extends | 易学教程

How to extend a class with a member of its own type?

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问题 Suppose we need to implement different types of tree with a class called "BaseNode" from which other type of Nodes are derived and it suppose to have an instance variable called parent of its own type, generally it looks like: class BaseNode{ //...some fields BaseNode parent; //...other methods } Now if I am going to derive Node for AVL tree with more members: class AVLNode extends BaseNode{ //...other useful stuff } the original parent (& left & right )node members will still be type

How to find the overridden method in Eclipse?

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问题 When I am looking at a method in eclipse java, how do I jump to the method it overrides/extends? 回答1: Three ways to go about it. Hyperlink Method (Mouse + Keyboard) Press CTRL while hovering over the overriden method. You should see an option called 'Open Super Implementation. Click it ! From here : Keyboard shortcut And for bonus points, you can setup a Keyboard shortcut to do this like so : When you try to setup a keyboard shortcut, you may filter by typing Open Super Im . On my Eclipse

Issue with declaration of Map<String,Class<? extends Serializable>>

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Java provides me by <? extends class> a way of filtering the java classes that you can use to build in this case the new HashMap, for example: I can do that: Map<String,? extends Serializable> map1 = new HashMap<String,String>(); It is correct, because String implements Serializable, so the compiler let me do that. But when i try to do it: Map<String,GenericClass<? extends Serializable>> map2 = new HashMap<String, GenericClass<String>>(); Being the GenericClass as it: public class GenericClass<T> { . . . } The compiler throw an error saying: Type mismatch: cannot convert from HashMap<String

Difference for <? super/extends String> in method and variable declaration

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问题 Given: import java.util.*; public class Hancock { //insert code here list.add("foo"); } } Which two code fragments, inserted independently at line 5, will compile without warnings? (Choose two) A. public void addString(List list) { B. public void addString(List<String> list) { C. public void addString(List<? super String> list) { D. public void addString(List<? extends String> list) { Correct answers are B & C. Answers A and B are quite clear for me. For the answers C & D i know which way the

Is List<Double> a subtype of List<? extends Number> and why?

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问题 Here is what I know: Double is a subtype of Number and List<Double> is not a subtype of List<Number> . List<Dog> is not a subtype of List<Animal> because you can add Cat to List<Animal> but you can't do that with List<Dog> . List<? extends Number> means this list can store variables of type Number and variables of subtype of Number. List<Double> means this list can store variables of type Double. Please correct me if anything above is wrong and then Is List<Double> a subtype of List<? extends

Extending Protobuf Messages

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I have many different schemas, however there are a set of fields which every schema contains. I was wondering if there was a way to have a different schema extend a parent schema and inherit its fields. For example this is what I want: message Parent { required string common1 = 0; optional string common2 = 1; } message Child1 { // can we extend the Parent? // I want common1, common2 to be fields here required int c1 = 2; required string c2 = 3; } message Child2 { // can we extend Parent? // I want common1, common2 to be fields here repeated int c3 = 2; repeated string c4 = 3; } Such that

How do I call a super constructor in Dart?

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问题 How do I call a super constructor in Dart? Is it possible to call named super constructors? 回答1: Yes, it is, the syntax is close to C#, here is an example with both default constructor and named constructor: class Foo { Foo(int a, int b) { //Code of constructor } Foo.named(int c, int d) { //Code of named constructor } } class Bar extends Foo { Bar(int a, int b) : super(a, b); } class Baz extends Foo { Baz(int c, int d) : super.named(c, d); } If you want to initialize instance variables in the

Java Inner Class extends Outer Class

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There are some cases in Java where an inner class extends an outer class. For example, java.awt.geom.Arc2D.Float is an inner class of java.awt.geom.Arc2D, and also extends Arc2D. (c.f. http://download.oracle.com/javase/6/docs/api/java/awt/geom/Arc2D.Float.html ) Also, sun.org.mozilla.javascript.internal.FunctionNode.Jump extends sun.org.mozilla.javascript.internal.Node, which is a superclass of FunctionNode. (sorry... cannot find a link to the javadoc) To me, this seems odd. Could you then create these? new Arc2D.Float.Float() //n.b. I couldn't get this to compile in Intellij IDEA; new

Extending Array in Actionscript 3 (Flex)

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I'm trying to make a variation on Array for a very specific purpose. When I have the following: public class TileArray extends Array { // Intentionally empty - I get the error regardless } Why can't I do this? var tl:TileArray = [1,2,3]; despite the fact that I can do this var ar:Array = [1,2,3]; The error I receive is this: Implicit coercion of a value with static type Array to a possibly unrelated type Instead of extending Array you could write your own class that exposes all the methods of Array. By employing the Proxy class you can redirect all default Array methods to an internal array

How to create a base view in backbone.js?

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问题 I need to create a base view which all my views would extends. I'm not really sure where and when to declare this view. Basically, I need to inject global variables to all my templates and I don't do to that in each and every render() methods. this is my tree structure for now: |-main.js |-app.js |-require.js |-App | |-View | | |-Dashboard.js | | |-Header.js | | |-Content.js | |-Model | |-Collection | |-Template | |-Libs |-... this is my app.js var App = { ApiURL: "http://domain.local", View: