Inheritance in java

What is Inheritance in java?

Inheritance is an important part of Object-Oriented Programming (OOP) languages.

Inheritance is a mechanism where one class acquires all the properties and behaviors (methods and fields) of another class is called Inheritance.

We use extends Keyword to inherit the properties of one class to another class.

Using the extends keyword, the child class will be able to inherit all the properties of the parent class but
except for the private properties of the parent class.

The syntax of Java Inheritance Example:

class Parent {
.....
.....
}

class Child extends Parent {
.....
.....
}

In the above example Parent class is called the superclass and the child class is called the subclass, where the child class extends the Parent class and gets all properties and behaviors of the parent class.

If any class extends to any other class using the keyword extends mean’s that class is child class.

Every class has a superclass except one class that is the Object class. Object class the only class in Java that doesn’t extend another class.

If you don’t declare a superclass of your class then your class implicitly extends the class Object as a superclass.

Why use inheritance in java?

For Method Overriding.
For Code Re-usability.

What is the benefit of using inheritance in java?

Using Method Overriding we can be achieved runtime polymorphism in java. Code Reusability, reusability is a mechanism which provides facilitates you to reuse the fields and methods of the existing class (Parent Class)
when you create a new class (Child class). You can use the same fields and methods already defined in the Parent class.

IS-A Relationship Example.

public class Animal {
}

public class Dog extends Animal {
}

public class Cat extends Animal {
}

In the above example Dog is the subclass and Animal is the superclass. The relationship between the two classes is Dog IS-A Animal and Cat IS-A Animal. It means that Dog is a type of Animal and also Cat is a type of Animal.

Java Inheritance program Example:

package com.testing;

//concept of inheritance 

//base class 
class Father  
{ 
 // the Father class has two fields 
 public int money; 
 public int gold; 
       
 // the Father class has one constructor 
 public Father(int money, int gold) 
 { 
     this.money = money; 
     this.gold = gold; 
 } 
       
 // the Father class has three methods 
 public void subtractMoney(int decrement) 
 { 
	 money -= decrement; 
 } 
       
 public void addMoney(int increment) 
 { 
	 money += increment; 
 } 
   
 // toString() method to print info of Father 
 public String toString()  
 { 
     return("Kg of gold are "+gold 
             +"\n"
             + "Money of Father is "+money); 
 }  
} 

//derived class 
class Son extends Father  
{ 
   
 // the Son subclass adds one more field 
 public int house; 

 // the Son subclass has one constructor 
 public Son(int gold,int money, 
                     int noOfHouse) 
 { 
     // invoking base-class(Father) constructor 
     super(gold, money); 
     house = noOfHouse; 
 }  
       
 // the Son subclass adds one more method 
 public void setHouse(int newValue) 
 { 
	 house = newValue; 
 }  
   
 // overriding toString() method 
 // of Father to print more info 
 @Override
 public String toString() 
 { 
     return (super.toString()+ 
             "\nNumber of house is "+house); 
 } 
   
} 

//driver class 
public class Test  
{ 
 public static void main(String args[])  
 { 
       
     Son son = new Son(100000,3, 2); 
     System.out.println(son.toString()); 
           
 } 
}

Output:

Kg of gold are 3
Money of Father is 100000
Number of house is 2

In the above program, when we created the object of Son class, a copy of the all methods and fields of the superclass (Father class) acquire memory in the object of son class. That is why by using the object of the child class we can also access the members of a parent class.

Types of Inheritance in Java

There are different types of inheritance.
Below are the different types of inheritance which are supported by Java.

Single Inheritance
Multilevel Inheritance
Hierarchical Inheritance
Multiple Inheritance
Hybrid Inheritance

What is Single Inheritance?

When subclasses inherit the features of one superclass is known as single inheritance.

In the above image, A class is a base class for the derived class B.

Single Inheritance Example:

package com.testing;
class Animal {
	void eat() {
		System.out.println("Animal are eating....");
	}
}

class Cat extends Animal {
	void meow() {
		System.out.println("Cat is meow");
	}
}

class Test{
	public static void main(String args[]) {
		Cat cat = new Cat();
		cat.meow();
		cat.eat();
	}
}

OutPut:

Cat is meow.... Animal are eating....

In the above example, the Cat class inherits the features of the Animal class.

What is Multilevel Inheritance?

When one class inherits multiple class features, is known as a multilevel inheritance in java.

In Java, any driving class can not directly access the grandparent’s members. like C class can not directly inherit the features of A-class. C class inherits the features of A-class through B class.

In the above image, C class inherits the features of B class, and it also inherits the features of A-class through B class.

Multilevel Inheritance Example:

package com.testing;
class Animal {
	void eat() {
		System.out.println("Animal are eating....");
	}
}

class Cat extends Animal {
	void meow() {
		System.out.println("Cat is meow");
	}
}

class Test{
	public static void main(String args[]) {
		Cat cat = new Cat();
		cat.meow();
		cat.eat();
	}
}

OutPut:

Cat is meow....
Animal are eating....

In the above example, the Cat class inherits the features of the Animal class.

What is Multilevel Inheritance?

When one class inherits multiple class features, is known as a multilevel inheritance in java. In Java, any driving class can not directly access the grandparent’s members. like C class can not directly inherit the features of A-class. C class inherits the features of A-class through B class.

In the above image, C class inherits the features of B class, and it also inherits the features of A-class through B class.

Multilevel Inheritance Example:

package com.testing;

class Animal {
	void eat() {
		System.out.println("Animal are eating....");
	}
}

class Cat extends Animal {
	void meow() {
		System.out.println("Cat is meow....");
	}
}

class Kitten extends Cat {
	void weep() {
		System.out.println("Kitten is weeping....");
	}
}

class Test {
	public static void main(String args[]) {
		Kitten k = new Kitten();
		k.weep();
		k.meow();
		k.eat();
	}
}

OutPut:

Kitten is weeping....
Cat is meow....
Animal are eating....

In the example given above, the Kitten class inherits the Cat class which again inherits the Animal class, so there is a multilevel inheritance.
As you can see in the example Kitten class can not directly inherit the features of the Animal class, It can inherit the features of the Animal class through the Cat class.

What is Hierarchical Inheritance in java?

When a single class is inherited by multiple classes, it is known as hierarchical inheritance

In the above image, A class is inherited by class B and C.

Hierarchical Inheritance Example:

package com.testing;
class Animal {
	void eat() {
		System.out.println("Animal are eating....");
	}
}

class Cat extends Animal {
	void meow() {
		System.out.println("Cat is meow....");
	}
}

class Dog extends Animal {
	void bark() {
		System.out.println("Dog is barking....");
	}
}

class Test {
	public static void main(String args[]) {
		Cat c = new Cat();
		c.meow();
		c.eat();
		Dog d = new Dog();
		d.bark();
		d.eat();
	}
}

Output:

Cat is meow....
Animal are eating....
Dog is barking....
Animal are eating....

In the example given above, the Cat class inherits the Animal class, and the Dog class also inherits the Animal class so there is a Hierarchical inheritance.

What is Multiple Inheritance?

When one subClass has multiple superclass and inherits features from all parent classes, is known as Multiple inheritances in java.

In Java, multiple Inheritance is not supported by Java Class, but we can achieve multiple Inheritance through Interfaces in Java.

In the above image, C class is inherited by class A and B

What is Hybrid Inheritance?

Hybrid Inheritance is a mix of two or more different types of inheritance.

We already know Java does not support multiple inheritances through classes, so Hybrid Inheritance is also not supported by multiple inheritances through classes. It can also achieve through Interfaces in Java.

Why Multiple Inheritance is not supported by Java Class?

Multiple Inheritance is not supported by the Java class because of the ambiguity problem.

Let’s try to understand through example, suppose A, B, and C are three classes. C class inherits A and B classes.
Now if A and B classes have the same method with all functionality and you call it from C class(child class) object, there will be ambiguity to call the method of A or B class. The C class object not able to identify to which class object need to call because in both class method is same.

Multiple Inheritance Example:

package com.testing;

class A {
	void msg() {
	System.out.println("How are you?");
	}
}

class B {
	void msg() {
	System.out.println("You are from?");
	}
}

class C extends A,B{ 
     public static void main(String args[]) {
      C obj = new C();
      obj.msg();
    }
}

Output:

Compile Time Error

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Hope this was helpful for you. If you have any questions please feel free to leave a comment. Thank you for reading.

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