Mobile OS Interview Questions
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Swift defines the AnyObject type alias to represent instances of any reference type, and it’s internally defined as a protocol. Consider the following code: var array = [AnyObject]() struct Test {} array.append(Test()) This code generates a compilation error, with the following error message: Type 'Test' does not conform to protocol 'AnyObject' The failure is obvious because a struct is a value and not a reference type, and as such it doesn’t implement and cannot be cast to the AnyObject protocol. Now consider the following code: var array = [AnyObject]() array.append(1) array.append(2.0) array.append("3") array.append([4, 5, 6]) array.append([7: "7", 8: "8"]) struct Test {} array.append(Test()) The array array is filled in with values of type respectively int, double, string, array and dictionary. All of them are value types and not reference types, and in all cases no error is reported by the compiler. Why?

1 1131

Consider the following code: let op1: Int = 1 let op2: UInt = 2 let op3: Double = 3.34 var result = op1 + op2 + op3 Where is the error and why? How can it be fixed?

1 1217

Consider the following code: var defaults = NSUserDefaults.standardUserDefaults() var userPref = defaults.stringForKey("userPref")! printString(userPref) func printString(string: String) { println(string) } Where is the bug? What does this bug cause? What’s the proper way to fix it?

1 1234




The following code snippet results in a compile time error: struct IntStack { var items = [Int]() func add(x: Int) { items.append(x) // Compile time error here. } } Explain why a compile time error occurs. How can you fix it?

1 1268

In Swift enumerations, what’s the difference between raw values and associated values?

1 2585

The String struct doesn’t provide a count or length property or method to count the number of characters it contains. Instead a global countElements() function is available. When applied to strings, what’s the complexity of the countElements function: O(1) O(n) and why?

1 975

struct Planet { var name: String var distanceFromSun: Double } let planets = [ Planet(name: "Mercury", distanceFromSun: 0.387), Planet(name: "Venus", distanceFromSun: 0.722), Planet(name: "Earth", distanceFromSun: 1.0), Planet(name: "Mars", distanceFromSun: 1.52), Planet(name: "Jupiter", distanceFromSun: 5.20), Planet(name: "Saturn", distanceFromSun: 9.58), Planet(name: "Uranus", distanceFromSun: 19.2), Planet(name: "Neptune", distanceFromSun: 30.1) ] let result1 = planets.map { $0.name } let result2 = planets.reduce(0) { $0 + $1.distanceFromSun } What are the types and values of the result1 and result2 variables? Explain why.

1 1081

Consider the following code: var array1 = [1, 2, 3, 4, 5] var array2 = array1 array2.append(6) var len = array1.count What’s the value of the len variable, and why?

1 1093

what is the procedure of using D2MS server in cloud messaging in android

Tech Mentro,

559

what is preferences

Tech Mentro, Google,

552

sap bw online classes

SAP Labs,

1 347







Un-Answered Questions { Mobile OS }

what is the difference between nonatomic & atomic ? which is thread safe and why

485


In mapKit frame work, how to get current user location

490


Difference between iOS 3 , iOS4, iOS 5, iOS 6, iOS 7 and iOS 8 (What are the new features)

573


If the Activity is showing an animation that indicates some kind of progress, what issue might you encounter and how could you address it?

583


Explain @synchronized ,@dynamic

695






Mention what is the difference between Swift and ‘Objective-C’ language?

470


What does Ubuntu mean?

448


What’s Canonical’s role in OpenStack? 

425


How to get the geolocation data on a picture?

440


Explain application states

343


What is the correct way to check if a Compass sensor is present on the system? Explain your answer.

775


How you can use built-in Messaging within your application?

409


When dealing with property declarations, what is the difference between atomic and non-atomic?

495


DB updation when app new version comes ?

320


Explain what is the stack of autorelease pools. How autorelease pool work under the hood?

434