Your classpath is broken (which is a very common problem in the Java world). Depending on how you start your application, you need to revise the argument to -cp, your Class-Path entry in MANIFEST.MF or your disk layout.
If you want two classes on one element, do it this way: Reference it in css like so: Example:
The differences between a class and a struct in C++ is: struct members and base classes/structs are public by default. class members and base classes/struts are private by default. Both classes and structs can have a mixture of public, protected and private members, can use inheritance and can have member functions. I would recommend you: … Read more
It’s a pointer, so instead try: Basically the operator . (used to access an object’s fields and methods) is used on objects and references, so: If you have a pointer type, you have to dereference it first to obtain a reference: The a->b notation is usually just a shorthand for (*a).b. A note on smart … Read more
Use the abc module to create abstract classes. Use the abstractmethod decorator to declare a method abstract, and declare a class abstract using one of three ways, depending upon your Python version. In Python 3.4 and above, you can inherit from ABC. In earlier versions of Python, you need to specify your class’s metaclass as ABCMeta. Specifying the metaclass has different … Read more
Data classes are just regular classes that are geared towards storing state, rather than containing a lot of logic. Every time you create a class that mostly consists of attributes, you make a data class. What the dataclasses module does is to make it easier to create data classes. It takes care of a lot … Read more
The java <class-name> command syntax First of all, you need to understand the correct way to launch a program using the java (or javaw) command. The normal syntax1 is this: where <option> is a command line option (starting with a “-” character), <class-name> is a fully qualified Java class name, and <arg> is an arbitrary command line argument that gets passed to your application. 1 – There … Read more
The java <class-name> command syntax First of all, you need to understand the correct way to launch a program using the java (or javaw) command. The normal syntax1 is this: where <option> is a command line option (starting with a “-” character), <class-name> is a fully qualified Java class name, and <arg> is an arbitrary … Read more
super() lets you avoid referring to the base class explicitly, which can be nice. But the main advantage comes with multiple inheritance, where all sorts of fun stuff can happen. See the standard docs on super if you haven’t already. Note that the syntax changed in Python 3.0: you can just say super().__init__() instead of super(ChildB, self).__init__() which IMO is quite a bit nicer. The … Read more
The reason you need to use self. is because Python does not use the @ syntax to refer to instance attributes. Python decided to do methods in a way that makes the instance to which the method belongs be passed automatically, but not received automatically: the first parameter of methods is the instance the method is called on. That makes methods entirely the … Read more