To Lecture Notes

IT 372 -- May 13, 2026

Review Exercises

1. How do you set the font size for the JPC Text and Textfield elements?

JetPack Compose Examples

• Look at JPCEx 9, 10, 12, 13, 14, 15, 16.
  

Practice Problems

1. Look at Views Example. Here are the source code files:
         activity_main.xml  MainActivity.java  theraven.txt
   Create a new raw folder in the res/values folder, then copy the raven.txt file to that folder.

More About the Any Class

• As we know, Any is the direct or indirect base class of every Kotlin class.
• The Any Kotlin class corresponds to the Object Java class.
• The Any class defines only three instance methods:
  
  1. equals(other : Any?) : boolean   checks for equality between two any objects: the this object and the other object.
     
  2. hashCode(): Int  returns a hash code value for the object, which is used in hash-based collections like Map, MutableMap, Set, MutableSet.
  3. toString( ) : String  returns a  String representation of the object, which, if not overridden, is the Class name and hex address of the object.
• Test this Kotlin source code using the Kotlin Playground webpage:
  

  // GroceryItem Class
  class GroceryItem(var description : String, var code : Int,
      var price : Double, var onSale : Boolean) {
  
      fun salePrice(discount : Double) : Double {
          return price * (100 - discount) / 100
      }
  }
  
  fun main( ) {
      // For the GroceryItem objects, since the methods
      // equals, hashCode, and toString are not overridden,
      // the methods are called directly from the Any class.
  
      // Create four GroceryItem objects.
      var gItem1 = GroceryItem("Cabbage", 45678, 1.29, false)
      var gItem2 = GroceryItem("Green Beans", 98765, 2.45, true)
      var gItem3 = GroceryItem("Cabbage", 45678, 1.29, false)
      var gItem4 = gItem2;
      
      // Test Any equals method.
      println("${gItem1.equals(gItem2)}")
      println("${gItem1.equals(gItem3)}")
      println("${gItem2.equals(gItem4)}")
      println( )
  
      // Test Any hashCode method.
      println("${gItem1.hashCode( )}")
      println("${gItem2.hashCode( )}")
      println("${gItem3.hashCode( )}")
      println("${gItem4.hashCode( )}")
      println( )
  
      // Test Any toString method.
      println("$gItem1")
      println("$gItem2")
      println("$gItem3")
      println("$gItem4")
  }
  

• What do you observe about the behavior of these Any functions.

Data Classes

• A data class is designed to hold data.
• Usually, data classes do not define many instance methods.
• Here is the GroceryItem class defined as a data class with no defined methods:
  

  data GroceryItem(var description : String, var code : Int,
      var price : Double, var onSale : Boolean) { }
  

Android Platform

• Some Details about the Android Platform.
• To view files on the virtual device, use the Device Explorer.