Abstract classes and interfaces

１. Definition ： Use abstract Keyword decorated class , It's called an abstract class , Used in abstract classes abstract Keyword modification , Methods without method bodies are called abstract methods , Abstract methods must be defined in abstract classes . Interfaces are more abstract methods than abstract methods , use interface Methods of keyword modification , The interface is implemented with implements keyword .

２. difference

The abstract method of the interface can not write the modifier and abstract keyword .

A class can only inherit one abstract class , But multiple interfaces are allowed to be implemented , Its subclasses are called implementation classes .

Ordinary methods can be defined in abstract classes , Construction method , But ordinary methods and construction methods cannot be defined in the interface , from JDK 1.8 Start , There is a use default Methods of keyword modification , There are methods , Equivalent to ordinary methods of abstract classes , It's called the default method .

Members can be defined in abstract classes " Variable ", It can be modified when creating objects , The member variable defined in the interface is a constant , Assignment is required when defining , It is not allowed to be modified , Constants in abstract classes must use final Keyword modification .