superclass

问题 Hi I'm wondering if there is a simple solution to my problem, I have an ArrayList : ArrayList <Animal> animalList = new ArrayList<Animal>(); /* I add some objects from subclasses of Animal */ animalList.add(new Reptile()); animalList.add(new Bird()); animalList.add(new Amphibian()); They all implement a method move() - The Bird flies when move() is called. I know I can access common methods and properties of the super class by using this public void feed(Integer animalIndex) { Animal aAnimal

问题 Okay, so, for example, let's say I have an abstract class called "Vehicle". The Vehicle class, has, among other things, a static variable called wheels, which is not initialized. What I want to do is have other subclasses extending from the Vehicle class, like "Motorcycle", and "Truck", and in these subclasses, have the wheels initialized. Code: public abstract class Vehicle { static int wheels; //number of wheels on the vehicle } But the below doesn't work: public class Motorcycle extends

问题 This question already has answers here : What is the difference between public, protected, package-private and private in Java? (28 answers) Closed 2 years ago . It seems very silly, but I am really confused. Please see below code: package com.one; public class SuperClass { protected void fun() { System.out.println("base fun"); } } ---- package com.two; import com.one.SuperClass; public class SubClass extends SuperClass{ public void foo() { SuperClass s = new SuperClass(); s.fun(); // Error

问题 I was told that for a Java subclass it can inherit all members of its superclass. So does this mean even private members? I know it can inherit protected members. Can someone explain this to me. I am now totally confused. 回答1: No, the private member are not inherited because the scope of a private member is only limited to the class in which it is defined. Only the public and protected member are inherited. From the Java Documentation, Private Members in a Superclass A subclass does not

问题 I tried to do some operation ( setParent ) on an object in Python (an instance of a class which inherits from a different class - to be specific, QtGui.QLabel ), but during runtime the above error was raised. The object itself has had some fields with actual content (verified on debug), but from some reason I couldn't "use" it. What does the error mean and how can I fix it? For some additional information, I shall say that the object was returned from a static method before I tried to do this

问题 I tried to do some operation ( setParent ) on an object in Python (an instance of a class which inherits from a different class - to be specific, QtGui.QLabel ), but during runtime the above error was raised. The object itself has had some fields with actual content (verified on debug), but from some reason I couldn't "use" it. What does the error mean and how can I fix it? For some additional information, I shall say that the object was returned from a static method before I tried to do this

问题 I'm dealing with a class which extends JFrame . It's not my code and it makes a call to super before it begins constructing the GUI. I'm wondering why this is done since I've always just accessed the methods of the superclass without having to call super(); 回答1: There is an implicit call to super() with no arguments for all classes that have a parent - which is every user defined class in Java - so calling it explicitly is usually not required. However, you may use the call to super() with

问题 How can I access state variable of class KeyBoardPlayer with an object of class KalaPlayer ? /** * An abstract class representing a player in Kala. Extend this class * to make your own players (e.g. human players entering moves at the keyboard * or computer players with programmed strategies for making moves). */ public abstract class KalaPlayer { /** * Method by which a player selects a move. * @param gs The current game state * @return A side pit number in the range 1-6 * @throws

问题 I've got an issue creating entities in Kotlin. In particular, it's about passing data to a super class. Find an example below. I've got an abstract super class called Trackable that classes can extend. It has a user property that stores who has created that particular object. abstract class Trackable( var createdBy: User ) : Persistable() An class called Contract would now implement the Trackable super class with a compile-time error for the time being: @Entity data class Contract( var

问题 I just started learning this, so sorry if this has some obvious solution I still can't grasp. I have these two classes: @implementation Person -(void)saySomething:(NSString*) something { NSLog(@"%@",something); } -(void)yellSomething:(NSString*) something { [self saySomething:[something uppercaseString]]; } @end and @implementation ShoutingPerson : Person -(void)saySomething:(NSString*)something { [super yellSomething:something]; } @end This is causing a circular reference call because