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└── README.md
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/README.md:
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1 | # Droid-Interview-Questions-
2 | Interview Questions on android Credit mindorks .
3 |
4 |
5 | ## A complete guide for learning Android Development
6 |
7 | ## Contents
8 |
9 | * [Core Android](#core-android)
10 | * [Android Libraries](#android-libraries)
11 | * [Android Architecture](#android-architecture)
12 | * [Android Design Problem](#android-design-problem)
13 | * [Android Unit Testing](#android-unit-testing)
14 | * [Android Tools And Technologies](#android-tools-and-technologies)
15 | * [Java and Kotlin](#java-and-kotlin)
16 | * [Data Structures And Algorithms](#data-structures-and-algorithms)
17 | * [Other Topics](#other-topics)
18 |
19 | ### Core Android
20 |
21 | #### Base
22 |
23 | * **Tell all the Android application components.** - [Learn from here](https://developer.android.com/guide/components/fundamentals.html#Components)
24 |
25 | * **What is the project structure of an Android Application?** - [Learn from here](https://developer.android.com/studio/projects)
26 |
27 | * **What is `Context`? How is it used?** - [Learn from here](https://blog.mindorks.com/understanding-context-in-android-application-330913e32514)
28 |
29 | * **What is `AndroidManifest.xml`?** - [Learn from here](https://developer.android.com/guide/topics/manifest/manifest-intro)
30 |
31 | * **What is `Application` class?**
32 | - The Application class in Android is the base class within an Android app that contains all other components such as activities and services. The Application class, or any subclass of the Application class, is instantiated before any other class when the process for your application/package is created.
33 |
34 | #### Activity and Fragment
35 |
36 | * **What is `Activity` and its lifecycle?** - [Learn from here](https://www.youtube.com/watch?v=RiFui-i-s-o)
37 |
38 | * **What is the difference between onCreate() and onStart()** - [Learn from here](https://www.youtube.com/watch?v=RiFui-i-s-o)
39 |
40 | * **When only onDestroy is called for an activity without onPause() and onStop()?** - [Learn from here](https://www.youtube.com/watch?v=QSxcLnZ1-RU)
41 |
42 | * **Why do we need to call setContentView() in onCreate() of Activity class?** - [Learn from here](https://www.youtube.com/watch?v=zeYK8JdMOi8)
43 |
44 | * **What is onSavedInstanceState() and onRestoreInstanceState() in activity?**
45 | - onSavedInstanceState() - This method is used to store data before pausing the activity.
46 | - onRestoreInstanceState() - This method is used to recover the saved state of an activity when the activity is recreated after destruction. So, the onRestoreInstanceState() receive the bundle that contains the instance state information.
47 |
48 | * **What is `Fragment` and its lifecycle.** - [Learn from here](https://blog.mindorks.com/android-fragments-and-its-lifecycle)
49 |
50 | * **What are "launch modes"?** - [Learn from here](https://blog.mindorks.com/android-activity-launchmode-explained-cbc6cf996802)
51 |
52 | * **What is the difference between a `Fragment` and an `Activity`? Explain the relationship between the two.** - [Learn from here](https://stackoverflow.com/questions/10478233/why-fragments-and-when-to-use-fragments-instead-of-activities)
53 |
54 | * **When should you use a Fragment rather than an Activity?**
55 | - When you have some UI components to be used across various activities
56 | - When multiple view can be displayed side by side just like viewPager
57 |
58 | * **What is the difference between FragmentPagerAdapter vs FragmentStatePagerAdapter?**
59 | - FragmentPagerAdapter: Each fragment visited by the user will be stored in the memory but the view will be destroyed. When the page is revisited, then the view will be created not the instance of the fragment.
60 | - FragmentStatePagerAdapter: Here, the fragment instance will be destroyed when it is not visible to the user, except the saved state of the fragment.
61 |
62 | * **What is the difference between adding/replacing fragment in backstack?** - [Learn from here](https://stackoverflow.com/questions/24466302/basic-difference-between-add-and-replace-method-of-fragment/24466345)
63 |
64 | * **Why is it recommended to use only the default constructor to create a `Fragment`?** - [Learn from here](https://www.youtube.com/watch?v=9EdvcycKP9A)
65 |
66 | * **How would you communicate between two Fragments?** - [Learn from here](https://blog.mindorks.com/how-to-communicate-between-fragments)
67 |
68 | * **What is retained `Fragment`?**
69 | - By default, Fragments are destroyed and recreated along with their parent Activity’s when a configuration change occurs. Calling setRetainInstance(true) allows us to bypass this destroy-and-recreate cycle, signaling the system to retain the current instance of the fragment when the activity is recreated.
70 |
71 | * **What is the purpose of `addToBackStack()` while commiting fragment transaction?**
72 | - By calling addToBackStack(), the replace transaction is saved to the back stack so the user can reverse the transaction and bring back the previous fragment by pressing the Back button. For more [Learn from here](https://stackoverflow.com/questions/22984950/what-is-the-meaning-of-addtobackstack-with-null-parameter)
73 |
74 | #### Views and ViewGroups
75 |
76 | * **What is `View` in Android?** - [Learn from here](https://blog.mindorks.com/android-user-interface-view-components)
77 |
78 | * **Difference between `View.GONE` and `View.INVISIBLE`?** - [Learn from here](https://stackoverflow.com/questions/11556607/android-difference-between-invisible-and-gone)
79 |
80 | * **Can you a create custom view? How?** - [Learn from here](https://blog.mindorks.com/create-your-own-custom-view)
81 |
82 | * **What are ViewGroups and how they are different from the Views?**
83 | - View: View objects are the basic building blocks of User Interface(UI) elements in Android. View is a simple rectangle box which responds to the user’s actions. Examples are EditText, Button, CheckBox etc. View refers to the android.view.View class, which is the base class of all UI classes.
84 | - ViewGroup: ViewGroup is the invisible container. It holds View and ViewGroup. For example, LinearLayout is the ViewGroup that contains Button(View), and other Layouts also. ViewGroup is the base class for Layouts.
85 |
86 | * **What is a Canvas?** - [Learn from here](https://blog.mindorks.com/understanding-canvas-api-in-android)
87 |
88 | * **What is a `SurfaceView`?** - [Learn from here](https://developer.android.com/reference/android/view/SurfaceView)
89 |
90 | * **Relative Layout vs Linear Layout.** - [Learn from here](https://blog.mindorks.com/android-layout-relative-linear-frame)
91 |
92 | * **Tell about Constraint Layout** - [Learn from here](https://blog.mindorks.com/using-constraint-layout-in-android-531e68019cd)
93 |
94 | * **Do you know what is the view tree? How can you optimize its depth?** - [Learn from here](https://developer.android.com/reference/android/view/ViewTreeObserver)
95 |
96 | * **How does the Touch Control and Events work in Android?** - [Learn from here](https://blog.mindorks.com/touch-control-and-events-in-android) and [here](https://www.youtube.com/watch?v=tKeYr7iV5xE)
97 |
98 | #### Displaying Lists of Content
99 |
100 | * **What is the difference between `ListView` and `RecyclerView`?** - [Learn from here](https://stackoverflow.com/questions/26728651/recyclerview-vs-listview)
101 |
102 | * **How does RecyclerView work internally?** - [Learn from here](https://blog.mindorks.com/how-does-recyclerview-work-internally) and [here](https://www.youtube.com/watch?v=60IYWdnHsZI)
103 |
104 | * **What is the ViewHolder pattern? Why should we use it?** - [Learn from here](https://stackoverflow.com/questions/21501316/what-is-the-benefit-of-viewholder-pattern-in-android)
105 |
106 | * **RecyclerView Optimization - Scrolling Performance Improvement** - [Learn from here](https://blog.mindorks.com/recyclerview-optimization)
107 |
108 | * **What is `SnapHelper`?** - [Learn from here](https://blog.mindorks.com/using-snaphelper-in-recyclerview-fc616b6833e8)
109 |
110 | #### Dialogs and Toasts
111 |
112 | * **What is `Dialog` in Android?** - [Learn from here](https://developer.android.com/guide/topics/ui/dialogs)
113 |
114 | * **What is `Toast` in Android?** - [Learn from here](https://developer.android.com/guide/topics/ui/notifiers/toasts)
115 |
116 | * **What the difference between `Dialog` and `Dialog Fragment`?** - [Learn from here](https://stackoverflow.com/questions/7977392/android-dialogfragment-vs-dialog)
117 |
118 | #### Intents and Broadcasting
119 |
120 | * **What is `Intent`?** - [Learn from here](https://blog.mindorks.com/what-are-intents-in-android)
121 |
122 | * **What is an Implicit `Intent`?** - [Learn from here](https://blog.mindorks.com/what-are-intents-in-android)
123 |
124 | * **What is an Explicit `Intent`?** - [Learn from here](https://blog.mindorks.com/what-are-intents-in-android)
125 |
126 | * **What is a `BroadcastReceiver`?** - [Learn from here](https://developer.android.com/guide/components/broadcasts)
127 |
128 | * **What is a `LocalBroadcastManager`?** - [Learn from here](https://blog.mindorks.com/using-localbroadcastmanager-in-android)
129 |
130 | * **What is the function of an `IntentFilter`?** - [Learn from here](https://developer.android.com/reference/android/content/IntentFilter)
131 |
132 | * **What is a Sticky `Intent`?**
133 | - Sticky Intents allows communication between a function and a service. sendStickyBroadcast() performs a sendBroadcast(Intent) known as sticky, i.e. the Intent you are sending stays around after the broadcast is complete, so that others can quickly retrieve that data through the return value of registerReceiver(BroadcastReceiver, IntentFilter). For example, if you take an intent for ACTION_BATTERY_CHANGED to get battery change events: When you call registerReceiver() for that action — even with a null BroadcastReceiver — you get the Intent that was last Broadcast for that action. Hence, you can use this to find the state of the battery without necessarily registering for all future state changes in the battery.
134 |
135 | * **Describe how broadcasts and intents work to be able to pass messages around your app?** - [Learn from here](https://stackoverflow.com/questions/7276537/using-a-broadcast-intent-broadcast-receiver-to-send-messages-from-a-service-to-a)
136 |
137 | * **What is a `PendingIntent`?**
138 | - If you want someone to perform any Intent operation at future point of time on behalf of you, then we will use Pending Intent.
139 |
140 | * **What are the different types of Broadcasts?** - [Learn from here](https://developer.android.com/guide/components/broadcasts)
141 |
142 | #### Services
143 |
144 | * **What is `Service`?** - [Learn from here](https://developer.android.com/guide/components/services)
145 |
146 | * **`Service` vs `IntentService`.** - [Learn from here](https://blog.mindorks.com/service-vs-intentservice-in-android)
147 |
148 | * **What is a `JobScheduler`?** - [Learn from here](https://developer.android.com/reference/android/app/job/JobScheduler)
149 |
150 | #### Inter-process Communication
151 |
152 | * **How can two distinct Android apps interact?** - [Learn from here](https://developer.android.com/training/basics/intents)
153 |
154 | * **Is it possible to run an Android app in multiple processes? How?** - [Learn from here](https://stackoverflow.com/questions/6567768/how-can-an-android-application-have-more-than-one-process)
155 |
156 | * **What is AIDL? Enumerate the steps in creating a bounded service through AIDL.** - [Learn from here](https://developer.android.com/guide/components/aidl)
157 |
158 | * **What can you use for background processing in Android?** - [Learn from here](https://developer.android.com/guide/background)
159 |
160 | * **What is a `ContentProvider` and what is it typically used for?** - [Learn from here](https://developer.android.com/guide/topics/providers/content-provider-basics) and [here](https://developer.android.com/guide/topics/providers/content-providers)
161 |
162 | #### Long-running Operations
163 |
164 | * **How to run parallel tasks in Java or Android, and get callback when all complete?** - [Learn from here](https://www.youtube.com/watch?v=v0ZSnISeyKE)
165 |
166 | * **Why should you avoid to run non-ui code on the main thread?** - [Learn from here](https://developer.android.com/training/multiple-threads/communicate-ui)
167 |
168 | * **What is ANR? How can the ANR be prevented?** - [Learn from here](https://developer.android.com/topic/performance/vitals/anr.html)
169 |
170 | * **What is an `AsyncTask`(Deprecated in API level 30) ?** - [Learn from here](https://www.youtube.com/watch?v=ZZ-6nGbfVdA)
171 |
172 | * **What are the problems in AsyncTask?** - [Learn from here](https://www.youtube.com/watch?v=ZZ-6nGbfVdA)
173 |
174 | * **When would you use java thread instead of an AsyncTask?** - [Learn from here](https://stackoverflow.com/questions/18480206/asynctask-vs-thread-in-android)
175 |
176 | * **What is a `Loader`? (Deprecated)** - [Learn from here](https://developer.android.com/guide/components/loaders)
177 |
178 | * **What is the relationship between the life cycle of an `AsyncTask` and an `Activity`? What problems can this result in? How can these problems be avoided?**
179 | - An AsyncTask is not tied to the life cycle of the Activity that contains it. So, for example, if you start an AsyncTask inside an Activity and the user rotates the device, the Activity will be destroyed (and a new Activity instance will be created) but the AsyncTask will not die but instead goes on living until it completes.
180 |
181 | - Then, when the AsyncTask does complete, rather than updating the UI of the new Activity, it updates the former instance of the Activity (i.e., the one in which it was created but that is not displayed anymore!). This can lead to an Exception (of the type java.lang.IllegalArgumentException: View not attached to window manager if you use, for instance, findViewById to retrieve a view inside the Activity).
182 |
183 | - There’s also the potential for this to result in a memory leak since the AsyncTask maintains a reference to the Activity, which prevents the Activity from being garbage collected as long as the AsyncTask remains alive.
184 |
185 | - For these reasons, using AsyncTasks for long-running background tasks is generally a bad idea . Rather, for long-running background tasks, a different mechanism (such as a service) should be employed.
186 |
187 | - Note: AsyncTasks by default run on a single thread using a serial executor, meaning it has only 1 thread and each task runs one after the other.
188 |
189 | * **Explain `Looper`, `Handler` and `HandlerThread`.** - [Learn from here](https://blog.mindorks.com/android-core-looper-handler-and-handlerthread-bd54d69fe91a) and [from video](https://www.youtube.com/watch?v=rfLMwbOKLRk&list=PL6nth5sRD25hVezlyqlBO9dafKMc5fAU2)
190 |
191 | * **How does the threading work in Android?** - [Learn from here](https://www.youtube.com/watch?v=zfDYK-xB1Uo)
192 |
193 | * **Android Memory Leak and Garbage Collection** - [Learn from here](https://www.youtube.com/watch?v=zCSSFRRIreo)
194 |
195 | #### Working With Multimedia Content
196 |
197 | * **How do you handle bitmaps in Android as it takes too much memory?** - [Learn from here](https://developer.android.com/topic/performance/graphics/load-bitmap) and [here](https://developer.android.com/topic/performance/graphics/manage-memory)
198 |
199 | * **What is the difference between a regular `Bitmap` and a nine-patch image?**
200 | - In general, a Nine-patch image allows resizing that can be used as background or other image size requirements for the target device. The Nine-patch refers to the way you can resize the image: 4 corners that are unscaled, 4 edges that are scaled in 1 axis, and the middle one that can be scaled into both axes.
201 |
202 | * **Tell about the `Bitmap` pool.** - [Learn from here](https://blog.mindorks.com/how-to-use-bitmap-pool-in-android-56c71a55533c)
203 |
204 | * **How to play sounds in Android?** - [Learn from here](https://blog.mindorks.com/using-mediaplayer-to-play-an-audio-file-in-android)
205 |
206 | * **How image compression is preformed?** - [Learn from here](https://blog.mindorks.com/understanding-image-compression-in-android)
207 |
208 | #### Data Saving
209 |
210 | * **How to persist data in an Android app?** - [Learn from here](https://blog.mindorks.com/android-shared-preferences-in-kotlin)
211 |
212 | * **What is ORM? How does it work?** - [Learn from here](https://www.youtube.com/watch?v=9OHzXUo3Ymk)
213 |
214 | * **How would you preserve `Activity` state during a screen rotation?** - [Learn from here](https://stackoverflow.com/questions/3915952/how-to-save-state-during-orientation-change-in-android-if-the-state-is-made-of-m)
215 |
216 | * **What are different ways to store data in your Android app?** - [Learn from here](https://blog.mindorks.com/understanding-storage-system-to-store-data-in-android)
217 |
218 | * **Explain Scoped Storage in Android.** - [Learn from here](https://blog.mindorks.com/understanding-the-scoped-storage-in-android)
219 |
220 | * **How to encrypt data in Android?** - [Learn from here](https://blog.mindorks.com/how-to-encrypt-data-safely-on-device-and-use-the-androidkeystore)
221 |
222 | * **What is commit() and apply() in SharedPreferences?**
223 | - commit() returns a boolean value of success or failure immediately by writing data synchronously.
224 | - apply() is asynchronous and it won't return any boolean response. If you have an apply() outstanding and you are performing commit(), then the commit() will be blocked until the apply() is not completed.
225 |
226 | #### Look and Feel
227 |
228 | * **What is a `Spannable`?** - [Learn from here](https://medium.com/androiddevelopers/underspanding-spans-1b91008b97e4)
229 |
230 | * **What is a `SpannableString`?**
231 | - A SpannableString has immutable text, but its span information is mutable. Use a SpannableString when your text doesn't need to be changed but the styling does. Spans are ranges over the text that include styling information like color, heighliting, italics, links, etc
232 |
233 | * **What are the best practices for using text in Android?** - [Learn from here](https://blog.mindorks.com/best-practices-for-using-text-in-android)
234 |
235 | * **How to implement Dark mode in any application?** - [Learn from here](https://blog.mindorks.com/implementing-dark-mode-theme-in-android)
236 |
237 | * **How to generate dynamic colors based in image?** - [Learn from here](https://blog.mindorks.com/color-palette-in-android)
238 |
239 | * **Explain about Density Independence Pixel** - [Learn from here](https://blog.mindorks.com/understanding-density-independent-pixel-sp-dp-dip-in-android)
240 |
241 | #### Memory Optimizations
242 |
243 | * **What is the `onTrimMemory()` method?** - [Learn from here](https://developer.android.com/topic/performance/memory)
244 |
245 | * **How does the OutOfMemory happens?** - [Learn from here](https://blog.mindorks.com/practical-guide-to-solve-out-of-memory-error-in-android-application)
246 |
247 | * **How do you find memory leaks in Android applications?** - [Learn from here](https://blog.mindorks.com/practical-guide-to-solve-out-of-memory-error-in-android-application) and [here](https://mindorks.com/blog/detecting-and-fixing-memory-leaks-in-android)
248 |
249 | #### Battery Life Optimizations
250 |
251 | * **How to reduce battery usage in an android application?** - [Learn from here](https://blog.mindorks.com/battery-optimization-for-android-apps-f4ef6170ff70)
252 |
253 | * **What is Doze? What about App Standby?** - [Learn from here](https://developer.android.com/training/monitoring-device-state/doze-standby)
254 |
255 | * **What is `overdraw`?** - [Learn from here](https://developer.android.com/topic/performance/rendering/overdraw.html)
256 |
257 | #### Supporting Different Screen Sizes
258 |
259 | * **How do you support different types of resolutions?** - [Learn from here](https://developer.android.com/training/multiscreen/screensizes)
260 |
261 | #### Permissions
262 |
263 | * **What are the different protection levels in permission?** - [Learn from here](https://blog.mindorks.com/what-are-the-different-protection-levels-in-android-permission)
264 |
265 | #### Native Programming
266 |
267 | * **What is the NDK and why is it useful?** - [Learn from here](https://www.youtube.com/watch?v=iljxHVt7Arc) and [here](https://blog.mindorks.com/getting-started-with-android-ndk-android-tutorial) and [here](https://www.youtube.com/watch?v=iljxHVt7Arc)
268 |
269 | * **What is renderscript?** - [Learn from here](https://blog.mindorks.com/comparing-android-ndk-and-renderscript-1a718c01f6fe)
270 |
271 | #### Android System Internal
272 |
273 | * **What is the Dalvik Virtual Machine?** - [Learn from here](https://blog.mindorks.com/what-are-the-differences-between-dalvik-and-art)
274 |
275 | * **What is the difference JVM, DVM and ART?** - [Learn from here](https://android.jlelse.eu/closer-look-at-android-runtime-dvm-vs-art-1dc5240c3924)
276 |
277 | * **What are the differences between Dalvik and ART?** - [Learn from here](https://blog.mindorks.com/what-are-the-differences-between-dalvik-and-art)
278 |
279 | * **What is DEX?** - [Learn from here](https://developer.android.com/reference/dalvik/system/DexFile)
280 |
281 | * **Can you manually call the Garbage collector?** - [Learn from here](https://stackoverflow.com/questions/15632734/can-we-call-the-garbage-collector-explicitly)
282 |
283 | #### Android Jetpack
284 |
285 | * **What is Android Jetpack and why to use this?** - [Learn from here](https://blog.mindorks.com/what-is-android-jetpack-and-why-should-we-use-it)
286 |
287 | * **What are Android Architecture Components?** - [Learn from here](https://blog.mindorks.com/what-are-android-architecture-components)
288 |
289 | * **What is LiveData in Android?** - [Learn from here](https://blog.mindorks.com/understanding-livedata-in-android)
290 |
291 | * **How LiveData is different from ObservableField?** - [Learn from here](https://blog.mindorks.com/livedata-vs-observable-in-android)
292 |
293 | * **What is the difference between setValue and postValue in LiveData?** - [Learn from here](https://blog.mindorks.com/livedata-setvalue-vs-postvalue-in-android)
294 |
295 | * **How to share ViewModel between Fragments in Android?** - [Learn from here](https://blog.mindorks.com/shared-viewmodel-in-android-shared-between-fragments)
296 |
297 | * **Explain Work Manager in Android.** - [Learn from here](https://blog.mindorks.com/integrating-work-manager-in-android)
298 |
299 | * **Use-cases of WorkManager in Android.** - [Learn from here](https://www.youtube.com/watch?v=4LTpYXFMnJw)
300 |
301 | * **How ViewModel work internally?** - [Learn from here](https://blog.mindorks.com/android-viewmodels-under-the-hood)
302 |
303 | #### Others
304 |
305 | * **Why Bundle class is used for data passing and why cannot we use simple Map data structure?** - [Learn from here](https://developer.android.com/guide/components/activities/parcelables-and-bundles)
306 |
307 | * **How do you troubleshoot a crashing application?** - [Learn from here](https://developer.android.com/topic/performance/vitals/crash)
308 |
309 | * **Explain Android notification system?** - [Learn from here](https://blog.mindorks.com/how-to-increase-push-notification-delivery-rate-in-android)
310 |
311 | * **What is the difference between Serializable and Parcelable? Which is the best approach in Android?** - [Learn from here](https://android.jlelse.eu/parcelable-vs-serializable-6a2556d51538)
312 |
313 | * **What is AAPT?** - [Learn from here](https://developer.android.com/studio/command-line/aapt2)
314 |
315 | * **What is the best way to update the screen periodically?** - [Learn from here](https://stackoverflow.com/questions/5452394/best-way-to-perform-an-action-periodically-while-an-app-is-running-handler)
316 |
317 | * **FlatBuffers vs JSON.** - [Learn from here](https://blog.mindorks.com/why-consider-flatbuffer-over-json-2e4aa8d4ed07)
318 |
319 | * **`HashMap`, `ArrayMap` and `SparseArray`** - [Learn from here](https://blog.mindorks.com/android-app-optimization-using-arraymap-and-sparsearray-f2b4e2e3dc47)
320 |
321 | * **What are Annotations?** - [Learn from here](https://blog.mindorks.com/creating-custom-annotations-in-android-a855c5b43ed9), [Link](https://blog.mindorks.com/improve-your-android-coding-through-annotations-26b3273c137a), [and from video](https://www.youtube.com/watch?v=LEb9if2HHSw)
322 |
323 | * **How to create custom Annotation?** - [Learn from here](https://blog.mindorks.com/creating-custom-annotations-in-android-a855c5b43ed9) and [here](https://www.youtube.com/watch?v=LEb9if2HHSw)
324 |
325 | * **How to handle multi-touch in android?** - [Learn from here](https://developer.android.com/training/gestures/multi)
326 |
327 | * **How to implement XML namespaces?** - [Learn from here](https://developer.android.com/reference/javax/xml/namespace/NamespaceContext)
328 |
329 | * **What is the support library? Why was it introduced?** - [Learn from here](https://developer.android.com/topic/libraries/support-library)
330 |
331 | * **What is Android Data Binding?** - [Learn from here](https://developer.android.com/topic/libraries/data-binding/index.html)
332 |
333 | * **How to check if Software keyboard is visible or not?** - [Learn from here](https://blog.mindorks.com/how-to-check-the-visibility-of-software-keyboard-in-android)
334 |
335 | * **How to take screenshot in Android programmatically?** - [Learn from here](https://blog.mindorks.com/how-to-programmatically-take-a-screenshot-on-android)
336 |
337 | ### Android Libraries
338 |
339 | * **Explain OkHttp Interceptor** - [Learn from here](https://blog.mindorks.com/okhttp-interceptor-making-the-most-of-it)
340 |
341 | * **OkHttp - HTTP Caching - How caching work in Android** - [Learn from here](https://www.youtube.com/watch?v=D6dQn6pUQD0)
342 |
343 | * **Tell me something about RxJava.** - [Learn from here](https://blog.mindorks.com/a-complete-guide-to-learn-rxjava-b55c0cea3631)
344 |
345 | * **How will you handle error in RxJava?** - [Learn from here](https://blog.mindorks.com/error-handling-in-rxjava)
346 |
347 | * **FlatMap Vs Map Operator** - [Learn from here](https://medium.com/mindorks/rxjava-operator-map-vs-flatmap-427c09678784)
348 |
349 | * **When to use `Create` operator and when to use `fromCallable` operator of RxJava?** - [Learn from here](https://blog.mindorks.com/understanding-rxjava-create-and-fromcallable-operator)
350 |
351 | * **When to use `defer` operator of RxJava?** - [Learn from here](https://blog.mindorks.com/understanding-rxjava-defer-operator)
352 |
353 | * **How are Timer, Delay, and Interval operators used in RxJava?** - [Learn from here](https://blog.mindorks.com/understanding-rxjava-timer-delay-and-interval-operators)
354 |
355 | * **How to make two network calls in parallel using RxJava?** - [Learn from here](https://blog.mindorks.com/understanding-rxjava-zip-operator-with-example)
356 |
357 | * **Tell the difference between Concat and Merge.** - [Learn from here](https://blog.mindorks.com/rxjava-operator-concat-vs-merge)
358 |
359 | * **Explain Subject in RxJava?** - [Learn from here](https://blog.mindorks.com/understanding-rxjava-subject-publish-replay-behavior-and-async-subject-224d663d452f)
360 |
361 | * **What are the types of Observables in RxJava?** - [Learn from here](https://blog.mindorks.com/understanding-types-of-observables-in-rxjava-6c3a2d0819c8)
362 |
363 | * **How to implement EventBus with RxJava?** - [Learn from here](https://blog.mindorks.com/implementing-eventbus-with-rxjava-rxbus-e6c940a94bd8)
364 |
365 | * **How to implement search feature using RxJava in your application?** - [Learn from here](https://blog.mindorks.com/implement-search-using-rxjava-operators-c8882b64fe1d)
366 |
367 | * **How The Android Image Loading Library Glide and Fresco Works?** - [Learn from here](https://blog.mindorks.com/how-the-android-image-loading-library-glide-and-fresco-works-962bc9d1cc40)
368 |
369 | * **Difference between Schedulers.io() and Schedulers.computation() in RxJava.**
370 |
371 | * **Why do we use the Dependency Injection Framework like Dagger in Android?** - [Learn from here](https://blog.mindorks.com/why-do-we-use-the-dependency-injection-framework-in-android)
372 |
373 | * **How does the Dagger work?** - [Learn from here](https://blog.mindorks.com/android-annotation-processing-tutorial-part-1-a-practical-approach) and [here]((https://www.youtube.com/watch?v=Grzqz-B3NWU))
374 |
375 | * **What is Component in Dagger?** - [Learn from here](https://www.youtube.com/watch?v=Grzqz-B3NWU)
376 |
377 | * **What is Module in Dagger?** - [Learn from here](https://www.youtube.com/watch?v=Grzqz-B3NWU)
378 |
379 | * **How does the custom scope work in Dagger?**
380 |
381 | * **When to call dispose and clear on CompositeDisposable in RxJava?** - [Learn from here](https://stackoverflow.com/questions/47057885/when-to-call-dispose-and-clear-on-compositedisposable)
382 |
383 | * **What is Multipart Request in Networking?** - [Learn from here](https://www.youtube.com/watch?v=p7SiNT0q1I8)
384 |
385 | * **What is Flow in Kotlin?** - [Learn from here](https://blog.mindorks.com/what-is-flow-in-kotlin-and-how-to-use-it-in-android-project)
386 |
387 | ### Android Architecture
388 |
389 | * **Describe the architecture of your last app.**
390 |
391 | * **Describe MVP.** - [Learn from here](https://mindorks.com/course/android-mvp-introduction)
392 |
393 | * **Describe MVVM.** - [Learn from here](https://blog.mindorks.com/mvvm-architecture-android-tutorial-for-beginners-step-by-step-guide) and [here](https://www.youtube.com/watch?v=HJMZNF-tG-4)
394 |
395 | * **MVC vs MVP vs MVVM architecture.** - [Learn from here](https://blog.mindorks.com/mvc-mvp-mvvm-architecture-in-android)
396 |
397 | * **What is presenter?** - [Learn from here](https://mindorks.com/course/android-mvp-introduction)
398 |
399 | * **What is model?** - [Learn from here](https://mindorks.com/course/android-mvp-introduction)
400 |
401 | * **Describe MVC.** - [Learn from here](https://blog.mindorks.com/mvc-mvp-mvvm-architecture-in-android)
402 |
403 | * **Describe MVI** - [Learn from here](https://github.com/MindorksOpenSource/MVI-Architecture-Android-Beginners)
404 |
405 | * **Describe the repository pattern** - [Learn from here](https://blog.mindorks.com/android-mvp-architecture-extension-with-interactors-and-repositories-bd4b51972339)
406 |
407 | * **What is controller?** - [Learn from here](https://blog.mindorks.com/mvc-mvp-mvvm-architecture-in-android)
408 |
409 | * **Tell something about clean code** - [Learn from here](https://blog.mindorks.com/every-programmer-should-read-this-book-6755dedec78d)
410 |
411 | ### Android Design Problem
412 |
413 | * **Design Uber App.** - [Learn from here](https://github.com/MindorksOpenSource/ridesharing-uber-lyft-app)
414 |
415 | * **Design Facebook App.**
416 |
417 | * **Design Facebook Near-By Friends App.**
418 |
419 | * **Design WhatsApp.**
420 |
421 | * **Design SnapChat.**
422 |
423 | * **Design problems based on location based app.**
424 |
425 | * **How to build offline-first app? Explain the architecture.**
426 |
427 | * **Design LRU Cache.**
428 |
429 | * **Design File Downloader** - [Learn from here](https://github.com/MindorksOpenSource/PRDownloader)
430 |
431 | * **Design an Image Loading Library** - [Learn from here](https://medium.com/@maheswaranapk/android-create-your-own-image-loading-library-in-kotlin-diy-bc7be9f286c5)
432 |
433 | * **HTTP Request vs HTTP Long-Polling vs WebSockets** - [Learn from here](https://www.youtube.com/watch?v=k56H0DHqu5Y)
434 |
435 | ### Android Unit Testing
436 | * **What is Espresso?** - [Learn from here](https://developer.android.com/training/testing/ui-testing/espresso-testing.html)
437 |
438 | * **What is Robolectric?** - [Learn from here](http://robolectric.org/)
439 |
440 | * **What are the disadvantages of using Robolectric?** - [Learn from here](https://stackoverflow.com/questions/18271474/robolectric-vs-android-test-framework)
441 |
442 | * **What is UI-Automator?** - [Learn from here](https://developer.android.com/training/testing/ui-testing/uiautomator-testing.html)
443 |
444 | * **Explain unit test.** - [Learn from here](https://developer.android.com/training/testing/unit-testing/local-unit-tests)
445 |
446 | * **Explain instrumented test.** - [Learn from here](https://developer.android.com/training/testing/unit-testing/instrumented-unit-tests)
447 |
448 | * **Have you done unit testing or automatic testing?**
449 |
450 | * **Why Mockito is used?** - [Learn from here](http://site.mockito.org/)
451 |
452 | * **Describe JUnit test.** - [Learn from here](https://en.wikipedia.org/wiki/JUnit)
453 |
454 | * **Describe code coverage.** - [Learn from here](https://blog.mindorks.com/generate-global-code-coverage-report-in-android-development-using-jacoco-plugin)
455 |
456 | ### Android Tools And Technologies
457 |
458 | * **What is ADB?** - [Learn from here](https://developer.android.com/studio/command-line/adb)
459 |
460 | * **What is DDMS and what can you do with it?** - [Learn from here](https://developer.android.com/studio/profile/monitor)
461 |
462 | * **What is the StrictMode?** - [Learn from here](https://blog.mindorks.com/use-strictmode-to-find-things-you-did-by-accident-in-android-development-4cf0e7c8d997)
463 |
464 | * **What is Lint? What is it used for?** - [Learn from here](https://blog.mindorks.com/what-is-lint-what-is-it-used-for)
465 |
466 | * **Git.** - [Learn from here](https://www.youtube.com/watch?v=D4h8Dbrjt4M&list=PL6nth5sRD25itbyNVUULAebzL-VLrLfkK)
467 |
468 | * **Android Development Useful Tools.** - [Learn from here](https://blog.mindorks.com/android-development-useful-tools-fd73283e82e3)
469 |
470 | * **Firebase.** - [Learn from here](https://firebase.google.com/)
471 |
472 | * **How to measure method execution time in Android?** - [Learn from here](https://blog.mindorks.com/measure-method-execution-time-in-android-debug-build)
473 |
474 | * **Can you access your database of SQLite Database for debugging?** - [Learn from here](https://blog.mindorks.com/how-to-access-sqlite-database-in-android-for-debugging)
475 |
476 | * **What are things that we need to take care while using Proguard?** - [Learn from here](https://blog.mindorks.com/things-to-care-while-using-proguard-in-android-application)
477 |
478 | * **What is Multidex in Android?** - [Learn from here](https://blog.mindorks.com/understanding-multidex-in-android)
479 |
480 | * **How to use Android Studio Memory Profiler?** - [Learn from here](https://www.youtube.com/watch?v=FxDa2td6Ej8)
481 |
482 | * **How to use Firebase realtime database in your app?** - [Learn from here](https://blog.mindorks.com/firebase-realtime-database-android-tutorial)
483 |
484 | * **What is Gradle?** - [Learn from here](https://blog.mindorks.com/gradle-for-android-developers-getting-the-most-of-it)
485 |
486 | * **APK Size Reduction.** - [Learn from here](https://blog.mindorks.com/how-to-reduce-apk-size-in-android-2f3713d2d662) and [here](https://blog.mindorks.com/using-r8-to-reduce-apk-size-in-android)
487 |
488 | * **How can you speed up the Gradle build?** - [Learn from here](https://blog.mindorks.com/speed-up-gradle-build-for-android-to-save-your-time)
489 |
490 | * **About gradle build system.** - [Learn from here](https://blog.mindorks.com/gradle-for-android-developers-getting-the-most-of-it)
491 |
492 | * **About multiple apk for android application.** - [Learn from here](https://mindorks.com/blog/how-to-create-multiple-apk-files-for-android-application)
493 |
494 | * **What is proguard used for?** - [Learn from here](https://blog.mindorks.com/applying-proguard-in-an-android-application)
495 |
496 | * **What is obfuscation? What is it used for? What about minification?** - [Learn from here](https://www.youtube.com/watch?v=yduedsaxfDw)
497 |
498 | * **How to change some parameters in an app without app update?** - [Learn from here](https://blog.mindorks.com/getting-started-with-firebase-remote-config-in-android)
499 |
500 | ### Java and Kotlin
501 |
502 | #### OOP
503 |
504 | * **Explain OOP Concepts.**
505 | - Object-Oriented Programming is a methodology of designing a program using classes, objects,
506 | [inheritance](https://en.wikipedia.org/wiki/Inheritance_(object-oriented_programming)),
507 | [polymorphism](https://en.wikipedia.org/wiki/Polymorphism_(computer_science)),
508 | [abstraction](https://en.wikipedia.org/wiki/Abstraction_(software_engineering)), and
509 | [encapsulation](https://en.wikipedia.org/wiki/Encapsulation_(computer_programming)).
510 |
511 | * **What is the difference between a constructor and a method?**
512 | - The name of the constructor is same as that of the class name, whereas the name of the method can be anything.
513 | - There is no return type of a constructor.
514 | - When you make an object of a class, then the constructor of that class will be called automatically.
515 | But for methods, we need to call it explicitely.
516 | - Constructors can't be inherited but you can call the constructor of the parent class by calling `super()`.
517 | - Constructor and a method they both run a block of code but the difference is in calling them.
518 | - We can call method directly using their name.
519 | - Constructor Syntax -
520 | ```java
521 | public class SomeClassName{
522 | SomeClassName(parameter_list){
523 | ...
524 | }
525 | ...
526 | }
527 | ```
528 | - Note:
529 | In the above syntax, the name of the constructor is the same as that of class
530 | and it has no return type.
531 |
532 | - Method Syntax
533 | ```java
534 | public class SomeClassName{
535 | public void someMethodName(parameter_list){
536 | ...
537 | }
538 | // call method
539 | someMethodName(parameter_list)
540 | }
541 | ```
542 | * **Differences between abstract classes and interfaces?**
543 | - An abstract class, is a class that contains both concrete and abstract methods
544 | (methods without implementations). An abstract method must be implemented by the abstract class
545 | sub-classes. Abstract classes cannot be instantiated and need to be extended to be used.
546 | - An interface is like a blueprint/contract of a class (or it may be thought of as a class with methods, but without their implementation). It contains empty methods that
547 | represent, what all of its subclasses should have in common. The subclasses provide the
548 | implementation for each of these methods. Interfaces are implemented.
549 |
550 | * **What is the difference between iterator and enumeration in java?**
551 | - In Enumeration we don't have remove() method and we can only read and traverse through a collection.
552 | - Iterators can be applied to any collection. In Iterator, we can read and remove items from a collection.
553 |
554 | * **Do you agree we use composition over inheritance?** [Learn from here](https://www.journaldev.com/12086/composition-vs-inheritance)
555 |
556 | * **Difference between method overloading and overriding.**
557 |
558 |
559 |
560 | - Overloading happens at compile-time while Overriding happens at runtime: The binding of overloaded method call to its definition happens at compile-time however binding of overridden method call to its definition happens at runtime.
561 | More info on static vs. dynamic binding: [StackOverflow](https://stackoverflow.com/questions/19017258/static-vs-dynamic-binding-in-java).
562 | - Static methods can be overloaded which means a class can have more than one static method of same name. Static methods cannot be overridden, even if you declare a same static method in child class it has nothing to do with the same method of parent class as overridden static methods are chosen by the reference class and not by the class of the object.
563 |
564 | So, for example:
565 | ```java
566 | public class Animal {
567 | public static void testClassMethod() {
568 | System.out.println("The static method in Animal");
569 | }
570 |
571 | public void testInstanceMethod() {
572 | System.out.println("The instance method in Animal");
573 | }
574 | }
575 |
576 | public class Cat extends Animal {
577 | public static void testClassMethod() {
578 | System.out.println("The static method in Cat");
579 | }
580 |
581 | public void testInstanceMethod() {
582 | System.out.println("The instance method in Cat");
583 | }
584 |
585 | public static void main(String[] args) {
586 | Cat myCat = new Cat();
587 | myCat.testClassMethod();
588 | Animal myAnimal = myCat;
589 | myAnimal.testClassMethod();
590 | myAnimal.testInstanceMethod();
591 | }
592 | }
593 | ```
594 | Will output:
595 | ```java
596 | The static method in Cat // testClassMethod() is called from "Cat" reference
597 |
598 | The static method in Animal // testClassMethod() is called from "Animal" reference,
599 | // ignoring actual object inside it (Cat)
600 |
601 | The instance method in Cat // testInstanceMethod() is called from "Animal" reference,
602 | // but from "Cat" object underneath
603 | ```
604 |
605 | The most basic difference is that overloading is being done in the same class while for overriding base and child classes are required. Overriding is all about giving a specific implementation to the inherited method of parent class.
606 |
607 | Static binding is being used for overloaded methods and dynamic binding is being used for overridden/overriding methods.
608 | Performance: Overloading gives better performance compared to overriding. The reason is that the binding of overridden methods is being done at runtime.
609 |
610 | Private and final methods can be overloaded but they cannot be overridden. It means a class can have more than one private/final methods of same name but a child class cannot override the private/final methods of their base class.
611 |
612 | Return type of method does not matter in case of method overloading, it can be same or different. However in case of method overriding the overriding method can have more specific return type (meaning if, for example, base method returns an instance of Number class, all overriding methods can return any class that is extended from Number, but not a class that is higher in the hierarchy, like, for example, Object is in this particular case).
613 |
614 | Argument list should be different while doing method overloading. Argument list should be same in method Overriding.
615 | It is also a good practice to annotate overridden methods with `@Override` to make the compiler be able to notify you if child is, indeed, overriding parent's class method during compile-time.
616 |
617 | * **What are the access modifiers you know? What does each one do?**
618 | - There are four access modifiers in Java language (from strictest to the most lenient):
619 | 1. `private` *variables*, *methods*, *constructors* or *inner classes* are only visible to its' containing class and its' methods. This modifier is most commonly used, for example, to allow variable access only through getters and setters or to hide underlying implementation of classes that should not be used by user and therefore maintain encapsulation. Singleton constructor is also marked `private` to avoid unwanted instantiation from outside.
620 | 2. `Default` (no keyword is used) this modifier can be applied to *classes*, *variables*, *constructors* and *methods* and allows access from classes and methods inside the same package.
621 | 3. `protected` can be used on *variables*, *methods* and *constructors* therefore allowing access only to subclasses and classes that are inside the same package as protected members' class.
622 | 4. `public` modifier is widely-used on *classes*, *variables*, *constructors* and *methods* to grant access from any class and method anywhere. It should not be used everywhere as it implies that data marked with `public` is not sensitive and can not be used to harm the program.
623 |
624 | * **Can an Interface implement another Interface?**
625 | - Yes, an interface can implement another interface (and more than one), but it needs to use `extends`, rather than `implements` keyword. And while you can not remove methods from parent interface, you can add new ones freely to your sub-interface.
626 |
627 | * **What is Polymorphism? What about Inheritance?**
628 | - Polymorphism in Java has two types: Compile time polymorphism (static binding) and Runtime polymorphism (dynamic binding). Method overloading is an example of static polymorphism, while method overriding is an example of dynamic polymorphism.
629 |
630 | An important example of polymorphism is how a parent class refers to a child class object. In fact, any object that satisfies more than one IS-A relationship is polymorphic in nature.
631 |
632 | For instance, let’s consider a class `Animal` and let `Cat` be a subclass of `Animal`. So, any cat IS animal. Here, Cat satisfies the IS-A relationship for its own type as well as its super class Animal.
633 | - Inheritance can be defined as the process where one class acquires the properties (methods and fields) of another. With the use of inheritance the information is made manageable in a hierarchical order.
634 |
635 | The class which inherits the properties of other is known as subclass (derived class, child class) and the class whose properties are inherited is known as superclass (base class, parent class).
636 |
637 | Inheritance uses the keyword `extends` to inherit the properties of a class. Following is the syntax of extends keyword.
638 | ```java
639 | class Super {
640 | .....
641 | .....
642 | }
643 | class Sub extends Super {
644 | .....
645 | .....
646 | }
647 | ```
648 |
649 | * **Multiple inheritance in Classes and Interfaces in java** [Learn from here](http://codeinventions.blogspot.in/2014/07/can-interface-extend-multiple.html)
650 |
651 | * **What are the design patterns?** [Learn from here](https://blog.mindorks.com/mastering-design-patterns-in-android-with-kotlin)
652 | - Creational patterns
653 | - Builder [Wikipedia](https://en.wikipedia.org/wiki/Builder_pattern?oldformat=true)
654 | - Factory [Wikipedia](https://en.wikipedia.org/wiki/Factory_method_pattern?oldformat=true)
655 | - Singleton [Wikipedia](https://en.wikipedia.org/wiki/Singleton_pattern)
656 | - Monostate [Wikipedia](http://wiki.c2.com/?MonostatePattern)
657 | - Fluent Interface Pattern [Wikipedia](https://martinfowler.com/bliki/FluentInterface.html)
658 | - Structural patterns
659 | - Adapter [Wikipedia](https://en.wikipedia.org/wiki/Adapter_pattern?oldformat=true)
660 | - Decorator [Wikipedia](https://en.wikipedia.org/wiki/Decorator_pattern?oldformat=true)
661 | - Facade [Wikipedia](https://en.wikipedia.org/wiki/Facade_pattern?oldformat=true)
662 | - Behavioural patterns
663 | - Chain of responsibility [Wikipedia](https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern?oldformat=true)
664 | - Iterator [Wikipedia](https://en.wikipedia.org/wiki/Iterator_pattern?oldformat=true)
665 | - Strategy [Wikipedia](https://en.wikipedia.org/wiki/Strategy_pattern?oldformat=true)
666 |
667 | #### Collections and Generics
668 |
669 | * **Arrays Vs ArrayLists** - [Learn from here](https://stackoverflow.com/questions/32020000/what-is-the-difference-between-an-array-arraylist-and-a-list/32020072) and [here](https://www.youtube.com/watch?v=SMtSW3Zke_k)
670 |
671 | * **HashSet Vs TreeSet** - [Learn from here](https://stackoverflow.com/questions/25602382/java-hashset-vs-treeset-when-should-i-use-over-other)
672 |
673 | * **HashMap Vs Set** - [Learn from here](https://stackoverflow.com/questions/2773824/difference-between-hashset-and-hashmap)
674 |
675 | * **Stack Vs Queue** - [Learn from here](https://afteracademy.com/tech-interview/ds-algo-concepts/stack-and-queue)
676 |
677 | * **Explain Generics in Java?**
678 | - Generics were included in Java language to provide stronger type checks, by allowing the programmer to define, which classes can be used with other classes
679 | > In a nutshell, generics enable types (classes and interfaces) to be parameters when defining classes, interfaces and methods. Much like the more familiar formal parameters used in method declarations, type parameters provide a way for you to re-use the same code with different inputs. The difference is that the inputs to formal parameters are values, while the inputs to type parameters are types. ([Official Java Documentation](https://docs.oracle.com/javase/tutorial/java/generics/why.html))
680 |
681 | - This means that, for example, you can define:
682 | ```java
683 | List list = new ArrayList<>();
684 | ```
685 | And let the compiler take care of noticing, if you put some object, of type other than `Integer` into this list and warn you.
686 | - It should be noted that standard class hierarchy *does not* apply to generic types. It means that `Integer` in `List` is not inherited from `` - it is actually inherited directly from `
559 |