (3)

Yash Pancholi
Yash Pancholi

Reputation: 11

A subclass can get all the properties/methods that its parent class has, whereas, instantiated class is when you make an instance of that parent class in memory.

Upvotes: 1

Raunak Agarwal
Raunak Agarwal

Reputation: 7228

When you say instantiated it means you would like to create the object of the class. Sub-class is the inheriting child. For example,

abstract class A{
  //Class A is abstract hence, can not be instantiated. The reason being abstract class provides the layout of how the concrete sub-class should behave. 

   pubic abstract void doSomething();
   //This abstract method doSomething is required to be implemented via all the sub-classes. The sub-class B and C implement this method as required.

}

class B extends A{
   //Class B is subclass of A
  public void doSomething(){ System.out.println("I am class B"); }
}
class C extends A{
   //Class C is subclass of A
  public void doSomething(){ System.out.println("I am class C"); }
}

if you try to do this, it would generate an exception

A a = new A();

But this would work fine.
B b = new B();
or 
A a = new B(); //Note you are not instantiating A, here class A variable is referencing the instance of class B

Upvotes: 0

tckmn
tckmn

Reputation: 59283

Instantiate:

AbstractClass a = new AbstractClass(); //illegal

Subclass:

class ConcreteClass extends AbstractClass { ... }
ConcreteClass c = new ConcreteClass(); //legal

You must create a new class that extends the abstract class, implement all of the abstract methods, and then use that new class.

Note that you can also do this:

class ConcreteClass extends AbstractClass { ... }
AbstractClass a = new ConcreteClass(); //legal

Upvotes: 4

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