? as a type parameter can only be used in methods. eg: printAll(MyList<? extends Serializable>) I cannot define classes with ? as type parameter. A wildcard (?) isn’t a formal type parameter, but rather can be used as a type argument. In the example you give, ? extends Serializable is given as a type argument …
That is how Java works. The constructors of the parent classes are called, all the way up the class hierarchy through Object, before the child class’s constructor is called. Quoting from the docs: With super(), the superclass no-argument constructor is called. With super(parameter list), the superclass constructor with a matching parameter list is called. Note: …
Your idea to have a variable of type Animal is good. But you also have to make sure to use the right constructor: Animal animal; // define a variable for whatever animal we will create if (condition) { Dog dog = new Dog(); // create a new Dog using the Dog constructor dog.setD(..); dog.setE(..); animal …
For single inheritance, super() is just a fancier way to refer to the base type. That way, you make the code more maintainable, for example in case you want to change the base type’s name. When you are using super everywhere, you just need to change it in the class line. The real benefit comes …
Because it will ensure that when a constructor is invoked, it can rely on all the fields in its superclass being initialised. see 3.4.4 in here
Are you reloading modules somehow in the middle of things? If so, that may explain this error. isinstance(self,DBAdminConnection) may become false after reloading modules because of the changes to memory references, apparently. Edit: if you’re running your web.py app under mod_wsgi, make sure you’re disabling autoreload: app = web.application(urls, globals(), autoreload=False)
You can register a custom Jackson annotation intropector which would ignore all the properties that come from the certain super type. Here is an example: public class JacksonIgnoreInherited { public static class Base { public final String field1; public Base(final String field1) { this.field1 = field1; } } public static class Bean extends Base { …
Constructors are not inherited, you must create a new, identically prototyped constructor in the subclass that maps to its matching constructor in the superclass. Here is an example of how this works: class Foo { Foo(String str) { } } class Bar extends Foo { Bar(String str) { // Here I am explicitly calling the …
Use an interface if you want to define a contract. I.e. X must take Y and return Z. It doesn’t care how the code is doing that. A class can implement multiple interfaces. Use an abstract class if you want to define default behaviour in non-abstract methods so that the endusers can reuse it without …
Use Reflection from the Type of the current class. Type superClass = myClass.GetType().BaseType;