interfaceDemo3.java

package Basics;

// https://www.youtube.com/watch?v=rM2f0mTie_Q&list=PLmOn9nNkQxJH0qBIrtV6otI0Ep4o2q67A&index=352
// https://www.youtube.com/watch?v=JQzwqQfzl08&list=PLmOn9nNkQxJH0qBIrtV6otI0Ep4o2q67A&index=353

// define a rule, standard, format
interface USB {
  // attr

  // method
  void start();

  void stop();
}

/**
 * Interface part 3
 *
 * <p>1) interface using : reflects OOP's Polymorphism 2) interface essentially defines the
 * "format", "standard" -> that can be implemented by the class
 *
 * <p>3) using cases : -> JDBC for DB
 *
 * <p>4) during development, we usually do "interface facing" development
 */
public class interfaceDemo3 {
  public static void main(String[] args) {
    // run
    Computer pc1 = new Computer();

    // wrong : 'USB' is abstract; cannot be instantiated
    // pc1.transferData(new USB());

    /** DEMO 1: interface's non anonymous class and non anonymous instance */
    // will use the Flash class, which implements USB interface
    Flash flash = new Flash();
    pc1.transferData(flash);

    System.out.println("============");

    /** DEMO 2: interface's non anonymous class and anonymous instance */
    pc1.transferData(new Printer());

    System.out.println("============");

    /** DEMO 3: interface's anonymous class and non anonymous instance */
    USB phone =
        new USB() {

          @Override
          public void start() {
            System.out.println("phone start");
          }

          @Override
          public void stop() {
            System.out.println("phone stop");
          }
        };

    pc1.transferData(phone);

    System.out.println("============");

    /** DEMO 4: interface's anonymous class and anonymous instance */
    pc1.transferData(
        new USB() {

          @Override
          public void start() {
            System.out.println("ipod start");
          }

          @Override
          public void stop() {
            System.out.println("ipod stop");
          }
        });
  }
}

class Computer {
  // attr

  // method
  // NOTE : this method gets any implementation which from USB interface
  //        and use its start, stop method, while start, stop method
  //        are NOT implemented in USB (USB is an interface), but
  //        in the implementation of USB (e.g. Flash, Printer)
  public void transferData(USB usb) {
    usb.start();
    // code that implements data transfer

    usb.stop();
    // code that implements stop
  }
}

class Flash implements USB {

  @Override
  public void start() {
    System.out.println("Flash start");
  }

  @Override
  public void stop() {
    System.out.println("Flash stop");
  }
}

class Printer implements USB {

  @Override
  public void start() {
    System.out.println("Printer start");
  }

  @Override
  public void stop() {
    System.out.println("Printer stop");
  }
}