To Lecture Notes

IT 372 -- Apr 17, 2019

Review Questions

1. Translate these formulas into Java:
   
   1. a = √(s + 3 t³ⁿ)

   2. b

      =

      2 s t1 + n 1 - 5(u + 2)2n

      
      Answers:
      

      a = Math.sqrt(s + 2 * Math.pow(t, 3 * n)
      b = (2 * s * Math.pow(3 * n)) / (1 - 5 * Math(u + 2, 2 * n))
      

2. Suppose you have a hashmap collection:
   

   HashMap<String, Integer> map = new HashMap<String, Integer>( )
   

   How do you add an Integer object to the collection? How do you retrieve the Integer object stored using the key "K123"? We will use a similar concept when we store information from an activity in the storedInstanceState object. Ans:
   

   // Put the value 35 into the Hashmap using the key "C123".
   map.put("C123", 35);
   // Retrieve the value stored at the key "C123" from the hashmap.
   int n = String.valueOf(map.get("C123"));
   

3. How do you allow the text in a button to include lowercase letters?
   Ans: include this attribute:
   

   android:textAllCaps="false"
   

4. Where do you place the image that is used for the background image in a layout?
   Ans: In the app/src/main/res/drawable folder
5. Explain the difference between android:gravity and android:layout-gravity.
   Ans: gravity determines where the contents of the widget are positioned. layout_gravity determines where the widget is positioned within its parent.
6. How do you get the text out of an EditText widget?
   

   EditText editText1 = (EditText) findViewById(R.id.edittext1);
   String s = editText1.getText( ).toString( );
   

TempConverter Project

• Look at the InnerClass Example.
• Look at methods 2 and 3 of the TempConverter Project.

The Activity Lifecycle

• Look at this document from the Android Developer website:
      Understanding the Activity Lifecycle
• The six important events in the activity lifecycle:
  onCreate onStart onResume onPause onStop onDestroy
• 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 moves into the foreground after going into the background.	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 a diagram of
• ClickCounter Example.