Answered: Add missing code to turn this class a…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Add missing code to turn this class a singleton in Java

package com.gamingroom;

import java.util.ArrayList;
import java.util.List;

/**
* A singleton service for the game engine */
public class GameService {

/**
* A list of the active games
*/
private static List<Game> games = new ArrayList<Game>();

/*
* Holds the next game identifier
*/
private static long nextGameId = 1;

// FIXME: Add missing pieces to turn this class a singleton

/**
* Construct a new game instance
*
* @param name the unique name of the game
* @return the game instance (new or existing)
*/
public Game addGame(String name) {

// a local game instance
Game game = null;

// FIXME: Use iterator to look for existing game with same name
// if found, simply return the existing instance

  // if not found, make a new game instance and add to list of games
  if (game == null) {
   game = new Game(nextGameId++, name);
   games.add(game);
  }

// return the new/existing game instance to the caller
return game;
}

/**
* Returns the game instance at the specified index.
* <p>
* Scope is package/local for testing purposes.
* </p>
* @param index index position in the list to return
* @return requested game instance
*/
Game getGame(int index) {
return games.get(index);
}

/**
* Returns the game instance with the specified id.
*
* @param id unique identifier of game to search for
* @return requested game instance
*/
public Game getGame(long id) {

// a local game instance
Game game = null;

// FIXME: Use iterator to look for existing game with same id
// if found, simply assign that instance to the local variable

return game;
}

/**
* Returns the game instance with the specified name.
*
* @param name unique name of game to search for
* @return requested game instance
*/
public Game getGame(String name) {

// a local game instance
Game game = null;

// FIXME: Use iterator to look for existing game with same name
// if found, simply assign that instance to the local variable

return game;
}

/**
* Returns the number of games currently active
*
* @return the number of games currently active
*/
public int getGameCount() {
return games.size();
}
}

Game.java

package com.gamingroom;

/**
* A simple class to hold information about a game
*
* <p>
* Notice the overloaded constructor that requires
* an id and name to be passed when creating.
* Also note that no mutators (setters) defined so
* these values cannot be changed once a game is
* created.
* </p>
*
*
*
*/
public class Game {
long id;
String name;

/**
* Hide the default constructor to prevent creating empty instances.
*/
private Game() {
}

/**
* Constructor with an identifier and name
*/
public Game(long id, String name) {
  this();
  this.id = id;
  this.name = name;
}

/**
* @return the id
*/
public long getId() {
return id;
}

/**
* @return the name
*/
public String getName() {
return name;
}

@Override
public String toString() {

return "Game [id=" + id + ", name=" + name + "]";
}

}

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