A possibly a bit better solution compared to the accepted answer: from better_abc import ABCMeta, abstract_attribute # see below class AbstractFoo(metaclass=ABCMeta): @abstract_attribute def bar(self): pass class Foo(AbstractFoo): def __init__(self): self.bar = 3 class BadFoo(AbstractFoo): def __init__(self): pass It will behave like this: Foo() # ok BadFoo() # will raise: NotImplementedError: Can’t instantiate abstract class BadFoo … Read more
You have two options: 1. Use a Protocol Define the superclass as a Protocol instead of a Class Pro: Compile time check for if each “subclass” (not an actual subclass) implements the required method(s) Con: The “superclass” (protocol) cannot implement methods or properties 2. Assert in the super version of the method Example: class SuperClass … Read more
For the interface, the addition of the abstract, or even the public keywords would be redundant, so you omit them: interface MyInterface { void Method(); } In the CIL, the method is marked virtual and abstract. (Note that Java allows interface members to be declared public abstract). For the implementing class, there are some options: … Read more
You can do what you described by having a final field in your abstract class that is initialised in its constructor (untested code): abstract class Base { final String errMsg; Base(String msg) { errMsg = msg; } abstract String doSomething(); } class Sub extends Base { Sub() { super(“Sub message”); } String doSomething() { return … Read more
It’s a long, sad story. When PHP 5.2 first introduced this warning, late static bindings weren’t yet in the language. In case you’re not familiar with late static bindings, note that code like this doesn’t work the way you might expect: <?php abstract class ParentClass { static function foo() { echo “I’m gonna do bar()”; … Read more
Of course. Declaring a class abstract only means that you don’t allow it to be instantiated on its own. Declaring a method abstract means that subclasses have to provide an implementation for that method. The two are separate concepts, though obviously you can’t have an abstract method in a non-abstract class. You can even have … Read more
JavaScript Classes and Inheritance (ES6) According to ES6, you can use JavaScript classes and inheritance to accomplish what you need. JavaScript classes, introduced in ECMAScript 2015, are primarily syntactical sugar over JavaScript’s existing prototype-based inheritance. Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes First of all, we define our abstract class. This class can’t be instantiated, but can be extended. We … Read more
According to the Java Language Specification, the abstract keyword for interfaces is obsolete and should no longer be used. (Section 9.1.1.1) That said, with Java’s propensity for backwards compatibility, I really doubt it will ever make a difference whether the abstract keyword is present.
It’ll have abstract as one of its modifiers when you call getModifiers() on the class object. This link should help. Modifier.isAbstract( someClass.getModifiers() ); Also: http://java.sun.com/javase/6/docs/api/java/lang/reflect/Modifier.html http://java.sun.com/javase/6/docs/api/java/lang/Class.html#getModifiers()
Why is it necessary for an interface to be “declared” abstract? It’s not. public abstract interface Interface { \___.__/ | ‘—-> Neither this… public void interfacing(); public abstract boolean interfacing(boolean really); \___.__/ | ‘—-> nor this, are necessary. } Interfaces and their methods are implicitly abstract and adding that modifier makes no difference. Is there … Read more