What is class , abstract class & interface .

Source: Dev.to

What is class ?

• A class is a blueprint from which we create objects.
• We declare a class with the class keyword.
• Inside the class we can directly write fields (non‑static / static), blocks (non‑static / static), constructors, concrete methods (non‑static / static), inner classes, interfaces, and so on.
• Generally, we create an object of a class with the new keyword.
• A class is also a user‑defined data type.
• We cannot write abstract methods inside a normal class.

Abstract Class

• An abstract class is declared with the abstract keyword.
• We cannot create an object of an abstract class.
• An abstract class may contain:
  • Non‑abstract (concrete) methods
  • Abstract methods
  • Non‑static fields
  • Static fields
• An abstract class cannot be final.

Note

• An abstract method has no body; its implementation must be provided in a subclass.

Interface

• An interface is a blueprint that contains abstract methods and constant (public static final) variables.
• We declare an interface with the interface keyword.
• Using interfaces we can achieve multiple inheritance.