Uninstantiated class variable in Java subclass

This question already has an answer here: What's wrong with overridable method calls in constructors? 7 answers I have the following code: The constructor of class A calls an abstract method implemented by class B which returns a variable from class

Construct Haskell data types with many fields

I have data type data Constants = Constants { x1 :: Int, x2 :: Int, ... , x100 :: Int } Names x1, x2, ..., x100 may have irregular naming. Is there an elegant way to create Constants object from list of 100 Int values? mkConstants :: [Int] -> Constan

Detect the type of parameter passed in the class constructor

I want the constructor of a class to be able to pass two types of parameters, then inside the method do some stuff based on the type of the parameter. the types would be double and String[]. the class and its constructor is something similar to: publ

Why is my Promise definition executed?

I am quite new with Promises and want to know why is it that my Promise definition gets executed without me calling a .then() or resolve on it. var promise = new Promise(function (resolve, reject) { console.log("Starting loader"); resolve(); });

Java constructor of an abstract class

As far as I know (please correct me if I'm wrong) a class that is abstract cannot be instantiated. You can give it a constructor, but just can't call new on that class. If you call super in a subclass, the superclass constructor will run (and thus cr

to call a C ++ parent constructor

Is there any advantage to calling the parent constructor explicitly in the derived class constructor? is this: LockableDoor :: LockableDoor() : Door(), locked_(true) { } is different from this: LockableDoor :: LockableDoor() : locked_(true) { } someh

Is it ok to initialize the constructor of an activity?

I am curious about what can I do in the constructor of an activity. Is it ok to do the initialization in the constructor? Thanks.Do initialization in Activity's constructor is bad approach also you cant initialize views in constructor. Better way to

Inheritance Builder Call Result

There are two classes. One inherited from the other one. Test results surprise me since I called the child class constructor and its method. However I do not call the super class constructor like this new Cougar().go();. But output shows the the supe

Get initialization of the base class constructor, a bad habit?

I have a base class in an OpenGL project which represents 3DModel in general. Now I want to create a more specialized class that will inherits from 3DModel. My problem is the mandatory base class constructor call in the initialization list. Is there

What are the problems with writing like this?

I had a conversation with a friend of mine about object assignment and construction the other day, and he made a point that assignment a = b for objects is (semantically) equivalent to destroying a and then re-constructing it from b (at the same plac

Call the constructor on a double board via Streams

I am wondering if the following is possible with Java 8, for: Patch[][] patches = new Patch[width][depth]; I want to call the constructor using Streams, I know there is Arrays.stream(patches) which would give me a Stream<Patch[]>, so unfortunately I

Build an object with many private collection fields

What is the most efficient and clean way to create an object of a class that has like 10 private fields that are collections (eg. HashMap, LinkedHashMap, ArrayList etc). If I put a constructor with 10 fields in it it would look like nightmare.You can

Create an instance using the base constructor

For reasons out of the scope of the question, I'm needing to dynamically create an instance of a child class that inherits from a base class, calling a constructor that doesn't exist with an argument passed to the base class constructor Using example

Formatting the constructor of the class f #

I am creating a program that takes an email and converts it into json. In the interest of learning functional languages I thought it would be a good opportunity to learn F#. So first off I want a message class that can then easily be serialized into

How to properly connect classes (stack overflow in builders)

I'm relatively new to Java and I'm coding extensions/plugins for online game Minecraft. I've recently started "bigger" projects which require more classes to preserve neatness. I am still trying to fully understand how constructors work, but mos

Constructors for structures that do nothing

Edit: Just to be clear, the struct doesn't do anything, as in it has no functions. I think I gave the impression that I thought using an initialiser list and leaving the body of the constructor empty was the issue at hand. Say I'm using a struct to h

Do the constructor arguments get GC'ed?

I am using a system which needs to initialize many objects using transactions, and for reasons beyond the scope of this question these transactions must be passed into the constructors. Like this: trait Mutable class Txn(i: Int) { def newID(implicit

C ++ methods override in python

suppose a C++ class has several constructors which are overloaded according the number and type and sequences of their respective parameters, for example, constructor(int x, int y) and constructor(float x, float y, float z), I think these two are ove

Object instance without new?

As we know we can instantiate an object without new keyword by using classloader/object cloning/object serialization. When I am using these techniques to create an object, is the constructor called or not?For Object.clone no constructor is called. Fo

Why do not builders return values?

Please tell me why the constructor does not return any value. I want a perfect technical reason to explain to my students why the constructor does not have any return type.What actually happens with the constructor is that the runtime uses type data