问当SQLiteOpenHelper onCreate方法被调用时？

EN

import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase;
import android.content.Context;
import android.database.Cursor;
import android.content.ContentValues;
import android.util.Log;

public class DatabaseHandler extends SQLiteOpenHelper {
    // Static Constants
    /*** Database details ***/
    // Database version
    private static final int DATABASE_VERSION           = 1;

    // Database name
    private static final String DATABASE_NAME           = "database_name";

    /*** Database Tables ***/
    /** Events **/
    // Event table
    private static final String TABLE_EVENT             = "event";

    // Event table columns
    private static final String COLUMN_EVENT_EID        = "_eid";

    private static final String COLUMN_EVENT_CREATION_DATE  = "creation_date";

    private static final String COLUMN_EVENT_TITLE      = "title";
    private static final String COLUMN_EVENT_ICON       = "icon";

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        Log.e("MyApp", "onCreate invoked");
        // Tables creation queries
        String CREATE_EVENT_TABLE = "create table " + TABLE_EVENT + "(" + COLUMN_EVENT_EID + " integer primary key, "
                + COLUMN_EVENT_CREATION_DATE + " text, "
                + COLUMN_EVENT_TITLE + " text, "
                + COLUMN_EVENT_ICON + " text)";

        // Creating tables
        db.execSQL(CREATE_EVENT_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.e("MyApp", "onUpgrade invoked");
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_EVENT);
    }
}

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DatabaseHandler db = new DatabaseHandler(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}