Overview of static inner classes and non static inner classes

distinguish Concept ：

According to whether there is static Modifiers are divided into static inner classes and non static inner classes ,
Yes static Decorated as static inner class ,
No, static Decorated as a non static inner class

Static inner class

Statically named inner classes

cross-categorical If you use it Must be “ External class class name . Internal class name ”
This category If you use it need not Use the external class name

example ：

Body class ：
package com.jd;
/**
 *  External class 
 */
public class Body {
	/**
	 *  Statically named inner classes 
	 */
	public static class Heart{
		public void beat(){
			System.out.println(" It's beating ...");
		}
	}
}
Test class ：
package com.jd;
import com.jd.Body.Heart;
public class Test {
	public static void main(String[] args) {
		Heart heart = new Body.Heart();
		heart.beat();
	}
}

Medium

Heart heart = new Body.Heart();
heart.beat();

Static inner classes can only direct Access to external classes Static member variables and methods ,
Can pass Create an object of an external class Use indirectly Non static member variables and methods .

public class OutClass {
	private double weight=72;	
	public static void print(String name) {
		System.out.println(name);
	}	
	static class InClass{
		{
			double weight = new OutClass().weight;
			// because weight It's not static , Therefore, when using in static inner classes, you must first create external class objects 
			print("Tom");
			// because print Method is a static method , So you can use it directly .
		}
	}
}

Internal classes defined in non external classes are the same as local variables , Its use range starts from the defined position to the end of its direct statement block .

public class OutClass {
	public static void main(String[] args) {
		if(args!=null) {
			class InClass{				
			}
		}
		InClass inClass = new InClass();
		// Can't create object , Because the scope of the inner class cannot work here 
	}
}

Static members are only allowed in well-known static inner classes （ Static attribute 、 Static code blocks and static methods ）.

Static anonymous inner class

Just add static that will do .

class Father {
	public void eat() {
		System.out.println(" Eat with chopsticks ....");
	}
}
/**
 *  External class 
 */
public class OutClass {
	/**
	 *  Anonymous inner class 
	 */
	static Father son = new Father(){	
		@Override
		public void eat() {
			System.out.println(" Eat with chopsticks ....");
		}
	};
}

notes ：

If static Inner classes can only be defined directly in outer classes . Not in the method , Block of code .

public class OutClass {
	public static void main(String[] args) {	
		/**
		 *  Statically named inner classes 
		 */
		static class InClass {
			public void printInfo() {
				System.out.println(" I'm a famous inner class ");
			}
		}
	}
}

Non static inner class

Non static inner classes defined directly in classes , Create objects in static methods , must “ Explicit ” Create an external class object