Abstract classes and interfaces

Go back again static

Static method calls You can direct the method name ();

The call of non static methods should new An instance of an object . call

Static is executed only once

final

final Modification constant value cannot be modified for the second time

*final Prevent instruction reordering under multithreading , Ensure thread safety

final Decorated classes cannot be inherited

final The decorated method cannot be overridden

abstract class abstract

  Methods of abstract classes must be implemented by subclasses

You can't abstract classes new Can only be implemented by subclasses

Abstract methods must be in abstract classes

reflection Do abstract classes have constructors What is the meaning of being

There are constructors Used for subclass instantiation

Interface

All definitions of interfaces are abstract public abstract keyword interface

Interfaces must implement classes keyword implements yes Implementation interface

The interface supports multiple implementations

Interface cannot be instantiated There is no constructor in the interface

Can not be new But you can cooperate An anonymous class

Inner class

1. Member inner class

public class Outer {
private int id;
public void out(){
 External class methods 
}
class Intter{
public void in(){
 Inner class methods 
        }
    }
}

2. Static inner class

public class Outer {
private int id;
public void out(){
 External class methods 
}
public static class Intter{
public void in(){
 Inner class methods 
        }
    }
}

3. Local inner classes

public class Outer {
public void method(){
class Inner{
        }
    }
}

4. Anonymous inner class

public class Test {
public static void main(String[] args) {
new Apple().eat();
}
static class Apple{
public void eat(){
System.out.println(“1”);
        }
    }
}