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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