Database.java

package simpledb;

import java.io.*;

/** Database is a class that initializes several static
 variables used by the database system (the catalog, the buffer pool,
 and the log files, in particular.)
 <p>
 Provides a set of methods that can be used to access these variables
 from anywhere.
*/

public class Database { // 2016 F
	private static Database _instance = new Database();
 private final Catalog _catalog;
 private BufferPool _bufferpool; 

 private final static String LOGFILENAME = "log";
 private LogFile _logfile;

 private Database() {
 	_catalog = new Catalog();
 	_bufferpool = new BufferPool(BufferPool.DEFAULT_PAGES);
 	try {
 _logfile = new LogFile(new File(LOGFILENAME));
 } catch(IOException e) {
 _logfile = null;
 e.printStackTrace();
 System.exit(1);
 }
 // startControllerThread();
 }

 /** Return the log file of the static Database instance*/
 public static LogFile getLogFile() {
 return _instance._logfile;
 }

 /** Return the buffer pool of the static Database instance*/
 public static BufferPool getBufferPool() {
 return _instance._bufferpool;
 }

 /** Return the catalog of the static Database instance*/
 public static Catalog getCatalog() {
 return _instance._catalog;
 }

 /** Method used for testing -- create a new instance of the
 buffer pool and return it
 */
 public static BufferPool resetBufferPool(int pages) {
 _instance._bufferpool = new BufferPool(pages);
 return _instance._bufferpool;
 }

 //reset the database, used for unit tests only.
 public static void reset() {
 	_instance = new Database();
 }

}