Inheritance
The inheritance is oop concept in which the class inherit state and behavior to any other class.
inheritance can be achieve by using a super class and a subclass.
A super class is type of class which provide state and behavior to subclass.
A subclass is type of class which the subclass consume state and behavior provided by super class.
The programmer can achieve inheritance by using key word called as extend
every java object by default inherit from a super most class called as object class.
The syntax of Java Inheritance
class Subclass-name extends Superclass-name
{
//methods and fields
}
The extends keyword indicates that you are making a new class that derives from an existing class. The meaning of “extends” is to increase the functionality.
In the terminology of Java, a class which is inherited is called a parent or superclass, and the new class is called child or subclass.
Java Inheritance Example
As displayed in the above figure, Programmer is the subclass and Employee is the superclass. The relationship between the 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:10000In 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 in java
On the basis of class, there can be four types of inheritance in java:
1. single inheritance
2. multilevel inheritance
3. multiple inheritance
4. hierarchical inheritance
In java programming, multiple and hybrid inheritance is supported through interface only. We will learn about interfaces later.
Note: Multiple inheritance is not supported in Java through class.
When one class inherits multiple classes, it is known as multiple inheritance. For Example:
Single Inheritance Example
When a class inherits another class, it is known as a single inheritance. In the example given below, Dog class inherits the Animal class, so there is the single inheritance.
File: TestInheritance.java
class Animal{
void eat(){System.out.println(“eating…”);}
}
class Dog extends Animal{
void bark(){System.out.println(“barking…”);}
}
class TestInheritance{
public static void main(String args[]){
Dog d=new Dog();
d.bark();
d.eat();
}}
Output:
barking...
eating...Multilevel Inheritance Example
When there is a chain of inheritance, it is known as multilevel inheritance. As you can see in the example given below, BabyDog class inherits the Dog class which again inherits the Animal class, so there is a multilevel inheritance.
File: TestInheritance2.java
class Animal{
void eat(){System.out.println(“eating…”);}
}
class Dog extends Animal{
void bark(){System.out.println(“barking…”);}
}
class BabyDog extends Dog{
void weep(){System.out.println(“weeping…”);}
}
class TestInheritance2{
public static void main(String args[]){
BabyDog d=new BabyDog();
d.weep();
d.bark();
d.eat();
}}
Output:
weeping...
barking...
eating...Hierarchical Inheritance Example
When two or more classes inherits a single class, it is known as hierarchical inheritance. In the example given below, Dog and Cat classes inherits the Animal class, so there is hierarchical inheritance.
File: TestInheritance3.java
class Animal{
void eat(){System.out.println(“eating…”);}
}
class Dog extends Animal{
void bark(){System.out.println(“barking…”);}
}
class Cat extends Animal{
void meow(){System.out.println(“meowing…”);}
}
class TestInheritance3{
public static void main(String args[]){
Cat c=new Cat();
c.meow();
c.eat();
//c.bark();//C.T.Error
}}
Output:
meowing...
eating...Q) Why multiple inheritance is not supported in java?
To reduce the complexity and simplify the language, multiple inheritance is not supported in java.
Consider a scenario where A, B, and C are three classes. The C class inherits A and B classes. If A and B classes have the same method and you call it from child class object, there will be ambiguity to call the method of A or B class.
Since compile-time errors are better than runtime errors, Java renders compile-time error if you inherit 2 classes. So whether you have same method or different, there will be compile time error.
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?
}
}
output:
Compile Time Error