overriding | 易学教程

What to return when overriding Object.GetHashCode() in classes with no immutable fields?

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问题 Ok, before you get all mad because there are hundreds of similar sounding questions posted on the internet, I can assure you that I have just spent the last few hours reading all of them and have not found the answer to my question. Background: Basically, one of my large scale applications had been suffering from a situation where some Binding s on the ListBox.SelectedItem property would stop working or the program would crash after an edit had been made to the currently selected item. I

TimePicker onTimeSet not being called

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I'm using a time picker to let the user enter his desired time to do a specific task, I'm using the DialogFragment class that's available in the support library for backward compatibility with older Android versions. Here is my code to create the TimePickerFragment class, created in a seperate file, taken from: http://developer.android.com/guide/topics/ui/controls/pickers.html : package com.calls.only; import java.util.Calendar; import android.app.Dialog; import android.app.TimePickerDialog; import android.os.Bundle; import android.support.v4.app.DialogFragment; import android.widget

Eclipse rename/refactoring override

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问题 I am new to eclipse plug-in development. I want to customize the renaming of a project. I need to validate the new name. So how can I override eclipse's rename/refactoring method? I saw something related to RenameParticipant, but didn't understand clearly. It would be great if someone could explain me steps to override the renaming functionality. Many Thanks, Ann 回答1: The rename refactoring has several processors that subclass org.eclipse.ltk.core.refactoring.participants.RenameProcessor and

scala generic method overriding

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问题 I have an abstract class : abstract class Foo(...){ def bar1(f : Foo) : Boolean def bar2(f : Foo) : Foo } multiple classes extend Foo and override the methods class FooImpl(...) extends Foo{ override def bar1(f : Foo) : Boolean { ... } override def bar2(f : Foo) : Foo { ... } } Is it possible, using generics (or something) to make the overriding methods have the parametertype of the subclass implementing it? Like this : class FooImpl(...) extends Foo{ override def bar1(f : FooImpl) : Boolean

Polymorphic method in Constructor (Java)

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Class A calls the public method f() in the Constructor. Class B overrides method f() with its own implementation. Suppose you intantiate Object B .. method f() of Object B would be called in the Constructor of Object A , although Object B is not fully initialized. Can anyone explain this behavior? EDIT: Yes, it's not recommended practice.. yet i don't understand why Java is not calling the f() implementation of the base-Class A instead of "reaching out" to the f() implementation of the derived Class B . Code: class A { A() { System.out.println("A: constructor"); f(); } public void f() { System

Overriding Equals method in Structs

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问题 I've looked for overriding guidelines for structs, but all I can find is for classes. At first I thought I wouldn't have to check to see if the passed object was null, as structs are value types and can't be null. But now that I come to think of it, as equals signature is public bool Equals(object obj) it seems there is nothing preventing the user of my struct to be trying to compare it with an arbitrary reference type. My second point concerns the casting I (think I) have to make before I

How does reflection tell me when a property is hiding an inherited member with the 'new' keyword?

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So if I have: public class ChildClass : BaseClass { public new virtual string TempProperty { get; set; } } public class BaseClass { public virtual string TempProperty { get; set; } } How can I use reflection to see that ChildClass is hiding the Base implementation of TempProperty? I'd like the answer to be agnostic between c# and vb.net We'll have to deal in terms of the methods of the property here rather than the property itself, because it is the get/set methods of the property that actually get overridden rather than the property itself. I'll use the get method as you should never have a

Android Activity which overridden functions must call super.*

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问题 When creating own Activity subclass, we are overriding some of the basic Activity lifecycle functions. In which of these we must call super implementation, where we should and where is it only good manner ? // base lifecycle onCreate(Bundle savedInstanceState); onStart(); onRestart(); onResume(); onPause(); onStop(); onDestroy(); finalize(); onUserLeaveHint(); // instance state onSaveInstanceState(Bundle outState); onRestoreInstanceState(Bundle savedInstanceState) // others

Specifying the return type of an abstract method from a Base Class according to a Sub Class

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I have the following structure: abstract class Base { public abstract List<...> Get(); //What should be the generic type? } class SubOne : Base { public override List<SubOne> Get() { } } class SubTwo : Base { public override List<SubTwo> Get() { } } I want to create an abstract method that returns whatever class the concrete sub class is. So, as you can see from the example, the method in SubOne should return List<SubOne> whereas the method in SubTwo should return List<SubTwo> . What type do I specify in the signature declared in the Base class ? [UPDATE] Thank you for the posted answers. The

How to override a column in Rails model?

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I have a model for one of my database tables. I want to override the column name for that particular table. How would I achieve it. For example, let my table be called DUMMY and it has one column called col_a col_a 20 34 42 23 12 I would be doing a @dummy.col_a . Now this method should return me 0 for numbers ending with 0 and for everything else, it should return the original value. I could do that by defining a new method, but I want to override the column name itself. Please help. You can override the col_a method. Use the read_attribute method to read the value in database. Something like