UpWork (oDesk) & Elance Objective-C Test Question & Answers

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Ques : Which of the following is the fastest?
Ans  : Mutex implicit locking

Ques : How do you free an object?
Ans  :  [obj release]

Ques :  What is the isa variable in objects?
Ans  : Object class identification

Ques : What is true regarding C functions inside .m files?
Ans  : They can contain Obj-C code

Ques : What does the following imply?

Worker *ceo = [[Worker alloc] init];
ceo->boss = nil;
Ans  : That the boss instance variable is declared @public

Ques : Can you send messages to nil?
Ans  : Yes

Ques :  In which version of Objective-C did the fast enumeration system appear?
Ans  : 2.0

Ques : What comments are supported in Obj-C?
Ans  :  // Line comments

Ques : What type of variable do you need to use to implement singletons?
Ans  : static

Ques : As categories can't have instance variables, what class could you use to implement a full class only with categories?
Ans  :  NSMutableDictionary

Ques : How do you throw an exception?
Ans  : @throw exception

Ques : What is true regarding strings?
Ans  : Obj-C strings are not of static storage

Ques : How do you include the root "Object" class?
Ans  : It depends on the compiler

Ques : What is true regarding @protected?
Ans  : The instance variable is accessible within the class that declares it and within classes that inherit it

Ques : What is a protocol?
Ans  :  An interface without an implementation

Ques :  Which of the following is incorrect?
Ans  : [AClass release]

Ques : How do you allocate an object?
Ans  : MyClass *obj = [MyClass alloc];

Ques : What will be the output of the following code?

static int
a (void)
{
printf ("a\n");
return 0;
}

static int
b (void)
{
printf ("b\n");
return 1;
}

static int
c (void)
{
printf ("c\n");
return 2;
}

int
main (int argc, const char *argv[])
{
printf ("%d %d %d", a (), b (), c ());
return 0;
}
Ans  : a b c 0 1 2

Ques : What is nil?
Ans  : The null object

Ques : Can an exception caught in @catch be re-thrown?
Ans  : Yes

Ques : What class specifiers are supported?
Ans  : There is no such thing as class specifiers

Ques : Which of the following declares a protocol?
Ans  : @protocol ProtocolName

Ques : What is the Obj-C runtime?
Ans  : A C library

Ques : What's the difference between copy and deepCopy?
Ans  : copy creates a copy at the first level, while deepCopy copies the instance variables

Ques : Which of the following can be inherited?
Ans  : Protocols

Ques : A method can be tagged to be called only by a specific class and its subclasses.
Ans  : False

Ques : Which of the following is not recommended?
Ans  : None of the above

Ques : A class can have two methods with the same name, but with different argument types.
Ans  : False

Ques : What are @try and @catch?
Ans  :  Exception keywords

Ques : A class can conform to only one protocol.
Ans  : False

Ques : Which of the following creates a class that conforms to a protocol?
Ans  : @interface ClassName

Ques : What is the id type?
Ans  :  A generic C type that Objective-C uses for an arbitrary object

Ques : What is a @finally block?
Ans  :  A block of code that is run whenever an exception is thrown or not

Ques : Is the following code a correct allocation?

MyClass myObj;
[&myObj aMessage];
Ans  : No

Ques : What is not supported in Obj-C?
Ans  : Method argument default value

Ques : Which of the following does not happen when you throw an exception in a @synchronized block?
Ans  : The object is deallocated

Ques : What can be linked to an Obj-C program without any particular process?
Ans  : C libraries

Ques : What is the C type used to work with objects in Obj-C?
Ans  : pointer

Ques : What is a category?
Ans  :  A category is a way to add methods to a class which already exists

Ques : Protocols are like classes; they can inherit.
Ans  : True

Ques : Which of the following is false?
Ans  : When a method is called, the send is automatically available as the sender variable, like self or super

Ques : What happens if two categories define methods with the same names for the same class?
Ans  :  At runtime, either method will be called

Ques : What can you do with categories?
Ans  : Add methods to a class without subclassing it

Ques : In which version of Objective-C did the properties system appear?
Ans  :  2.0

Ques : What is the default visibility for instance variables?
Ans  : @protected

Ques : What happens if you release an unretained object twice?
Ans  : MemoryException is raised

Ques : In Obj-C 2.0, what do the fast enumeration protocols rely on to provide fast Enumerations?
Ans  :  C arrays

Ques : What can you use to avoid the msgSend function overhead?
Ans  : SEL

Ques : Which C feature is not supported in Obj-C?
Ans  :  Support is compiler dependant

Ques : What does Obj-C not support?
Ans  : Automatic variables

Ques : When using the garbage collector, which method, that is normally called without the collector, is not called on your objects where they are collected?
Ans  : dealloc

Ques : What can be used as Object instance variables?
Ans  : pointers

Ques : What is a SEL?
Ans  : A pointer to a method

Ques : What is an IMP?
Ans  : The C type of a method implementation pointer

Ques : What is true regarding @public?
Ans  : It breaks encapsulation

Ques : What is an autoreleased object?
Ans  : An object that will be released when the current AutoreleasePool is deallocated.

Ques : If you need to allocate custom memory, in which method will you do so?
Ans  : None of the above

Ques : What is #import
Ans  :  C preprocessor construct to avoid multiple inclusions of the same file

Ques : What is true regarding messaging?
Ans  :  Messaging is fully dynamic, which means you can compile some code that sends a message to a class that doesn't implement it, and add a category later, in a dynamic library for example

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