Optional parameters are an attribute of a method or delegate parameter. When you call a signature (method or delegate) that has a known optional parameter at compile-time, the compiler will insert the optional parameter value at the callsite. The runtime is not aware of optional parameters, so you can’t make a delegate that inserts an … Read more
It means that this method can receive more than one Object as a parameter. To better understating check the following example from here: The ellipsis (…) identifies a variable number of arguments, and is demonstrated in the following summation method. static int sum (int … numbers) { int total = 0; for (int i = … Read more
subjective 🙂 but honestly, I’d go with the Information Expert Pattern and say something like library.lend(item, patron) The library contains the information about the items it has (perhaps in its catalog). The library lends the item to the patron (which it knows because it registers them) Not sure how your instructor sees this, but this … Read more
Your question is answered by Mads Torgersen in the blog post you linked to: Actually interfaces are still quite far from abstract classes. Classes don’t inherit members from interfaces, so if a class leaves a member M implemented by the interface, the class does not have a member M! It’s like an explicit implementation today; … Read more
In Python2, you write class C(P): def __init__(self, a, b, c): super(C, self).__init__(a, b) self.c = c where the first argument to super is the child class and the second argument is the instance of the object which you want to have a reference to as an instance of its parent class. In Python 3, … Read more
A Design Pattern is a tried and tested solution to a common programming problem. It doesn’t necessarily have to be an Object Oriented programming problem, but that is most common these days. Learning to program is not hard for many people. It’s like playing with Legos: there’s a handful of different pieces you get to … Read more
It will be initialized by its default constructor. If you want to use a different constructor, you might have something like this: class Foo { public: Foo(int val) { } //stuff }; class Bar { public: Bar() : foo(2) { } Foo foo; };
In most cases when I’ve had to have two things reference each other, I’ve created an interface to remove the circular reference. For example: BEFORE public class Foo { Bar myBar; } public class Bar { Foo myFoo; } Dependency graph: Foo Bar ^ ^ | | Bar Foo Foo depends on Bar, but Bar … Read more
There is absolutely no way to do this in Java; it would break the language specification. JLS 12 Execution / 12.5 Creation of New Class Instances Just before a reference to the newly created object is returned as the result, the indicated constructor is processed to initialize the new object using the following procedure: Assign … Read more
Make ShowBike.Bicycle static. public class ShowBike { private static class Bicycle { public int gear = 0; public Bicycle(int v) { gear = v; } } public static void main() { Bicycle bike = new Bicycle(5); System.out.println(bike.gear); } } In Java there are two types of nested classes: “Static nested class” and “Inner class”. Without … Read more