Apr 15, 2026 -- Notes

IT 372 -- Apr 15, 2026

Review Questions

Translate these formulas into Java:

a = √(s + 3 t³ⁿ)
Answer:

double a = Math.sqrt(s + 3 * Math.pow(t, 3 * n));

2 s t¹⁺ⁿ

1 - 5(u + 2)²ⁿ

Answer:

double b = (2 * s * Math.pow(t * (1 + n)) / 
           (1 - 5 * Math(u + 2, 2 * n));

The following code copies the items from an arraylist declared by

ArrayList<Integer> al = new ArrayList<Integer>( );

into a string:

String output = "";
for(Integer n : al) {
    output += n + "\n";
}

Perform this operation using a StringBuilder collection instead. If there are many items in the arraylist, using a StringBuilder collection is much faster. Answer

// Declare ArrayList object and add items to it.
StringBuilder sb = new StringBuilder("");
String output = "";
for(Integer n : a1) {
    a1.append(n + "\n");
}

Add these strings to an ArrayList collection:

c  java  kotlin  python

Then use the ArrayList method replaceAll that accepts a lambda function to convert each of the strings to uppercase. Answer:

ArrayList<String> list = new ArrayList<String>( );
list.add("c");
list.add("java");
list.add("kotlin");
list.add("python");
list.replaceAll( s -> s.toUpperCase( ));
String output = "";
for(String s : list) {
    output += s + \n");
}
TextView tv = findViewById(R.id.txt_output);
tv.setText(output);

Create an Android app with four radio buttons with text Freshman, Sophomore, Junior, Senior. Place them in a radio button group. Add a button with text Show Year that shows the selected year using the codes 1, 2, 3, and 4. Answer: activity_main.xml MainActivity.java
What is an Android drop-down menu called?
Answer: it is called a Spinner.
Set up a spinner that contains the text Freshman, Sophomors, Junior, Senior. Add a button that displays the selected year using the codes 1, 2, 3, and 4.
Answer: strings.xml activity_main.xml MainActivity.java
How do you restrict the inputs to an EditText widget? For example, how do you set it up so that only numbers can be entered?
Answer: Set the inputType attribute in the EditText widget like this:
```
android:inputType="number"
or
android:inputType="numberSigned
or
android:inputType="numberDecimal"
```
How do you display special characters in a widget?-
Answer: You can't use HTML entities, but you can use Unicode characters. See the website unicode.org for code charts. For example, the unicode codes for the greek letters alpha (α), beta (β), gamma (γ) are 0BC1, 0BC2, and 0BC3. Here is an attribute that displays these Greek letters in a TextView widget:
```
android:text="Greek letters: \u03B1, \u03B2, \u03B3"
```

The Activity Lifecycle

We know about the onCreate method. It is a required method in every Android activity. What are some other Android lifecycle methods?
Look at this document from the Android Developer website:
Understand the Activity Lifecycle
The seven events in the activity lifecycle:
Create Start Resume Restart Pause Stop Destroy
An event handler is said to fire when it executes in response to its event occurring.

Event	Event Handler	Description	Required
ON_CREATE	onCreate	Fires immediately after the activity is first created.	Yes
ON_START	onStart	Fires immediately after the activity becomes visible. It prepares the activity to move into the foreground and become interactive.	No
ON_RESUME	onResume	Fires when the activity becomes interactive after starting or restarting.	No
ON_RESTART	onRestart	Fires when a covered activity moves into the foreground after being stopped, but not destroyed.	No
ON_PAUSE	onPause	Fires immediately before the activity moves into the background. It may still be visible.	No
ON_STOP	onStop	Fires when the activity has finished running and is no longer visible to the user, but may still be in memory.	No
ON_DESTROY	onDestroy	Fires immediately before an app has terminated and is about to be unloaded from memory.	No

Transition Diagram of the Activity Lifecycle.
Event handlers are callback methods. They are not called in the activity code, but in the Android framework when the event occurs that corresponds to the event handler.
Callbacks epitomize the Hollywood Principle: "Don't call us, we'll call you."

Here is an automobile analogy to these lifecycle events. In this analogy, the "app" consists of driving a car from home to the office.

@Override
public void onCreate(...) {
    super.onCreate(...);
    openGarageDoor( );
    unlockCar( );
    getInCar( );
    closeCarDoor( );
    putOnSeatBelt( );
    putKeyInIgnition( );
}

@Override
public void onStart( ) {
    super.onStart( );
    startEngine( );
    changeRadioStation( );
    switchOnLightsIfNeeded( );
    switchOnWipersIfNeeded( );
}

@Override
public void onResume( ) {
    super.onResume( );
    applyFootbrake( );
    releaseHandbrake( );
    putCarInGear( );
    drive( );
}

@Override
public void onPause( ) {
    super.onPause( );
    putCarInNeutral( );
    applyHandbrake( );
}

@Override
public void onStop( ) {
    super.onStop( );
    switchOffLights( );
    switchOffRadio( );
    switchOffHeater( );
    turnOffEngine( );
    removeSeatBelt( );
    getOutOfCar( );
    lockCar( );
}

@Override
public void onDestroy( ) {
    super.onDestroy( );
    goToOfficeBuilding( );
}

@Override
protected void onRestart() {
    unlockCar( );
    getInCar( );
    closeCarDoor( );
    putOnSeatBelt( );
    putKeyInIgnition( );
}

Reference:
danielsaidi.com/blog/2013/08/05/android-activity-lifecycle-car-analogy

Create an app named Lifecycle methods. Add a print statement to the onCreate method:

 @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.i("OO1", "In onCreate method");
}

Add an onStart method with a print statement like this:

@Override
public void onStart() {
    super.onStart( );
    Log.i("OO1", "In onStart method");
}

Similarly add onResume and onPause methods.

Some Examples

Look at this example: BeerAdvisor