implements

How to force implementation of a method in subclass without using abstract?

由 余生长醉 提交于 2019-12-03 23:10:39
I want to force subclass to implement an implemented method of my mother class. I look this Java - Force implementation of an implemented method but i can't convert my mother class to an abstract class. public class myMotherClass { myMethod { ...some code .. } } public class myClass extends myMotherClass { myMethod { ... other code ... } } So, in this exemple, I want to force myClass implement myMethod. Sorry for my english... You can not force a subclass to override a method. You can only force it to implement a method by making it abstract. So if you can not make myMotherClass abstract you

implementing Comparable interface from abstract class with concrete subclasses

由 ℡╲_俬逩灬. 提交于 2019-12-03 21:09:27
package geometricobject; public abstract class GeometricObject implements Comparable { private String color = "white"; private boolean filled; private java.util.Date dateCreated; protected GeometricObject(){ dateCreated = new java.util.Date(); } protected GeometricObject(String color, boolean filled){ dateCreated = new java.util.Date(); this.color = color; this.filled = filled; } public String getColor(){ return color; } public void setColor(String color){ this.color = color; } public boolean isFilled(){ return filled; } public void setFilled(boolean filled){ this.filled = filled; } public

Check if a generic T implements an interface

由 ≡放荡痞女 提交于 2019-12-03 16:29:52
问题 so I have this class in Java: public class Foo<T>{ } and inside this class I want to know if T implements certain interface. The following code DOES NOT work but it's the idea of what I want to accomplish: if(T.class implements SomeInterface){ // do stuff } so I want to check if the class T that was passed to Foo have implements SomeInterface on its signature. Is it possible? How? 回答1: Generics, oddly enough, use extends for interfaces as well. 1 You'll want to use: public class Foo<T extends

Implement an interface and override methods in Java?

由 大兔子大兔子 提交于 2019-12-02 14:55:13
问题 Why do you have to override all methods of an interface? For instance if I have public class Foo extend JFrame implements ActionListener, KeyListener { foo(){ } @Override public void keyPressed(KeyEvent arg) { } @Override public void keyReleased(KeyEvent arg) { } @Override public void keyTyped(KeyEvent arg) { } } I'm going to have lots of methods I won't even be using, is there a way to remove the un used implemented methods, for instance if i plan to use one method from the interface I don't

Cyclic inheritance and interfaces - class A can't implement class B interface while class B implements A interface

由 巧了我就是萌 提交于 2019-11-30 08:43:17
问题 I have: public class A implements BListener { public interface AListener {} } public class B implements AListener { public interface BListener {} } So, if I understand correctly the cyclic inheritance happens because: The compiler goes to A and says "hey, A implements BListener, let's go find BListener!" Then when it tries to find BListener, it eventually gets to B , which it says: "Hey, BListener, needed for A is inside B! BUT WAIT! B needs AListener! Let's go find AListener!" And then it

Interface extends another interface but implements its methods

由 烈酒焚心 提交于 2019-11-29 20:45:58
In java when an interface extends another interface: Why does it implement its methods? How can it implement its methods when an interface can't contain a method body How can it implement the methods when it extends the other interface and not implement it? What is the purpose of an interface implementing another interface? This has major concepts in Java! EDIT: public interface FiresDragEvents { void addDragHandler(DragHandler handler); void removeDragHandler(DragHandler handler); } public interface DragController extends FiresDragEvents { void addDragHandler(DragHandler handler); void

java.lang.Number doesn't implement “+” or any other operators?

由 自闭症网瘾萝莉.ら 提交于 2019-11-29 10:21:01
I'm creating a class which is supposed to be able to be used with an array of any type of number (float, int, etc), so here is one method I have: // T extends Number public synchronized T[] average() { Number[] ret = new Number[queue[0].length]; for (int i = 0; i < ret.length; ++i) { for (int j = 0; j < size; ++j) { ret[i] += queue[j][i]; // WTF ERROR?! } ret[i] /= size; // WTF ERROR?! } return (T[])ret; } Except this won't compile because "Number" doesn't implement the "+=" or "/=" operators. Event worse, java's Number class doesn't implement even the most basic operators like "+" or "-"! How

implements vs extends in generics in Java

由 一世执手 提交于 2019-11-29 07:26:08
问题 Can someone tell me what the differences between the first and second codes are? MaxPQ stands for priority queue, which is a collection of "Key" objects that can be compared with each other. Code 1: public class MaxPQ<Key extends Comparable<Key>>{ ... } Code 2: public class MaxPQ<Key implements Comparable<Key>>{ ... } The second code doesn't compile, but it is not intuitive to me why we need to extend instead of implement interfaces when using a generic. 回答1: The difference is pretty

Cyclic inheritance and interfaces - class A can't implement class B interface while class B implements A interface

由 有些话、适合烂在心里 提交于 2019-11-29 07:22:13
I have: public class A implements BListener { public interface AListener {} } public class B implements AListener { public interface BListener {} } So, if I understand correctly the cyclic inheritance happens because: The compiler goes to A and says "hey, A implements BListener, let's go find BListener!" Then when it tries to find BListener, it eventually gets to B , which it says: "Hey, BListener, needed for A is inside B! BUT WAIT! B needs AListener! Let's go find AListener!" And then it gets to A, repeat. Did I get this right? By the way, this compilation error happened to me on Android

Why “extends” precedes “implements” in class declaration [closed]

由 删除回忆录丶 提交于 2019-11-28 16:30:58
Why must implement always be written after extend in a class declaration? For example: public class Register extends ActionSupport implements ModelDriven Why can it not be: public class Register implements ModelDriven extends ActionSupport The latter produces a compile-time error. When the Java compiler turns a class into bytecode, it must first look to a parent class. That is because the underlying implementation of classes is to point to the bytecode of the parent class - which holds the relevant methods and fields. Then it adds in pointers to the code of the child class functions - some of
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