Inheritance

tags: OOPS

Explain the concept of Inheritance

• By using Inheritance, we can put the common behavior and characteristics in a base class which also known as super class. And then all the objects with common behavior inherit from this base class.
• It is also represented by IS-A relationship.
• Inheritance promotes code reuse, method overriding and polymorphism.

Which class in Java is superclass of every other class?

Object class.

What is the purpose of ‘this’ keyword in java?

• ‘this’ keyword refers to current instance of the object.
• useful for differentiating between instance variables and local variables.
• It can be used to call constructors.

Why Java does not support multiple inheritance?

• Multiple Inheritance means that a class can inherit behavior from two or more parent classes.
• If both the parent classes may have the same method, it leads to ambiguity.
• This is the main reason for Java not supporting Multiple Inheritance in implementation.
• But you can implement multiple interfaces in Java.

In OOPS, what is meant by composition?

• Composition is also known as strong “has-a” relationship.
• E.g. Class Car has a steering wheel.
• If a class holds the instance of another class, then it is called composition.
• In composition, the contained object is an integral part of the container object and cannot exist independently.

What is meant by aggregation?

• Aggregation is also known as weak “has-a” relationship.
• A student can be related to Library. A student can still exist without a library.
• Aggregation is a type of association relation in which objects can exists irrespective of each other.

Feature	Aggregation	Composition
Relationship	Weak “has-a”	Strong “has-a” (part-of)
Independence	Contained object can exist independently.	Contained object cannot exist independently.
Lifecycle	Independent lifecycles.	Dependent lifecycles.
Ownership	No strong ownership implied.	Strong ownership implied.

What is the purpose of ‘super’ keyword in java?

• It refers to parent class of an object.
• By using ‘super’ we can call a method of parent class from the method of a child class.
• We can also call the constructor of a parent class from the constructor of a child class by using ‘super’ keyword

Is it possible to use this() and super() both in same constructor?

No, As per Java specification, super() or this() must be the first statement in a constructor.

What are the types of inheritance in java

On the basis of class, there can be three types of inheritance in java: single, multilevel and hierarchical. In java programming, multiple and hybrid inheritance are supported through interface only.