To Lecture Notes

IT 372 -- Apr 8, 2026

Review Exercises

1. What does the Android R class do?
   Answer: It manages the resources in an Android app, for example: ids defined in the layout file, colors in the colors.xml file and strings in the strings.xml file. You can use the id to create a Java object like this:
   

   TextView tv = findViewById(R.id.txt_temp);
   

2. Show how display a string dynamically from the strings.xml resource file. Answer:

   TextView tv = findViewById(R.id.txt_name);
   tv.setText(getString(R.string.first_name));
   

3. Show how to change a color dynamically from the colors.xml resource file. Answer:
   

   LinearLayout layout = findViewById(R.id.main);
   layout.setBackgroundColor(getColor(R.color.purple));
   // or
   layout.setBackgroundColor(0xFFFF00FF);
   

4. How do you change the int value n to the String value s? Answer:
   

   String s = String.valueOf(n);
   // or
   String s = n + "";
   // or
   String s = String.format(n, "%d");
   

5. Change this TempDesc class so that it has the instance variable temperature, the getter getTemperature, the setter setTemperature, and the method getDescriptor, Also include a parameterized constructor that initializes the instance variable. Use this UML diagram:
   

   +--------------------------------+
   |            TempDesc            |
   +--------------------------------+
   | - temperature : double         |
   +--------------------------------+
   | + TempDesc(temp: double)       |
   | + getTemperature( ) : double   |
   | + setTemperature(temp : double)|
   | + getDescriptor( ) : String    |
   +--------------------------------+
   

   Test your TempDesc class like this:
   

   double[ ] temps = {-13.0, 27.0, 52.0, 68.0, 87.0, 103.0};
   TempDesc tempObj = new TempDesc(0);
   String output = "";
   for(double temp : temps) {
       tempObj.setTemperature(temp);
       output += tempObj.getDescriptor( ) + "\n";
   }
   // Display the output variable contents
   // in a TextView widget:
   tv.setText(output);
   

   Then display the output in a TextView widget in an Android app.
   Answer: activity_main.xml   MainActivity.java   TempDescriptor.java
6. Translate this Java function to Kotlin:
   

   public static String makeGreeting(String name) {
       return "Hello, " + name + ", how are you?
   }
   

   Then test it by placing these lines at the end of the onCreate method in an app with language set to Kotlin:
   

   Log.i("001", makeGreeting("Larry"))
   

   View the output in the Logcat window. Answer:
   

   // The Kotlin translation of the makeGreeting function:
   
   fun makeGreeting(name: String) : String {
       return "Hello, $name, how are you?"
   }
   

   To pull up the Logcat Window, click the corresponding icon on the left of the Android Studio editor. (The Logcat icon looks like a cat face.) Replace package:mine by tag:001 and clear the Logcat window by right clicking and selecting Clear Logcat.

Magic8Ball Example

• Look at the Magic8Ball Example
• Convert the activity code for attaching the event listener from Method 1 to Method 4.

Project 1b

• Look at the Project 1b Description.

InnerClass Example

• An inner class is a class that is defined completely within another class.
• If an inner class is only used by the containing class, the accessibility of the inner class is often defined as private.
• Look at the InnerClass Example.
• Android event handlers can also be implemented with inner classes.
• The MyFrame class in the InnerClass Example shows how a Java Swing event handler is implemented.

A Simple Interface

• This example shows how to define and use a simple interface. On your computer, create a folder with files ManageOutput.java, A.java, and Main.java.  Then, from a Command Line (Windows) or Terminal (Mac) window, compile and run this project:
  

  > javac *.java
  > java Main
  

Android Event Handlers

• Android event handlers can also be implemented with inner classes.
• The details are in the TempConverter Example
• Method 1 is to use an onClick attribute, which is deprecated.
• Method 2 is to use an inner class to implement the click event handler.
• Method 3 is to use an anonymous inner class to implement the click event handler.
• Method 4 (recommended method) is use the setOnClickListener method an anonymous event handler method.
• The View.OnClickListener class is an inner interface of the View class.

Project 2

• Look at Project 2.

Using Images

• Setting a background image:
  
  • Copy the background image, for example, image1.jpg into the app/res/drawable folder.
  • Add this attribute to the layout or widget:
    

    android:background="@drawable/image1"
    

• This attribute can be used to crop the background image so that it fits the layout:
  

  android:scaleType="centerCrop"
  

The Design Editor

• The Design Editor is an alternative to directly editing the XML code that defines an Android layout.
• Use the Design editor to convert the default ConstraintLayout to a LinearLayout:
  Using the Design Editor, in the Component Tree,
  Right click on ConstraintLayout >>
  Select Convert view... >>
  Select LinearLayout to Convert View to: LinearLayout >>
  Click Apply.
• Use the Design Editor to drag five widgets onto a LinearLayout:
       TextView  Button  CheckBox  RadioButton  Switch
• Use the Design Editor to set these attributes of the widgets:
       id  text  layout_marginLeft   layout_marginTop
• The layout file and screen shot of the UseDesignEditor app that we worked on in class:
  activity_main.xml   Screen Shot
• Use the Design Editor to create an app that converts a Celsius temperature into Fahrenheit. Enter the Celsius temperature into an EditText widget and show the Fahrenheit temperature in a TextView widget when a button is clicked.
  Ans: See the TempConverter Example.