abstract

问题 This question already has an answer here: What's wrong with overridable method calls in constructors? 7 answers Let\'s suppose I have an abstract Base class that implements Runnable interface. public abstract class Base implements Runnable { protected int param; public Base(final int param) { System.out.println(\"Base constructor\"); this.param = param; // I\'m using this param here new Thread(this).start(); System.out.println(\"Derivative thread created with param \" + param); } @Override

问题 C# methods in interfaces are declared without using the virtual keyword, and overridden in the derived class without using the override keyword. Is there a reason for this? I assume that it is just a language convenience, and obviously the CLR knows how to handle this under the covers (methods are not virtual by default), but are there other technical reasons? Here is the IL that a derived class generates: class Example : IDisposable { public void Dispose() { } } .method public hidebysig

问题 Recently I started exploring Java 8 and I can\'t quite understand the concept of \"functional interface\" that is essential to Java\'s implementation of lambda expressions. There is a pretty comprehensive guide to lambda functions in Java, but I got stuck on the chapter that gives definition to the concept of functional interfaces. The definition reads: More precisely, a functional interface is defined as any interface that has exactly one abstract method. An then he proceeds to examples, one

问题 How can I make a class or method abstract in Python? I tried redefining __new__() like so: class F: def __new__(cls): raise Exception(\"Unable to create an instance of abstract class %s\" %cls) but now if I create a class G that inherits from F like so: class G(F): pass then I can\'t instantiate G either, since it calls its super class\'s __new__ method. Is there a better way to define an abstract class? 回答1: Use the abc module to create abstract classes. Use the abstractmethod decorator to

问题 Consider an example (which compiles in java) public abstract interface Interface { public void interfacing(); public abstract boolean interfacing(boolean really); } Why is it necessary for an interface to be \"declared\" abstract? Is there other rules that applies with an abstract interface? Finally: If abstract is obsolete, why is it included in Java? Is there a history for abstract interface? 回答1: Why is it necessary for an interface to be "declared" abstract? It's not. public abstract