# What is the value of s? ``` NSMutableString *s = [NSMutableString stringWithString: @"123"]; [s appendString: @"456"]; ``` - [x] 123456 - [ ] 123 - [ ] 456 - [ ] This code contains an error. # What's the value of i after these statements? ``` NSString *str = nil; NSInteger i = str.integerValue; ``` - [ ] nil - [x] 0 (technically `nil` == 0 but i will have a literal value of `0` and not the `void*` value of `nil`) - [ ] -1 - [ ] This code crashes. # What value is in str after this line in executed? `NSString str = "test" + " " + "more";` - [x] This code contains an error - [ ] test - [ ] nil - [ ] test more # What does this code print? ``` NSPredicate *p2 = [NSPredicate predicateWithBlock:^BOOL(NSString* evaluatedObject, NSDictionary * _Nullable bindings) { return evaluatedObject.intValue % 2 == 0; }]; NSArray *vals = @[@"1", @"2", @"3"]; NSArray *n2 = [vals filteredArrayUsingPredicate:p2]; NSLog(@"%@", n2.firstObject); ``` - [x] 2 - [ ] 1,2,3 - [ ] 1,2 - [ ] Nothing, since this code contains an error. # Property defaults include \_? - [x] atomic/strong - [ ] atomic/weak - [ ] nonatomic/weak - [ ] nonatomic/strong # What is the key difference between NSDictionary and NSMutableDictionary? - [x] NSMutableDictionary's values can change - [ ] NSMutableDictionary has not initializers. - [ ] NSDictionary can't be copied. - [ ] NSDictionary's values can change. # What is foo? `-(float)foo;` - [x] A function with a return type of float. - [ ] This code contains an error. - [ ] A variable declaration of type float. - [ ] A property of type float. # What can you glean from this line? `#import "NSString+NameHelper.h"` - [x] NameHelper is a category of NSString. - [ ] NameHelper is a subclass of NSString. - [ ] NSString implements the NameHelper protocol. - [ ] NSString has a helper class. # What's wrong with this code? `float x = 5.;` - [x] 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. # How many times with this loop be executed? ``` for (int x=0; x<100; x++) { x = x + 1; } ``` - [x] 50 - [ ] 99 - [ ] 100 - [ ] This code contains an error. # What is this code an example of? `[self addObserver: self forKeyPath: @"val" options:0 context: nil];` - [x] Key-Value Observing - [ ] Class Value Observing - [ ] Key-Data Observing - [ ] KeyPath Observing # What does ARC stand for? - [x] Automatic Reference Counting - [ ] Automatic Retain Checking - [ ] Async Retain Cycles - [ ] Automatic Release Code # What is printed for this code? ``` int val = 0; val = 1.5; printf("%d", val); ``` - [x] 1 - [ ] 2 - [ ] 0 - [ ] This code contains an error. # What best describes class inheritance in Objective-C? - [x] single inheritance but multiple protocol implementation - [ ] Objective-C doesn't support inheritance - [ ] dual class inheritance - [ ] unlimited class inheritance and protocol adherence # How many keys does this NSDictionary have after this code is executed? `NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys: @"b", @"e", @"a", @"r", nil];` - [x] 2 - [ ] 4 - [ ] 5 - [ ] This code contains an error. # What is wrong with this code? ``` NSMutableDictionary *dict1 = [NSMutableDictionary dictionaryWithCapacity:5]; [dict1 setValue:@"key" forKey:@"value"]; ``` - [ ] The key and value items are mixed - [x] Nothing is wrong with it - [ ] You can't set the capacity of a dictionary - [ ] NSMutableDictionary doesn't have a :setValue:forKey function. # What is printed from this code? ``` NSData *data = [@"print" dataUsingEncoding:NSASCIIStringEncoding]; NSLog(@"%@", [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding]); ``` - [x] print - [ ] This code is invalid - [ ] Nothing is printed from this code. - [ ] nil # What is different about this function? `+(void)doSomething;` - [x] It is static - [ ] It is abstract. - [ ] It is inline. - [ ] This code contains an error. # Structs can have \_? - [ ] functions - [ ] initializers - [x] fields - [ ] all of these answers # What is wrong with this code? ``` @interface MyClass : NSObject @property (strong, nonatomic, readonly) NSString *name; @end ``` - [x] There is nothing wrong with this code. - [ ] There is not read-only directive. - [ ] MyClass doesn't implement NSObject. - [ ] Properties are declared in the implementation. # What is an enums base type for the code below? `typedef enum { Foo1, Foo2} Foo;` - [x] There is no base type. - [ ] NSObject - [ ] int - [ ] NSNumber # If you want to store a small amount of information (e.g., user settings), whats the best, built-in way to go? - [x] UserDefaults - [ ] plist file - [ ] CoreData - [ ] TextFile # What are categories used for? - [x] to extend other classes - [ ] to manage access control - [ ] to coordinate objects - [ ] to group classes # What is this Objective-C code checking? ``` if ([keyPath isInstanceOf:[NSString class]]) { } ``` - [x] 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 # What is this a declaration of? `int(^foo)(int);` - [ ] an Extension - [ ] a Generic - [x] a block of code - [ ] an abstract class # 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; ``` - [x] 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. # 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. - [x] Nothing is wrong with this code. # What's the difference between an array and a set? - [x] Arrays are ordered, non-unique values. - [ ] Arrays are stored sorted. - [ ] Sets are ordered, unique values. - [ ] Sets can contain nils. # Dot notation can be used for \_? - [ ] nothing, as they're never used in Objective-C - [ ] function calls only - [x] property getter/setter - [ ] parameter delimiters # 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]; ``` - [x] 2,3 - [ ] nil - [ ] This code contains an error - [ ] 2,"3" # 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]; - [x] [self foo:5 b:10]; # 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 # 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 - [x] The parameter is passed by reference and may be changed # What is printed from this code execution? ``` typedef enum { thing1, thing2, thing3 } Thing; -(void) enumStuff { NSLog(@"%d", thing2); } ``` - [ ] 0 - [x] 1 - [ ] thing2 - [ ] This code does not print anything # 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 - [x] atomic # 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. - [x] Nothing is wrong with it. # What is special about the code within this block? ``` dispatch_async(dispatch_get_main_queue(), ^{ // code }); ``` - [x] 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. # 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 - [x] five # What is wrong with this code? ``` NSDictionary *d1 = @[@"v1", @4, @"v2", @5.6, @"v3"]; NSlog(@"d1: %@", d1); ``` - [ ] NSDictionary cannot be printed this way. - [x] The last key is missing a value. - [ ] Dictionaries cannot have mixed types as values. - [ ] d1 is assigned an NSArray of values. # What is the initial value of the property `val`? ``` @property (nonatomic, readonly) int val; ``` - [ ] 8 - [ ] nil - [ ] -1 - [ ] undefined