No, the constructor of the parent class is not called if the child class defines a constructor. From the constructor of your child class, you have to call the constructor of the parent’s class : parent::__construct(); Passing it parameters, if needed. Generally, you’ll do so at the beginning of the constructor of the child class, … Read more
Making the __init__ an abstract method: from abc import ABCMeta, abstractmethod class A(object): __metaclass__ = ABCMeta @abstractmethod def __init__(self, n): self.n = n if __name__ == ‘__main__’: a = A(3) helps: TypeError: Can’t instantiate abstract class A with abstract methods __init__ Python 3 version: from abc import ABCMeta, abstractmethod class A(object, metaclass=ABCMeta): @abstractmethod def __init__(self, … Read more
A constructor in Java doesn’t actually “build” the object, it is used to initialize fields. Imagine that your abstract class has fields x and y, and that you always want them to be initialized in a certain way, no matter what actual concrete subclass is eventually created. So you create a constructor and initialize these … Read more
Interfaces cannot have state associated with them. Abstract classes can have state associated with them. Furthermore, default methods in interfaces need not be implemented. So in this way, it will not break already existing code, as while the interface does receive an update, the implementing class does not need to implement it. As a result … Read more
It’s a little too verbose in my opinion, but works: public abstract class MyClass<T extends MyClass<T>> implements Comparable<T> { } public class SubClass extends MyClass<SubClass> { @Override public int compareTo(SubClass o) { // TODO Auto-generated method stub return 0; } }
The serialVersionUID is provided to determine compatibility between a deseralized object and the current version of the class. As such, it isn’t really necessary in the first version of a class, or in this case, in an abstract base class. You’ll never have an instance of that abstract class to serialize/deserialize, so it doesn’t need … Read more
I wouldn’t do either. Instead I would make it use the correct class in both cases. public abstract class AbstractFoo { protected final Log log = LogFactory.getLog(getClass()); … } public class Foo extends AbstractFoo { public void someMethod() { log.info(“Using abstract log”); } } If you are not doing lots of logging (which is a … Read more
Yes, you can do this by calling this.getClass(). This will give you the Class instance for the runtime type of this. If you just want the name of the class, you could use this.getClass().getName(). Lastly, there are also this.getClass().getSimpleName() and this.getClass().getCanonicalName(). I use the former all the time to print readable class names to log … Read more
I have that kind of spring setup working an abstract class with an autowired field public abstract class AbstractJobRoute extends RouteBuilder { @Autowired private GlobalSettingsService settingsService; and several children defined with @Component annotation.
Abstract classes are useful when you need a class for the purpose of inheritance and polymorphism, but it makes no sense to instantiate the class itself, only its subclasses. They are commonly used when you want to define a template for a group of subclasses that share some common implementation code, but you also want … Read more