To Lecture Notes

IT 372 -- May 19, 2025

Review Questions

1. What is the difference between the Kotlin val and var keywords?
   Answer: a variable defined with val is a constant, whose value cannot be changed. A variable defined with var can be changed.
2. Define a Kotlin Animal class specified by this UML diagram:
   

   +----------------------------------------+
   |               Animal                   |
   +----------------------------------------+
   | - species    : String {get}            |
   | - age        : Int {get, set }         |
   | - vaccinated : Boolean {get, set}      | 
   +----------------------------------------+
   | + haveBirthday( )                      |
   | + vaccinate( )                         |
   | + toString( ) : String                 |
   +----------------------------------------+
   

   Answer:
   

   // Source code file: Animal.kt
   package it372.ssmith.testkotlin
   // species is defined with val so it only
   //     has an autogenerated getter.
   // age is defined with var, so it has
   //     an autogenerated getter and setter
   class Animal(val species : String, var age : Int) {
       var vaccinated = false;
   
       fun vaccinate( ) {
           vaccinated = true;
       }
   
       fun haveBirthday( ) {
           this.age++;
       }
   
       override fun toString(): String {
           return "$species; $age; $vaccinated"
       }
   }
   ---------------------------------------------
   // Source code file: Test1.kt
   package it372.ssmith.testkotlin
   fun main( ) {
       var animal1 = Animal("dog", 3);
       println(animal1)
       animal1.haveBirthday( );
       println(animal1.age)
       animal1.vaccinate( )
       println(animal1.vaccinated)
   }
   

3. Implement the Magic8Ball2 Example using Kotlin for the Prediction and MainActivity classes.
   activity_main.xml  Prediction.kt  MainActivity.kt

Introduction to Kotlin

• Look at these sections:
  Example 15: a Dog class with explicit getters and setters.

Project 5

• Look at the Project 5 Description: a Rock, Paper, Scissors Game

Review of SQL

• Start with this SQL table named kids:
  

  name	gender	age
  Alice	F	11
  Chloe	F	12
  William	M	9
  Scott	M	10
  Jason	M	12

  1. Write an SQL create statement that creates this table. Answer:
     

     create table kids(name text, gender text, age integer);
     

  2. Write an SQL insert statement that inserts the row (Alice, F, 11) into the table. Answer:
     

     insert into kids values('Alice', 'F', 11);
     

  3. Write an SQL select statement that shows the entire table.
     

     select * from kids;
     

  4. Write an SQL select statement that shows the name and age of all the girls.
     

     select name, age from kids where gender = 'F';
     

  5. Write an SQL select statement that shows the names of all the boys with age greater than or equal to 10.
     

     select name from kids where gender = 'M' and age >= 10;
     

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.