Inheritance in Java is a mechanism in which one object acquires all the properties and behaviors of a parent object. It is an important part of OOPs (Object Oriented programming system).

The idea behind inheritance in Java is that you can create new classes that are built upon existing classes. When you inherit from an existing class, you can reuse methods and fields of the parent class. Moreover, you can add new methods and fields in your current class also.

Inheritance represents the IS-A relationship which is also known as a parent-child relationship.

Reference id:

https://www.javatpoint.com/inheritance-in-java

Why inheritance is used in java:

for method overriding.

for code reuseble.

The most important use of inheritance in Java is code reusability. The code that is present in the parent class can be directly used by the child class.The key to understanding Inheritance is that it provides code re-usability. In place of writing the same code, again and again, we can simply inherit the properties of one class into the other.

When inheritance is used:

• Both classes are in the same logical domain.
• The subclass is a proper subtype of the superclass.
• The superclass’s implementation is necessary or appropriate for the subclass.
• The enhancements made by the subclass are primarily additive.

Reference id

https://www.google.com/search?client=firefox-b-lm&q=when+inheritance+is+usedv

https://www.google.com/search?client=firefox-b-lm&q=why+inheritance+in+java