The designated initializer is the one that all the other initializers must call. UIView and subclasses are a little unusual in that they’ve actually got two such initializers: -initWithFrame: and -initWithCoder:, depending on how the view is created. You should override -initWithFrame: if you’re instantiating the view in code, and -initWithCoder: if you’re loading it … Read more
Just assign to the instance variable directly, without using dot syntax to call the setter: – (void) setProp1:(id)aProp { self->prop1 = aProp; } That kind of begs the question though. All this accessor does is exactly what the parent would have done – so what’s the point of overriding the parent at all?
? as a type parameter can only be used in methods. eg: printAll(MyList<? extends Serializable>) I cannot define classes with ? as type parameter. A wildcard (?) isn’t a formal type parameter, but rather can be used as a type argument. In the example you give, ? extends Serializable is given as a type argument … Read more
Your idea to have a variable of type Animal is good. But you also have to make sure to use the right constructor: Animal animal; // define a variable for whatever animal we will create if (condition) { Dog dog = new Dog(); // create a new Dog using the Dog constructor dog.setD(..); dog.setE(..); animal … Read more
I’m not Swift ninja but I would write MyClass as: class MyClass: NSObject { var someProperty: NSString // no need (!). It will be initialised from controller init(fromString string: NSString) { self.someProperty = string super.init() // can actually be omitted in this example because will happen automatically. } convenience override init() { self.init(fromString:”John”) // calls … Read more
The solution I found was to create a new function in the subclass that has the same name as the inherited function. In this case push. Then inside the overriding function the inherited function is called via the super keyword. class newArray extends Array{ push(value) { //execute any logic require before pushing value onto array … Read more
Python’s scoping rules for barenames are very simple and straightforward: local namespace first, then (if any) outer functions in which the current one is nested, then globals, finally built-ins. That’s all that ever happens when a barename is looked up, and there’s no need to memorize or apply any complicated rules (nor is there any … Read more
Firstly, I recommend you follow Björn Pollex’s advice (+1). To get past this particular problem (type(l2 + l3) == CustomList), you need to implement a custom __add__(): def __add__(self, rhs): return CustomList(list.__add__(self, rhs)) And for extended slicing: def __getitem__(self, item): result = list.__getitem__(self, item) try: return CustomList(result) except TypeError: return result I also recommend… pydoc … Read more
In addition to Chuck’s answer, you also have to initialize your new introduced property before calling super.init A designated initializer must ensure that all of the properties introduced by its class are initialized before it delegates up to a superclass initializer. (The Swift Programming Language -> Language Guide -> Initialization) Thus, to make it work: … Read more
A subclass is a class that extends another class. public class BaseClass{ public String getFoo(){ return “foo”; } } public class SubClass extends BaseClass{ } Then… System.out.println(new SubClass().getFoo()); Will print: foo This works because a subclass inherits the functionality of the class it extends.