To Lecture Notes

IT 372 -- May 22, 2024

Review Questions

1. What is the difference between the Kotlin val and var keywords?
2. Define a Kotlin Point class specified by this UML diagram:
   

   +----------------------------------------+
   |                 Point                  |
   +----------------------------------------+
   | - x : Float {get}                      |
   | - y : Float {get}                      |
   +----------------------------------------+
   | + distanceFromOrigin( ) : Float        |
   | + equals(otherPoint : Point) : Boolean |
   | + toString( ) : Boolean                |
   +----------------------------------------+
   

   Answer: See Example 14 in the Introduction to Kotlin document.
3. Define Kotlin Animal and Pet classes with these instance variables:
   

   Animal: species  age  vaccinated
   Pet:    name   owner
   

   Pet inherits from Animal. Define toString methods for each class. Test each class.
   Answer: See Example 18 in the Introduction to Kotlin document.
4. Implement the ClickCounter Example in Kotlin.
   Answer:
5. Implement the Magic8Ball Example using Kotlin for the Prediction and MainActivity classes.

Introduction to Kotlin

• Look at examples 14 through 17.

Creating and Using SQL Tables in Android Apps

1. Create SQLite database.
   Define a class derived from SQLiteOpenHelper:
   

   public class SDBH extends SQLiteOpenHelper {
       public KidsDbHelper(Context context) {
           super(context, "kids2.db", null, 1);
       }
   
       @Override
       public void onCreate(SQLiteDatabase db) {
           // This method is only called if the database
           // Does not exist.
   
           // Recommendation: leave the body of this
           // method empty.  Put code for creating and
           // populating tables in the activity file.  
       }
   
       @Override
       public void onUpgrade(SQLiteDatabase db, 
           int i, int i1) {
           // We will not use this onUpgrade method 
           // in IT 372, but it is still required.
       }
   }
   

2. Create SQLite table in the activity file:
   

   SQLiteOpenHelper dbh = new KidsDbHelper(this);
   SQLiteDatabase db = dbh.getReadableDatabase( );
   db.execSQL("create table kids(name text, 
       gender text, age integer)");
   

3. Insert row into table:
   

   ContentValues studentValues = new ContentValues( );
   studentValues.put("name", name);
   studentValues.put("grade", grade);
   studentValues.put("gender", gender);
   db.insert("students", null, studentValues);
   

4. Create Cursor to view or use query results:
   

   Cursor cursor = db.query("students",
       new String[ ] {"name", "grade", "gender"},
       null, null, null, null, null);
   

   The five null arguments correspond to these parameters:
   

   selection  selectionArgs  groupBy  having  orderBy
   

   We will see how to use these arguments later.
5. Methods to position cursor within result set:
   

   cursor.moveToFirst( )
   cursor.moveToNext( )
   cursor.moveToPrevious( )
   cursor.moveToLast( )
   

6. Methods to obtain field values from current cursor position:
   

   cursor.getDouble(columnIndex)
   cursor.getInt(columnIndex)
   cursor.getString(columnIndex)
   

Practice Problems

1. Look at the StudentsDb1 Example.
2. Look at the StudentsDb2 Example.
3. KidsDb1 Example. Use this kids.txt file to populate a kids table in a database named kids.db.  Here is the table schema:
   

   name : text; gender : text; age : integer
   

   After the kids table has been populated, query the table to display all of its data concatenated in a single textview. Answer:
   Here are the files for the app: activity_main.xml   KidsDbHelper.java   MainActivity.java