Tech Interview

Front 1

What are the 4 Pillars of OOP?

Back 1

Inheritance, Encapsulation, Abstraction, and Polymorphism

Front 2

What is Encapsulation?

Back 2

Grouping of variables and methods within a class to define how an object will behave when it is created. For example

public class Animal {

int age;

String gender;

// Required Parameters to create Animal

// object

public Animal (int age, String gender) {

this.age = age;

this.gender = gender;

}

// method can be used with created Animal

// object

public void eat() {

System.out.println("Eating...");

}

}

// Main class to create Animal objects

public class Zoo {

public static void main(String[] args) {

// Animal object creation with parameters

Animal cat = new Animal (4, "Kitty");

// Method from Animal class

cat.eat();

}

}

Front 3

What is Abstraction?

Back 3

Allows for a class to both declare and define methods to be used as a Parent class when creating children. •public class Jaime extends Abstract• Undefined methods from the Abstract Class must be defined and implemented in child class. •public void eat() {System.out.println("Lactose free foods")}•

Front 4

What is Polymorphism?

Back 4

A method used by different classes that has the same name but different definitions. For example move() can be used by a car, human, and animal class but defined for each class differently. A car can drive, a human can walk, and an animal can swim but they all move()

Front 5

What is Inheritance?

Back 5

Allows for an class to use methods from another class to create objects with those borrowed methods. For example, Jaime class can borrow move() from Human class and move() can be defined in the Jaime class. Jaime must extend from Human to borrow those methods. •public class Jaime extends Human{}•

Front 6

What is OOP?

Back 6

Object Oriented Programming. Instead of having all the code in one file, split the code into multiple files to be more organized.

Front 7

What is an Android Studio Service?

Back 7

An event that runs in the background not without needing to interact with the user and it works even if the app is destroyed. For example, a music player playing music even when the user leaves the app.

Front 8

What is the Activity Lifecycle?

Back 8

onCreate, onStart, onPause, onResume, onStop, onDestroy

Front 9

What is an Interface?

Back 9

A class that declares methods to be used and defined by another class. For example, if multiple classes will be using getData() an interface with that method can be created to clean up the code from redundant code.

Front 10

What is SQLite?

Back 10

A local Database emedded in the app that a user gets data from.

Front 11

What is a Cursor?

Back 11

Used to send data from a database using ContentProvider to give it's data to another app.

Front 12

What is CRUD?

Back 12

Create, read, update, and delete in SQLite

Front 13

What is JSON Parsing?

Back 13

The collection and reading of data whether it is stored data locally or done so with pulling data from the web.

Front 14

What is Espresso?

Back 14

Part of Test Driven development. @Test used to test specific functions like a button to make sure it is working properly within an Activity.

Front 15

What is the difference between Interface and Abstract Class?

Back 15

Interface allows you to declare a method whereas abstract classes allow you to declare a method and define a method

Front 16

What is SDLC?

Back 16

System development life cycle. Analysis (what we don't want), planning (what we do want), design(how will we get what we want), build, test (did we get what we want), deploy (let's use what we got), and maintenance (let's get close to what we want).

Front 17

What is MVP?

Back 17

Model View Presenter. A way to organize code focused on Test Driven Development.

Front 18

What are Android Architecture Components?

Back 18

Room, ViewModel, LiveData, RecyclerView. UI lifecycle and data persistence. Make sure things load easier, prevent memory leaks.

Front 19

What is MVVM?

Back 19

Model View ViewModel. A way to organize code with a focus on Databases, event based. View updates ViewModel of users actions, ViewModel sends relevant data to the View, DataModel extracts the data from the source to give to the ViewModel.

Front 20

What is REST?

Back 20

Representational State Transfer. A way to access web services/data. JSON and XML can be used.

Front 21

What is SOAP?

Back 21

Simple Object Access Point. A way to access web services/data. HTTP and XML exclusive.

Front 22

What is MVC?

Back 22

Model View Controller. Controller gets the data, sends it to the model, tells the view to get the data from the model.

Front 23

What is RxJava?

Back 23

Simplifies thread executions. For example simplifies AsyncTasks.

Front 24

What is the difference between SOAP and REST?

Back 24

REST is more flexible allowing the use of HTTP, JSON, XML, and URL. SOAP is exclusive with HTTP and XML.

Front 25

What is MySQL?

Back 25

An outside web based server database that a user gets data from using a network connection.

Front 26

What is the difference between SQLite and MySQL?

Back 26

SQLite is a database embedded in the app that a user gets data from. MySQL is an web based server database that the user gets data from.

Front 27

What is a Broadcast?

Back 27

A system or app event occurs like when a file is downloaded, airplane mode is on or off.

Front 28

What is a BroadcastReceiver?

Back 28

Allows you to subscribe to a system or app event to be notified when it happens in the app.

Front 29

What is a Content Provider?

Back 29

Allows for one app to gain access to another apps database using Content Resolver (asker) and Cursor (giver).

Front 30

What is a Content Resolver?

Back 30

Used to request data from another apps database.

Front 31

What is an Android App?

Back 31

Essentially an android app consists of Activities (programs that the user interacts with), services (programs that run in the background or provide some function to other apps), and broadcast receivers (programs that catch information important to your app).

Front 32

Activity life cycle - Can I save all my database updates in onStop()?

Back 32

No. onPause. In case of low memory or configuration changes, onStop might not be called.

Front 33

What is the difference between this and getapplicationcontext?

Back 33

This is tied to the current activity lifecycle and getapplicationcontext is tied to the whole app lifecycle.

Front 34

What is the UI response time limit in android?

Back 34

5 seconds in general and 10 seconds for a BroadcastReceiver.

Front 35

What is Bundle? How it is different from parcel?

Back 35

A bundle is used for sending simple intent data to another activity. Parcel is used for more complex methods to send to another activity.

Front 36

How to write a custom adapter?

Back 36

Create layout for adapter view, Class with data setters/getters, create those data objects main activity and add data objects to ArrayList, create custom adapter Class to override getview and pass in objects from ArrayList.

Front 37

How to fix an android application crash? How to analyze a crash using logcat?

Back 37

Analyze the logcat by looking for the blue links. Above the blue links will be the main crash error. The blue links lead to where the crash occurred. If no blue links, use search for "error" or "fail".

Front 38

What is a singleton class?

Back 38

What is a singleton class?Object created only one time and will not be destroyed until the app process is destroyed. Used globally.

Front 39

How to save UI states in case of configuration changes? (eg: screen orientation changes).

Back 39

Create String key variables. Override onSaveInstanceState and pass in data to string key variables. Call onSaveInstanceState in onCreate to pass string key variables to views like TextView.

Front 40

What is a fragment? How it differs from activity?

Back 40

Fragment is part of an activity with it's own UI and lifecycle. Activity exists independently while Fragment exists within an activity.

Front 41

How to parse JSON data that is coming from a server?

Back 41

Create a class with AsyncTask that fetches the data from the URL. Create and iterate JSONArray to create JSONObject that goes through the JSON data.

Front 42

What is 9 patch image? when to use it?

Back 42

A resizable PNG image with custom parameters that can be used for displaying text within the image.

Front 43

How will you write an application which fits both for mobiles and tablets?

Back 43

Create a separate layout with smallestWidth at 600dp and adjust the layout.

Front 44

What is the Memory limit of each process in android?

Back 44

Varies from device but generally 16mb is the given memory for each device.

Front 45

What kernel is used in android?

Back 45

Monolithic Kernal. Linux based.

Front 46

How to fetch a contact person number from contact application using content provider?

Back 46

Must use a Content Resolver (asker) to connect to the content provider and a Cursor (giver) to send that data.

Front 47

How to upgrade data base tables in the later versions of an application?

Back 47

Under onCreate use onUpgrade to the current version number. Make sure in onCreate table is being created.

Front 48

What is the difference between dynamic receiver and static receiver? when will you use dynamic broadcast receivers?

Back 48

Static is when app is not running and dynamic is only when app is running. Dynamic can be used when we only want music to play when app is open for example to save battery life.

Front 49

What is intent, pending intent, and sticky intent?

Back 49

Intent communicates actions immediately in Android. PendingIntent is an intent that will occur at a later time, alarm clock going off. Sticky Intent will keep getting updates on a service like battery life.

Front 50

What is the difference between thread and a service?

Back 50

Service runs on the main UI thread and thread runs on its own separate thread.

Front 51

How will you create an async task?

Back 51

Create class that extends AsyncTask and override doInBackground. Then run the desired methods. onPostExecute to update UI.

Front 52

What is a handler thread? how it is different from normal thread?

Back 52

Handler communicates with and handles multiple threads to send to the message que to update the UI. Thread by itself executes outside the message que and can't update the UI.

Front 53

What is looper, handler, and message queue?

Back 53

Looper cycles through the threads sent from the handler in a message queue that stores the threads to be performed and update the UI.

Front 54

How to update UI from another thread?

Back 54

Use AsyncTask onPostExecute. Once thread process is done onPostExecute updates UI.

Front 55

How to pass data between 2 components of android?

Back 55

Send the data using a new Intent.putextra and create a bundle to get the data on the other end.

Front 56

What is a binder service? how it differs from started service?

Back 56

Binder service establishes a connection between something and is destroyed when calling component is destroyed. Started keeps running. BinderService to track user but stops when app closes. Started service with music player to keep playing music after app closes.

Front 57

If I write a background functionality in an activity, should I use a thread or service?

Back 57

A service and extend it with AsyncTask to safely run it in the background.

Front 58

What is ANR? What is the cause of ANR and how will you rectify this problem?

Back 58

Application not responding. Usually caused by long running actions main thread. Using AsyncTasks helps to run long tasks in the background safely.

Front 59

How to do inter-thread communication in android, using handlers?

Back 59

Use a Handler thread which already creates a message que. Add a handler to communicate with the Looper and the MainThreadUi.

Front 60

How to create a service with single thread?

Back 60

Create a service class that extends AsyncTask.

Front 61

Why android uses DVM, why not JVM?

Back 61

More efficient with low memory usage and better performance running multiple instances. Auto garbage collector.

Front 62

How will you display database tables in an activity? will you use gridview or tableview? justify?

Back 62

I would use a GridView with a RecyclerView. If data gets large, GridView will allow for scrolling and better performance and UI design.

Front 63

What is the difference between abstract class and an interface?

Back 63

Abstract class has methods that are both declared and defined. Interface Only declared methods.

Front 64

Can you give some real time example where you have used an interface and abstract class?

Back 64

For a Movie App, I used an interface integrated with an AsyncTask abstract class to populate the MainActivity UI with a list of movies from The Movies Database API.

Front 65

How will achieve multiple inheritance using interfaces?

Back 65

Create one public Interface with multiple interfaces.

Front 66

What are all the collection framework classes you have used in your application?

Back 66

Essentially an android app consists of Activities (programs that the user interacts with), services (programs that run in the background or provide some function to other apps), and broadcast receivers (programs that catch information important to your app).

Front 67

What is the difference between ArrayList and Vector? which one is better?

Back 67

Vector is synchronized and ArrayList is not. ArrayList has better performance.

Front 68

What is the difference between Hashtable and hashmap?

Back 68

Hashtable is synchronized and hashmap isn't. Hashmap can have null key and any number of null values. ConcurrentHashMap makes it thread safe.

Front 69

What is the difference between JVM, JRE, and JDK?

Back 69

Java Virtual Machine emulates the Java code. Java Runtime Environment provides all needed files to run JVM. Java Development Kit is what compiles, documents, and packages Java programs.

Front 70

How does RxJava work?

Back 70

Observables (emit data) and Observers (catch the data onNext(), catch errors onError(), catch completion onCompleted())

Front 71

RxJava: Difference between onJust and onCallable?

Back 71

onJust interacts with local data like a String List. onCallable interacts with network calls like online movie list. 1) Create new thread subscribeOn(), 2) update data to main thread observeOn(), 3) connect to observable list with subscribe(),

Front 72

What's the difference between Observable and Single?

Back 72

Single uses onSingleSubscriber and uses onSuccess() and onError().

Front 73

Difference between Picasso and Glide?

Back 73

Glide is more customizable, uses less memory, and allows for GIF support. Picasso loads from url faster, Glide loads faster from cache.

Front 74

What is Dagger 2?

Back 74

Dependency Injection; consolidating dependencies in a configuration class.

Front 75

Difference between OpenAPI and Swagger?

Back 75

OpenAPI = specification and Swagger = tools for implementing an API with the specification.

Front 76

How many Intents are there?

Back 76

3; explicit (intent resolved by specific application) and implicit (intent resolved by multiple applications) and broadcast intent (intent sent out to anyone who cares to listen like another app).

Front 77

Difference between Implicit and Explicit intent?

Back 77

Implicit Intent is resolved by multiple applications and Explicit is resolved by a specific app.