Abstract classes and interfaces

abstract class , Abstract method , Summary of the interface

Abstract method	abstract class	Interface
Abstract methods have no method bodies , Give it to the subclass implementation	Abstract classes do not necessarily have static methods , Those with static methods must be abstract classes .	JDK1.8 Before ： Only method declarations can be written in interfaces , Instead of writing the specific implementation of the method JDK1.8 after ： Interfaces can write specific implementations of method declarations .
Abstract method modifiers It can't be private,final,static（ Because subclass implementation is required ）.	Can't be instantiated , Can only be inherited .	There is no constructor in the interface , Can't be instantiated .
Abstract methods must be defined in abstract classes or interfaces .	Subclasses of abstract classes may not implement all abstract methods , But it must also be an abstract class .( Abstract derived classes )	Interfaces can only inherit interfaces , Can't inherit class , Interface supports multiple inheritance .
nothing	The constructor of an abstract class cannot be defined as private .（ The subclass constructor will call the parent constructor .）	The member variables defined in the interface are... By default public static final Modified static constants
nothing	Abstract class cannot be defined as final,final ( Modified classes cannot be inherited ).	Methods in interfaces : The default is public abstract An abstract method of embellishment . JDK1.8 There cannot be static methods before , There can be no ordinary way . JDK1.8 After that, there can be static methods , There can be a common way .
nothing	Abstract classes can implement interfaces , You can inherit concrete classes , You can also inherit abstract classes .	Internal classes defined in interface , The default is public static Decorated static inner class .
nothing	There are common methods in abstract classes , You can also have static methods .	nothing

Similarities and differences between abstract classes and interfaces ：

The same thing	Difference
① Abstract classes and interfaces cannot be instantiated	① Abstract classes have construction methods , Interface has no constructor
② Abstract classes and interfaces can define abstract methods , Subclass / The implementation class must override these abstract methods	② Abstract classes can contain ordinary methods , The interface can only be public abstract Modify abstract methods （Java8 After that you can ）
nothing	③ Abstract class can only inherit only , Interfaces can inherit more
nothing	④ Abstract classes can define various types of member variables , The interface can only be public static final Modified static constants
nothing	⑤ The access type of an abstract method in an abstract class can be public,protected and （ Default type , although eclipse Do not report wrong , But it should not ）, But an abstract method in an interface can only be public Type of , And the default is public abstract type .
nothing	⑥ Static methods can be included in abstract classes , Static methods cannot be included in an interface .

Thank an unknown blogger for his summary , In this blog, I learned a lot from each other's summary knowledge points ： Portal