Inheritance in Java

Inheritance

                    Inheritance is the process of reusing the code used in similar class, or a class that is derived from another class is called a subclass (also a derived class, extended class, or child class). The class from which the subclass is derived is called a superclass (also a base class or a parent class).

                    Every class has one and only one direct superclass (single inheritance). In the absence of any other explicit superclass, every class is implicitly a subclass of Object.

Example:

class User
{
	String name;
	int age;
	long ph;
	void salary()
	{
		System.out.println("salary");
	}
}

class Employee extends User
{
	String specialization;
}

class Manager extends User
{
	String department;
}

class Main
{
	public static void main(String[] args) {
		Employee e1=new Employee();
			e1.name="Candid";
			e1.age=22;
			e1.ph=123456789l;
			e1.specialization="Java";
		Manager m1=new Manager();
			m1.name="java";
			m1.age=25;
			m1.ph=345789l;
			m1.department="HR";
			
			System.out.println(e1.name);
			System.out.println(e1.age);
			System.out.println(e1.ph);
			System.out.println(e1.specialization);
			
			System.out.println(m1.name);
			System.out.println(m1.age);
			System.out.println(m1.ph);
			System.out.println(m1.department);
			
	}}

Inheritance not supported by Java

Multiple inheritance(a class cannot has more than one super class) is not supported in java

Example of multiple inheritance(not supported in java)

class Vehicle
{

}

class Car
{

}
class Truck extends Vehicle, Car
{

}

In the above example class Truck tries to occur the property of both Vehicle and Car Which makes the code to fail at compilation in java.

If we need the both the property of Vehicle and Car in Truck class we can redesign the code as

class Vehicle
{

}

class Car extends Vehicle
{
	// occurs the property of class Vehicle
}

class Truck extends Car
{
	// occurs the property of both car and vehicle
}

Default super class in Java

Every class in java by defaults extends the class Object from java.lang package

Example:

class A
{
 
}
 
class B extends A
{
 
}

Inheritance with constructor and super()

Constructor cannot be inherited, Only the member of the class and methods can be inherited.

But, subclass constructor can access the super class constructor by using super() in its first line.

class A 
{
	A()
	{

	}
}

class B extends A 
{
	B()
	{
		super();

	}
}

Inheritance with static variables

There is no need for inheriting static variable, static variable are shared values they can be accessed in any class by specifying its class name. A subclass inherits all of the public and protected members of its parent, no matter what package the subclass is in. In the below example

Example

class A {
	static int a = 10;
}

class B extends A {

}

public class StaticVariableInheritance
{
	public static void main(String[] args) {
		System.out.println(B.a);
		System.out.println(A.a);
	}
}

The above code compiles fine and produces the output

10

10

 Inheritance with static methods

Same as variable there is no need for inheriting the static method, simply static method cannot be inherited.

Inheritance with private variables & methods

Since private variable and methods are accessed only within the class, they cannot be inherited

Inheritance with abstract class & methods

When a class extends the abstract class all its abstract methods must be implemented in the subclass unless the subclass is also abstract. Abstract class are made to be inherited.

Inheritance with final variable and methods

Final variable and method can be inherited but final method cannot be changed or overridden in its subclass.

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