Mobile Software Engineering I - Unit 6

Question 1

What is the thread, given to each app’s process when initiated by the Android Runtime, called?

Answer 1

The main thread or UI thread.

Question 2

What main categories of threads exist in Android?

Answer 2

• attached to the life cycle of an activity
• not attached to any activity

Question 3

How long, at a maximum, does the Android development team advise a call to take on the main thread?

Answer 3

15 ms

Question 4

What different states can a thread be in?

Answer 4

• new
• runnable
• blocked/waiting
• terminated

Question 5

What Java class and/or interface (fully qualified name) can be used what created a new thread?

Answer 5

java.lang.Thread or java.lang.Runnable

Question 6

How can threads be terminated in Java?

Answer 6

Not directly, but through Thread.interrupt().

Question 7

What main reasons exist to use a message handler in java?

Answer 7

• perform something in the future
• perform something on another thread

Question 8

What methods can be used to schedule a message?

Answer 8

• post(Runnable)
• postDelayed(Runnable, long)
• sendMessage(Message)
• sendMessageAtTime(Message, long)

Question 9

What are the primary advantages of using a thread pool?

Answer 9

• improved performance when a large number of tasks are executed
• worker threads can be kept alive and reused
• life cycle of each thread is controlled by the thread pool overall life cycle

Question 10

What Java class is used to manage a thread pool?

Answer 10

ThreadPoolExecutor

Question 11

Does Android attempt to use all available RAM, as little RAM as possible, or something in between?

Answer 11

All available RAM.

Question 12

What main memory types are typically used in Android?

Answer 12

• RAM: limited in size but fast
• zRAM: a partition of RAM used for swap space
• storage: the file system

Question 13

What tool does Android Studio provide to analyse memory allocations?

Answer 13

Memory Profiler

Question 14

What is the meaning of the following types of memory allocations:

• allocations
• native size
• shallow size
• retained size

Answer 14

• allocations: number of allocation in the heap
• native size: native memory used by the object
• shallow size: Java memory used
• retained size: total size of memory allocated

Question 15

What alternative to services can be used to reduce the risk of a memory leak?

Answer 15

IntentService

Question 16

What is memory churn?

Answer 16

The rapid allocation of many temporary objects that cause a number of garbage collection events.

Question 17

What tools can be used to reduce the size of an APK file?

Answer 17

ProGuard and R8

Question 18

What type of exception is thrown if an application uses too much memory?

Answer 18

OutOfMemoryError

Question 19

What is the kswapd program, and what is it used for?

Answer 19

The kernal swap daemon is used to reduce the amount of used memory be converting used memory into free memory.

Question 20

What values can be passed to the onTrimMemory() method, and what do they mean?

Answer 20

• TRIM_MEMORY_RUNNING_MODERATE: app is not under threat of being killed
• TRIM_MEMORY_RUNNING_LOW: app is not under threat of being killed
• TRIM_MEMORY_RUNNING_CRITICAL: the system will start killing apps
• TRIM_MEMORY_COMPLETE: the app is next in line to be killed