One 、 What is an abstract class ？

abstract class ： stay java In language , use abstract class Keyword to define an abstract class , Define abstract side （ There is no method body ） Method must be in an abstract class , When subclasses inherit the abstract parent class, they must implement the abstract methods of the parent class （ Unless the subclass is also an abstract method ）; Abstract classes can define “ quote ”, But it cannot be instantiated , But it can point to objects of any subclass

Two 、 What is the interface ？

Interface ： use interface Keyword definition interface , Interfaces can define abstract methods （ Don't have to abstract modification ）, Ordinary methods and construction methods cannot be defined , But you can define default methods （default modification ）; An interface cannot define a member variable , Only constants can be defined ; Sure implement Multiple interfaces and allow “ multiple inheritance ”.

summary

adopt abstract The method of definition is abstract method , Only basic method definitions , There is no method body ;

When subclasses inherit the abstract parent class, they must implement the abstract methods of the parent class （ Unless the subclass is also an abstract method ）;

A class can only extends Inherit another class , But a class can implement Implement multiple interfaces ;

JDK 1.8 after , Allow definition of default Method （ The default method ）