static members belong to the class instead of a specific instance. It means that only one instance of a static field exists[1] even if you create a million instances of the class or you don’t create any. It will be shared by all instances. Since static methods also do not belong to a specific instance, … Read more
Like most of the other answers have said, instance methods use an instance of a class, whereas a class method can be used with just the class name. In Objective-C they are defined thusly: @interface MyClass : NSObject + (void)aClassMethod; – (void)anInstanceMethod; @end They could then be used like so: [MyClass aClassMethod]; MyClass *object = … Read more
Assuming you are asking why you can’t do this: public interface IFoo { void Bar(); } public class Foo: IFoo { public static void Bar() {} } This doesn’t make sense to me, semantically. Methods specified on an interface should be there to specify the contract for interacting with an object. Static methods do not … Read more
You should use @Override whenever possible. It prevents simple mistakes from being made. Example: class C { @Override public boolean equals(SomeClass obj){ // code … } } This doesn’t compile because it doesn’t properly override public boolean equals(Object obj). The same will go for methods that implement an interface (1.6 and above only) or override … Read more
With ECMAScript5’s Function.prototype.bind things get pretty clean: function newCall(Cls) { return new (Function.prototype.bind.apply(Cls, arguments)); // or even // return new (Cls.bind.apply(Cls, arguments)); // if you know that Cls.bind has not been overwritten } It can be used as follows: var s = newCall(Something, a, b, c); or even directly: var s = new (Function.prototype.bind.call(Something, null, … Read more
You forget the tricky 2nd difference between classes and structs. Quoth the standard (ยง11.2.2 in C++98 through C++11): In absence of an access-specifier for a base class, public is assumed when the derived class is declared struct and private is assumed when the class is declared class. And just for completeness’ sake, the more widely … Read more
I wrote an article about that: Abstract classes and interfaces Summarizing: When we talk about abstract classes we are defining characteristics of an object type; specifying what an object is. When we talk about an interface and define capabilities that we promise to provide, we are talking about establishing a contract about what the object … Read more
For two objects, Foo and Bar the relationships can be defined Association – I have a relationship with an object. Foo uses Bar public class Foo { private Bar bar; }; NB: See Fowler’s definition – the key is that Bar is semantically related to Foo rather than just a dependency (like an int or … Read more
Using these magic methods (__enter__, __exit__) allows you to implement objects which can be used easily with the with statement. The idea is that it makes it easy to build code which needs some ‘cleandown’ code executed (think of it as a try-finally block). Some more explanation here. A useful example could be a database … Read more
Yes, the first function has no relationship with an object instance of that constructor function, you can consider it like a ‘static method’. In JavaScript functions are first-class objects, that means you can treat them just like any object, in this case, you are only adding a property to the function object. The second function, … Read more