Special Java class usage: File class, internal class, local class, Anonymous class

1. File class

Test is a file class.

class Test {   static void method() {      //...   }}public class Driver {   public static void main(String[] args) {      Test.method();   }}

2. Internal class

class OuterClass {   int outerData;   static int s_outerData;   void outerMethod() {}   static void s_outerMethod() {}   class InnerClass {      int innerData;      void innerMethod() {         innerData = outerData;         innerData = s_outerData;         outerMethod();         s_outerMethod();      }   }}

3. Local class

A local class is a class defined inside a method.

class A {   int data;   void method() {      class B {         int local_data;         void local_method() {            System.out.println("I'm the method in the local class.");         }      }   }}

4. Anonymous class

An anonymous class is also called an anonymous internal class. It is actually an unknown local class.

class Test {   void method(new Object() {      public String toString() {         System.out.println("Hi, I'm an anonymous class.");      }   });}