## XLanguageSystem.java
import java.util.HashMap;
import java.util.LinkedList;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class XLanguageSystem {
  private String defaultLanguage = "en";
  private String tablePrefix = "lang_";
  private int cacheSize = 2;

  private Connection connection = null;
  private Statement statement = null;
  private ResultSet result = null;
  private HashMap<String, HashMap<String, String>> cache = new HashMap<String, HashMap<String, String>>();

  public XLanguageSystem() {
    System.out.println("Starting...");

    // --- database specific variables - begin ---
    String host = "localhost";
    String username = "xcache";
    String password = "C3sbMsKp5zFXKRyy";
    String database = "xcache";
    // --- database specific variables - end ---

    // --- connect to database - start ---
    try {
      System.out.print("Connection to database... ");
      Class.forName("com.mysql.jdbc.Driver").newInstance();

      this.connection = DriverManager.getConnection("jdbc:mysql://" + host + "/" + database, username, password);
      System.out.println("DONE");

      System.out.print("Creating Statement... ");
      this.statement = connection.createStatement();
      System.out.println("DONE\n");
    }
    catch(Exception e) {
      this.failure(e);
    }
    // --- connect to database - end ---

    // --- getting languages - begin ---
    this.selectQuery("SHOW TABLES LIKE '" + this.tablePrefix + "%'");

    try {
      while(this.result.next())
        this.createCache(this.result.getString(1).replace(this.tablePrefix, ""));
    }
    catch(Exception e) {
      this.failure(e);
    }

    this.freeResultSet();
    // --- getting languages - end ---
  }

  public void close() {
    System.out.println("\nShutting down...");

    this.freeResultSet();

    try {
      if(this.statement != null) {
        System.out.print("Closing Statement... ");
        this.statement.close();
        System.out.println("DONE");
      }

      if(this.connection != null) {
        System.out.print("Closing Connection... ");
        this.connection.close();
        System.out.println("DONE");
      }

      System.exit(0);
    }
    catch(Exception e) {
      this.failure(e);
    }
  }


  public String getEntry(String lang, String trans_id) {
    if(this.languageExists(lang)) { // language exists...
      if(this.cacheElementExists(lang, trans_id)) // element exists in language-cache...
        return this.getCacheElement(lang, trans_id); // return element from the language-cache
      else { // element does not exist in language-cache...
        String trans = this.selectTranslationFromDB(lang, trans_id); // select trans_id value from lang-table

        if(trans == trans_id) // trans-id value was not found in lang-table...
          trans = this.getDefaultTranslation(trans_id); // get default-translation for trans_id

        return trans;
      }
    }
    else // language does not exist...
      return this.getDefaultTranslation(trans_id);
  }

  public void addLanguage(String lang) {
    if(!this.languageExists(lang)) { // if language to add does not exists allready...
      System.out.print("Adding language '" + lang + "'... ");

      this.createCache(lang);

      String sqlQuery = "CREATE TABLE " + this.tablePrefix + lang + " ("
        + "id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,"
        + "trans_id VARCHAR(200) NOT NULL,"
        + "trans LONGTEXT NOT NULL,"
        + "userid INT(11) NOT NULL,"
        + "active TINYINT(1) DEFAULT '0',"
        + "KEY trans_id (trans_id),"
        + "KEY userid (userid)"
        + ") ENGINE=MyISAM;";

      this.updateQuery(sqlQuery);

      System.out.println("DONE");
    }
    else
      System.out.println("Language '" + lang + "' does allready exist.");
  }

  public LinkedList<String> getAvailableLanguages() {
    return new LinkedList<String>(this.cache.keySet());
  }

  public void removeCacheElement(String lang, String trans_id) {
    // if langueage exists and key exists in this language-cache... remove it...
    if(this.languageExists(lang) && this.cacheElementExists(lang, trans_id))
      this.cache.get(lang).remove(trans_id);
  }


  private void failure(Exception e) {
    System.out.println("FAILED\n");

    e.printStackTrace();

    System.exit(-1);
  }

  private void updateQuery(String sqlQuery) {
    try {
      this.statement.executeUpdate(sqlQuery);
    }
    catch(Exception e) {
      this.failure(e);
    }
  }

  private void selectQuery(String sqlQuery) {
    try {
      this.result = this.statement.executeQuery(sqlQuery);
    }
    catch(Exception e) {
      this.failure(e);
    }
  }

  private void freeResultSet() {
    try {
      if(this.result != null)
        this.result.close();
    }
    catch(Exception e) {
      this.failure(e);
    }
  }

  private void createCache(String lang) {
    this.cache.put(lang, new HashMap<String, String>());
  }

  private String getCacheElement(String lang, String trans_id) {
    System.out.println("Fetching '" + trans_id + "' for language '" + lang + "' from cache...");

    // get element and remove it temporarly from the cache...
    String trans = this.cache.get(lang).remove(trans_id);

    this.cache.get(lang).put(trans_id, trans); // add element back to the cache {element needs to be removed and readded to implement LFU}

    return trans;
  }

  private String selectTranslationFromDB(String lang, String trans_id) {
    System.out.println("Fetching '" + trans_id + "' for language '" + lang + "' from database...");

    this.selectQuery("SELECT trans FROM " + this.tablePrefix + lang + " WHERE trans_id = '" + trans_id + "' AND active = '1'");

    String trans = "";

    try {
      if(this.result.next()) { // found entry in lang-table...
        trans = this.result.getString(1); // get entry

        if(this.cache.get(lang).size() == this.cacheSize) { // cache is full...
          // remove first key entry {is the oldes in terms of LFU-policy}...
          for(String key : this.cache.get(lang).keySet()) {
            this.cache.get(lang).remove(key);
            break;
          }
        }

        this.cache.get(lang).put(trans_id, trans); // add found trans to cache...
      }
      else // entry not found in database...
        trans = trans_id; // set trans_id to be returned...
    }
    catch(Exception e) {
      this.failure(e);
    }

    this.freeResultSet();

    return trans;
  }

  private String getDefaultTranslation(String trans_id) {
    if(this.cacheElementExists(this.defaultLanguage, trans_id)) // trans_id exists in lang-cache of default language...
        return this.getCacheElement(this.defaultLanguage, trans_id); // return trans-id value from cache
    else // trans_id does not exist in lang-cache of default language...
      return this.selectTranslationFromDB(this.defaultLanguage, trans_id); // select trans-id value from lang-table...
  }

  private boolean languageExists(String lang) {
    return this.cache.containsKey(lang);
  }

  private boolean cacheElementExists(String lang, String trans_id) {
    return this.cache.get(lang).containsKey(trans_id);
  }


  public void printCache(String lang) {
    System.out.println("\n==========");

    for(String trans_id : this.cache.get(lang).keySet())
      System.out.println(trans_id + " => " + this.cache.get(lang).get(trans_id));

    System.out.println("==========\n");
  }

}

## Xtest.java
public class Xtest {
  public static void main(String[] args) {
    XLanguageSystem xcache = new XLanguageSystem();

    System.out.println("Available languages:");

    for(String lang : xcache.getAvailableLanguages())
      System.out.println(lang);

    System.out.println();

    xcache.addLanguage("de");
    xcache.addLanguage("fr");

    xcache.printCache("de");

    System.out.println(xcache.getEntry("de", "foo"));

    xcache.printCache("de");

    System.out.println(xcache.getEntry("de", "bar"));

    xcache.printCache("de");

    System.out.println(xcache.getEntry("de", "tar"));

    xcache.printCache("de");

    System.out.println(xcache.getEntry("de", "bar"));

    xcache.printCache("de");

    System.out.println(xcache.getEntry("de", "foo"));

    xcache.printCache("de");

    System.out.println("Removing trans_id 'foo' from cache of language 'de'...");

    xcache.removeCacheElement("de", "foo");

    xcache.printCache("de");

    xcache.close();
  }
}

## Xtest_output
Starting...
Connection to database... DONE
Creating Statement... DONE

Available languages:
de
fr
en

Language 'de' does allready exist.
Language 'fr' does allready exist.

==========
==========

Fetching 'foo' for language 'de' from database...
foo ist foobar

==========
foo => foo ist foobar
==========

Fetching 'bar' for language 'de' from database...
bar is barfoo

==========
foo => foo ist foobar
bar => bar is barfoo
==========

Fetching 'tar' for language 'de' from database...
tar ungleich zip

==========
tar => tar ungleich zip
bar => bar is barfoo
==========

Fetching 'bar' for language 'de' from cache...
bar is barfoo

==========
tar => tar ungleich zip
bar => bar is barfoo
==========

Fetching 'foo' for language 'de' from database...
foo ist foobar

==========
foo => foo ist foobar
bar => bar is barfoo
==========

Removing trans_id 'foo' from cache of language 'de'...

==========
bar => bar is barfoo
==========


Shutting down...
Closing Statement... DONE
Closing Connection... DONE