java-design-patterns/marker/src/main/java/App.java

/**
 * The MIT License
 * Copyright © 2014-2019 Ilkka Seppälä
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Created by Alexis on 28-Apr-17.
 * With Marker interface idea is to make empty interface and extend it.
 * Basically it is just to identify the special objects from normal objects.
 * Like in case of serialization , objects that need to be serialized must implement serializable interface
 * (it is empty interface) and down the line writeObject() method must be checking
 * if it is a instance of serializable or not.
 * <p>
 * Marker interface vs annotation
 * Marker interfaces and marker annotations both have their uses,
 * neither of them is obsolete or always better then the other one.
 * If you want to define a type that does not have any new methods associated with it,
 * a marker interface is the way to go.
 * If you want to mark program elements other than classes and interfaces,
 * to allow for the possibility of adding more information to the marker in the future,
 * or to fit the marker into a framework that already makes heavy use of annotation types,
 * then a marker annotation is the correct choice
 */
public class App {

  /**
   * Program entry point
   *
   * @param args command line args
   */
  public static void main(String[] args) {

    final Logger logger = LoggerFactory.getLogger(App.class);
    Guard guard = new Guard();
    Thief thief = new Thief();

    if (guard instanceof Permission) {
      guard.enter();
    } else {
      logger.info("You have no permission to enter, please leave this area");
    }

    if (thief instanceof Permission) {
      thief.steal();
    } else {
      thief.doNothing();
    }
  }
}