stopwatch.java

J2ME平台上经典的stoSwatch系统。系统架构清晰

package stopwatch;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.rms.*;

public class StopWatch extends MIDlet {

  // preferences database name
  private static final String PREFERENCES_DATABASE = "Preferences";

  static StopWatch instance;
  MainMenu mainMenu = new MainMenu();
  public StopWatch() {
    instance = this;
  }

  public void startApp() {
    // Load any previously-saved user options.
    loadOptions();
    // Display the main stop watch screen.
    Display.getDisplay(this).setCurrent(mainMenu);
  }


  public void pauseApp() {
  }

  public void destroyApp(boolean unconditional) {
    // Save all options.
    saveOptions();

    // Release references.
    mainMenu.destroy();
    mainMenu = null;
  }


  public static void quitApp() {
    instance.destroyApp(true);
    instance.notifyDestroyed();
    instance = null;
  }

  /**
   * <p>Retrieves the user preferences stored off in the local
   * database file.</p>
   */
  private void loadOptions() {
    RecordStore database = null;
    try {
      // open the database of stored stock symbols
      database = RecordStore.openRecordStore(PREFERENCES_DATABASE, true);

      // we store the display format option value as the only record in the
      // database.
      String            displayFormatString = null;
      RecordEnumeration enum = database.enumerateRecords(null, null, false);

      // This loop will just extract the first element (our display format
      // option) and then quit the loop.
      while (enum.hasNextElement()) {
        displayFormatString = new String(enum.nextRecord());
        break;
      }

      // set the display format
      if (displayFormatString != null) {
        // Convert the stored string into an integer that represents the
        // display time format.
        int displayFormat = Integer.parseInt(displayFormatString);
        // Now, set it as the currently selected display time format.
        mainMenu.setDisplayFormat(displayFormat);
      }
    }

    catch (Exception e) {
      // If anything goes wrong, we will see a stack trace.
      e.printStackTrace();
    }

    finally {
      // we have (hopefully) retrieved our data.  Tidy up and close the
      // database.
      if (database != null) try {
        database.closeRecordStore();
      }
      catch (Exception e) {
      }
    }
  }

  /**
   * <p>Save user preferences to database.</p>
   */
  private void saveOptions() {
    RecordStore preferencesDb  = null;
    try {
      // Remove the old preferences database to be sure that we save a clean
      // copy.  (overwriting it may not overwrite properly so we delete it
      // instead).
      RecordStore.deleteRecordStore(PREFERENCES_DATABASE);

      // Now create a fresh preferences database and store off our
      // user preferences.
      // (The openRecordStore() method creates a new database if it can't find
      // one with the given name.  Since we just deleted the old one, it will
      // just create a new database.)
      preferencesDb = RecordStore.openRecordStore(PREFERENCES_DATABASE, true);

      // Retrieve the currently selected display time format.
      int displayFormat = mainMenu.getDisplayFormat();

      // Store the display format as a string.
      // First, convert the display format to a string.
      String displayFormatString = String.valueOf(displayFormat);

      // Now, add it to the database.
      preferencesDb.addRecord(
        displayFormatString.getBytes(),         // The string bytes.
        0,                                      // Record offset.
        displayFormatString.getBytes().length); // Number of bytes to store.
    }

    catch (Exception e) {
      // If anything went wrong, we will get a stack trace.
      e.printStackTrace();
    }

    finally {
      // Close the database.
      if (preferencesDb != null) try {
        preferencesDb.closeRecordStore();
      }
      catch (Exception e1) {
      }
    }
  }


}