Internal class learning notes

Class is nested in a class , It's called an inner class

Member inner class

The member of a class is a class , The inner class of a member can access all the properties and methods of the outer class , Even if it is private、static Of
Members in inner class are private when , Can only be accessed inside an external class ; The members are public when , You can visit anywhere
Member inner class cannot have static Method ; There can be static Domain , Must be final Of
Depends on external classes , So you have to create an external class to access the internal class

public class Test {
    
    public static void main(String[] args) {
    
        Car car = new Car();
        car.run();
		
		//  Create inner class objects . Access internal class members , You must first have an object of an external class 
        Car.Bike bike1 = car.new Bike();
        bike1.run();	// days = 15

        Car.Bike bike = new Car().new Bike();
        bike.run();	// days = 5;
    }
}

class Car {
     //  External class 
    class Bike {
     //  Inner class 
        public int value;
        public void run() {
    
            days += 5;
            System.out.println("bike run " + days);
        }
    }

    private int days;

    public void run() {
    
        days = 10;
        System.out.println("car run " + days);
    }
}

Local inner classes

Nested in method 、 Internal classes in the scope , Access is only in its method or scope . A local inner class is actually a local variable of a method , So it can't be used public、private、protected、static modification

Anonymous inner class

A class without a name , Can only be used once . Anonymous inner classes must be inherited parent classes or implement interfaces
There are several methods in the interface , You have to rewrite a few methods ; How many abstract methods does an abstract class have , You have to rewrite these abstract methods
Appearing in ordinary use Most frequent Of
Anonymous inner classes cannot have access modifiers 、static, Static members cannot be defined 、 Method 、 class

abstract class Per{
    
	public abstract void eat();
	public abstract void run();
}

public class tt {
    
    public static void main(String[] args) {
    
        Per per = new Per() {
    
            @Override
            public void eat() {
     }

            @Override
            public void run() {
     }
        };
    }
}	   

such as Android When listening for events in , Anonymous inner classes are used .

Static inner class

static Decorated inner class —— Static inner class
Static inner classes do not depend on the creation of outer classes , You cannot use non static members of an external class
Static inner classes can create instances directly , Instead of using external classes

   //  Create a static inner class instance directly 
   new OuterClass.InnerClass().run();

public class Test {
    
    public static void main(String[] args) {
    
        OuterClass.InnerClass innerClass = new OuterClass.InnerClass();
        innerClass.run();
    }
}

class OuterClass {
    
    static class InnerClass {
    
        public void run() {
    
            System.out.println("static InnerClass run");
        }
    }
}