I have compiled a list of interview questions asked on Android.
Objective/Audience: Help Job aspirant who are seeking a job as Android developer to help them prepare better.
- Difference in activity and services
To answer this question you should have understanding of what activity and services do. Once you understand that it will be very easy to explain it.
For better understanding: https://stackoverflow.com/questions/5050005/what-is-the-difference-between-an-android-activity-and-service - Difference in Activity context Vs Application context
https://blog.mindorks.com/understanding-context-in-android-application-330913e32514 - How Android system Render/draw layout on screen
https://developer.android.com/guide/topics/ui/how-android-draws - Nested Recycler view and Nested Scroll view — advantage Vs disadvantage or issues
- Given an Android app which is very slow ,For ex — UI is lagging and user has to wait a lot to see data on screen. Or May be list view scroll is slow. Where should we start looking into to find the reason.
Approach: To answer this question you must know how UI rendering happens in android. For ex you can have thousands of item to show in list, but on phones at a time limited set of data is shown. So suppose you open the screen and then you try to load data and do some parsing on those data, you have to be a little smart while doing all these. If you process all data at once it will be performance heavy and will lead to bad User experience. In such cases you should use pagination or Android Paging library. To understand pagination check my post : https://medium.com/@thegraduateguy/pagination-with-recyclerview-in-android-2506c4d09a5c
Further you should avoid any long running operation on UI thread. - Issues with Async task
https://blog.danlew.net/2014/06/21/the-hidden-pitfalls-of-asynctask/ - Can we change UI from asynchronous task using application context
https://stackoverflow.com/questions/987072/using-application-context-everywhere - Design handler thread in java
To answer this one should know how handler thread works in Android. For more information about Handler Thread from Google docs and you can also refer my previous article at below link
https://medium.com/@thegraduateguy/understanding-handler-looper-and-handler-thread-5cd9bf444802
You can read about it more and then formulate your answer. - Activity Launch Modes
https://developer.android.com/guide/components/activities/tasks-and-back-stack#ManifestForTasks
https://inthecheesefactory.com/blog/understand-android-activity-launchmode/en - Activity/Fragment LifeCycle
Activity: https://developer.android.com/guide/components/activities/activity-lifecycle
Fragment: https://developer.android.com/guide/components/fragments - Difference between fragment transaction add and replace
https://stackoverflow.com/questions/24466302/basic-difference-between-add-and-replace-method-of-fragment/24466345 - Permission handling in Android
Reference: https://developer.android.com/training/permissions/requesting - Difference in Service and Intent Service
https://www.linkedin.com/pulse/service-vs-intentservice-android-anwar-samir/ - Options in Android to do long running task.
Ans: Handler thread, Async task, Services ,Traditional Java threads
Be careful while using services as by default it runs on main thread so to do any long running task one must create a separate thread within service, - Does activity instance gets garbage collected after rotation . If activity reference is in AsyncTask , will it cause null pointer after rotation?
Yes activity can get garbage collected if it’s recreated after rotation and there is no reference of it. If this is used as a weak reference it can cause null pointer exception - Does two activity has same UI thread ?
NO. There is only one UI thread in Android System. - Difference in UI thread Vs main thread in Android
https://stackoverflow.com/questions/3261370/is-main-thread-the-same-as-ui-thread - What changes with respect to services came in Android P and Android O
Ref: https://developer.android.com/about/versions/oreo/background - What are content provider ?
Ref: https://developer.android.com/guide/topics/providers/content-provider-basics - What is inter app communication in Android and how to achieve it ?
Inter app communication is way in android by which two app can communicate and/or send data to each other. Two preferred way to do it Content Provider and AIDL
For ex whenever we want to see contact detail of any user we can query contact app using content provider. - What is recycler view? How it works? What are it’s advantages over list view?
https://blog.mindorks.com/how-does-recyclerview-work-internally#:~:text=%20How%20does%20RecyclerView%20work%20internally%3F%20%201,scrapped%20views.%20The%20view%20which%20we...%20More%20 - Fragment commit vs commitNow method
https://medium.com/@bherbst/the-many-flavors-of-commit-186608a015b1#:~:text=commit%20%28%29%20and%20commitAllowingStateLoss%20%28%29%20are%20almost%20identical,saved%20its%20state%2C%20it%20will%20throw%20an%20IllegalStateException. - Android parceable vs serializable interface
Very good article: https://android.jlelse.eu/parcelable-vs-serializable-6a2556d51538
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