- Inheritance
- Types of Inheritance
- Why multiple inheritance is not possible in java in case of class?
Inheritance is a mechanism in which one object acquires all the properties and behaviours of parent object.
The idea behind inheritance is that you can create new classes that are built upon existing classes. When you inherit from an existing class, you reuse (or inherit) methods and fields, and you add new methods and fields to adapt your new class to new situations.
Inheritance represents the IS-A relationship.
Why use Inheritance?
- For Method Overriding (So Runtime Polymorphism).
- For Code Reusability.
Syntax of Inheritance
- class Subclass-name extends Superclass-name
- {
- //methods and fields
- }
| The keyword extends indicates that you are making a new class that derives from an existing class. In the terminology of Java, a class that is inherited is called a superclass. The new class is called a subclass. |
Understanding the simple example of inheritance
As displayed in the above figure, Programmer is the subclass and Employee is the superclass. Relationship between two classes is Programmer IS-A Employee.It means that Programmer is a type of Employee.
- class Employee{
- float salary=40000;
- }
- class Programmer extends Employee{
- int bonus=10000;
- public static void main(String args[]){
- Programmer p=new Programmer();
- System.out.println("Programmer salary is:"+p.salary);
- System.out.println("Bonus of Programmer is:"+p.bonus);
- }
- }
Output:Programmer salary is:40000.0
Bonus of programmer is:10000
In the above example,Programmer object can access the field of own class as well as of Employee class i.e. code reusability.
Types of Inheritance
On the basis of class, there can be three types of inheritance: single, multilevel and hierarchical.
Multiple and Hybrid is supported through interface only. We will learn about interfaces later.
Multiple inheritance is not supported in java in case of class.
When a class extends multiple classes i.e. known as multiple inheritance. For Example:
Que) Why multiple inheritance is not supported in java?
- To reduce the complexity and simplify the language, multiple inheritance is not supported in java. For example:
- class A{
- void msg(){System.out.println("Hello");}
- }
- class B{
- void msg(){System.out.println("Welcome");}
- }
- class C extends A,B{//suppose if it were
- Public Static void main(String args[]){
- C obj=new C();
- obj.msg();//Now which msg() method would be invoked?
- }
- }
Questions and Anwsers
Which class is the superclass for every class.
| Object class. |
Why multiple inheritance is not supported in java?
- To reduce the complexity and simplify the language, multiple inheritance is not supported in java in case of class
What is super in java?
| It is a keyword that refers to the immediate parent class object |
Can you use this() and super() both in a constructor?
|
What is composition?
| Holding the reference of the other class within some other class is known as composition. |
What is difference between aggregation and composition?
| Aggregation represents weak relationship whereas composition represents strong relationship. For example: bike has an indicator (aggregation) but bike has an engine (compostion). |
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