objective-c-quiz.md

Objective-C

Q1. What is the value of s?

NSMutableString *s = [NSMutableString stringWithString: @"123"];
[s appendString: @"456"];

• 123456
• 123
• 456
• This code contains an error.

Q2. What's the value of i after these statements?

NSString *str = nil;
NSInteger i = str.integerValue;

• nil
• 0 (technically nil == 0 but i will have a literal value of 0 and not the void* value of nil)
• -1
• This code crashes.

Q3. What value is in str after this line in executed?

NSString str = "test" + " " + "more";

• This code contains an error
• test
• nil
• test more

Q4. What does this code print?

    NSPredicate *p2 = [NSPredicate predicateWithBlock:^BOOL(NSString*  evaluatedObject, NSDictionary<NSString *,id> * _Nullable bindings) {
      return evaluatedObject.intValue % 2 == 0;
    }];
    NSArray *vals = @[@"1", @"2", @"3"];
    NSArray *n2 = [vals filteredArrayUsingPredicate:p2];
    NSLog(@"%@", n2.firstObject);

• 2
• 1,2,3
• 1,2
• Nothing, since this code contains an error.

Q5. Property defaults include _?

• atomic/strong
• atomic/weak
• nonatomic/weak
• nonatomic/strong

Q6. What is the key difference between NSDictionary and NSMutableDictionary?

• NSMutableDictionary's values can change
• NSMutableDictionary has not initializers.
• NSDictionary can't be copied.
• NSDictionary's values can change.

Q7. What is foo?

-(float)foo;

• A function with a return type of float.
• This code contains an error.
• A variable declaration of type float.
• A property of type float.

Q8. What can you glean from this line?

#import "NSString+NameHelper.h"

• NameHelper is a category of NSString.
• NameHelper is a subclass of NSString.
• NSString implements the NameHelper protocol.
• NSString has a helper class.

Q9. What's wrong with this code?

float x = 5.;

• Nothing is wrong with this code.
• Declarations do not need semicolons.
• x=5 is an invalid float.
• Variables can't be declared and initialized in the same state.

Q10. How many times with this loop be executed?

for (int x=0; x<100; x++) {
  x = x + 1;
}

• 50
• 99
• 100
• This code contains an error.

Q11. What is this code an example of?

[self addObserver: self forKeyPath: @"val" options:0 context: nil];

• Key-Value Observing
• Class Value Observing
• Key-Data Observing
• KeyPath Observing

Q12. What does ARC stand for?

• Automatic Reference Counting
• Automatic Retain Checking
• Async Retain Cycles
• Automatic Release Code

Q13. What is printed for this code?

int val = 0;
val = 1.5;
printf("%d", val);

• 1
• 2
• 0
• This code contains an error.

Q14. What best describes class inheritance in Objective-C?

• single inheritance but multiple protocol implementation
• Objective-C doesn't support inheritance
• dual class inheritance
• unlimited class inheritance and protocol adherence

Q15. How many keys does this NSDictionary have after this code is executed?

NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys: @"b", @"e", @"a", @"r", nil];

• 2
• 4
• 5
• This code contains an error.

Q16. What is wrong with this code?

NSMutableDictionary *dict1 = [NSMutableDictionary dictionaryWithCapacity:5];
[dict1 setValue:@"key" forKey:@"value"];

• The key and value items are mixed
• Nothing is wrong with it
• You can't set the capacity of a dictionary
• NSMutableDictionary doesn't have a :setValue:forKey function.

Q17. What is printed from this code?

NSData *data = [@"print" dataUsingEncoding:NSASCIIStringEncoding];
NSLog(@"%@", [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding]);

• print
• This code is invalid
• Nothing is printed from this code.
• nil

Q18. What is different about this function?

+(void)doSomething;

• It is static
• It is abstract.
• It is inline.
• This code contains an error.

Q19. Structs can have _?

• functions
• initializers
• fields
• all of these answers

Q20. What is wrong with this code?

@interface MyClass : NSObject
    @property (strong, nonatomic, readonly) NSString *name;
  @end

• There is nothing wrong with this code.
• There is not read-only directive.
• MyClass doesn't implement NSObject.
• Properties are declared in the implementation.

Q21. What is an enums base type for the code below?

typedef enum { Foo1, Foo2} Foo;

• There is no base type.
• NSObject
• int
• NSNumber

Q22. If you want to store a small amount of information (e.g., user settings), whats the best, built-in way to go?

• UserDefaults
• plist file
• CoreData
• TextFile

Q23. What are categories used for?

• to extend other classes
• to manage access control
• to coordinate objects
• to group classes

Q24. What is this Objective-C code checking?

if ([keyPath isInstanceOf:[NSString class]]) {
}

• This code contains an error
• if keyPath is an instance of NSString
• if keyPath's baseclass is the same as NSString's baseclass
• if keyPath implements the same methods as NSString

Q25. What is this a declaration of?

int(^foo)(int);

• an Extension
• a Generic
• a block of code
• an abstract class

Q26. For observing changes to a property, which of these two statements cause the related method to be called and why?

1. _val = 1;
2. self.val= 100;

• Statement 2, since it calls the auto-created setter on the property.
• Statement 1, since it uses the property directly.
• Statement 2, since it specifies the class instance to use.
• Statement 1, since it calls the auto-created setter on the property.

Q27. What is wrong with this code?

float x = 2.0;
int(^foo)(int) = ^(int n1) {
  return (int)(n1*x);
};
foo(5);

• Ints and floats can't be multiplied.
• The parameter isn't declared correctly.
• x is not in the right scope.
• Nothing is wrong with this code.

Q28. What's the difference between an array and a set?

• Arrays are ordered, non-unique values.
• Arrays are stored sorted.
• Sets are ordered, unique values.
• Sets can contain nils.

Q29. Dot notation can be used for _?

• nothing, as they're never used in Objective-C
• function calls only
• property getter/setter
• parameter delimiters

Q30. What is the value of newVals after this code is executed?

    NSArray *vals = @[@"1", @"2", @"3"];
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF.intValue > 1"];
    NSArray *newVals = [vals filteredArrayUsingPredicate:pred];

• 2,3
• nil
• This code contains an error
• 2,"3"

Q31. How would this function be called?

-(int)foo:(int)a b:(int)c;

• self.foo(5, b:10);
• This code contains an error.
• [self foo:5:10:20];
• [self foo:5 b:10];

Q32. What is the type of the error return value stored in json?

    NSError *error;
    NSData *data;
    id json = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];

• NSString
• NSArray
• id
• NSDictionary

Q33. What is significant about this function declaration?

    -(void)testFunc:(NSString**)str;

• The parameter is passed by value and can not be changed
• ** is not allowed on a parameter
• The parameter may be nil
• The parameter is passed by reference and may be changed

Q34. What is printed from this code execution?

    typedef enum {
        thing1,
        thing2,
        thing3
    } Thing;


    -(void) enumStuff {
        NSLog(@"%d", thing2);
    }

• 0
• 1
• thing2
• This code does not print anything

Q35. You are worried about threaded access to a property and possible collision in writing. What directive should you use on the property?

• non-atomic
• strong
• weak
• atomic

Q36. What is wrong with this line of code?

int temp = 1==1;

• temp is a keyword.
• 1==1 is invalid.
• 1==1 evaluates to a Boolean.
• Nothing is wrong with it.

Q37. What is special about the code within this block?

dispatch_async(dispatch_get_main_queue(), ^{
// code
});

• It executes on the main queue.
• It is the last code to run before the app goes inactive.
• It executes on a background thread.
• It is queued to execute in the background.

Q38. How many items are in set1 after this code executes?

NSMutableSet *set1 = [NSMutableSet setWithObjects: @1,@2, @3, @4, @5, nil];
[set1 add0bject:@3];

• zero
• six
• one
• five

Q39. What is wrong with this code?

NSDictionary *d1 = @[@"v1", @4, @"v2", @5.6, @"v3"];
NSlog(@"d1: %@", d1);

• NSDictionary cannot be printed this way.
• The last key is missing a value.
• Dictionaries cannot have mixed types as values.
• d1 is assigned an NSArray of values.

Q40. What is the initial value of the property val?

@property (nonatomic, readonly) int val;

• 8
• nil
• -1
• undefined

Q41. Which thread should UI updates be processed on to avoid crashes and application lag?

• UI
• dispatch
• background
• main