null

What are the advantages of using nullptr?

由 浪子不回头ぞ 提交于 2019-12-27 10:33:04
问题 This piece of code conceptually does the same thing for the three pointers (safe pointer initialization): int* p1 = nullptr; int* p2 = NULL; int* p3 = 0; And so, what are the advantages of assigning pointers nullptr over assigning them the values NULL or 0 ? 回答1: In that code, there doesn't seem to be an advantage. But consider the following overloaded functions: void f(char const *ptr); void f(int v); f(NULL); //which function will be called? Which function will be called? Of course, the

What is the correct way to represent null XML elements?

由 百般思念 提交于 2019-12-27 10:31:54
问题 I have seen null elements represented in several ways: The element is present with xsi:nil="true" : <book> <title>Beowulf</title> <author xsi:nil="true"/> </book> The element is present, but represented as an empty element (which I believe is wrong since 'empty' and null are semantically different): <book> <title>Beowulf</title> <author/> </book> <!-- or: --> <book> <title>Beowulf</title> <author></author> </book> The element is not present at all in the returned markup : <book> <title

What are the advantages of using nullptr?

由 家住魔仙堡 提交于 2019-12-27 10:30:33
问题 This piece of code conceptually does the same thing for the three pointers (safe pointer initialization): int* p1 = nullptr; int* p2 = NULL; int* p3 = 0; And so, what are the advantages of assigning pointers nullptr over assigning them the values NULL or 0 ? 回答1: In that code, there doesn't seem to be an advantage. But consider the following overloaded functions: void f(char const *ptr); void f(int v); f(NULL); //which function will be called? Which function will be called? Of course, the

Which is preferred: Nullable<T>.HasValue or Nullable<T> != null?

由 吃可爱长大的小学妹 提交于 2019-12-27 09:52:08
问题 I always used Nullable<>.HasValue because I liked the semantics. However, recently I was working on someone else's existing codebase where they used Nullable<> != null exclusively instead. Is there a reason to use one over the other, or is it purely preference? int? a; if (a.HasValue) // ... vs. int? b; if (b != null) // ... 回答1: The compiler replaces null comparisons with a call to HasValue , so there is no real difference. Just do whichever is more readable/makes more sense to you and your

（原）list中null的谨慎使用

由 一笑奈何 提交于 2019-12-27 03:04:27
今天在刷算法题时，新建了ArrayList变量，发现ArrayList与null结合起来使用时经常出错。 请查看如下几种例子， 1、new一个ArrayList<>类型的数据， 1 import java.util.ArrayList; 2 3 public class Test 4 { 5 6 @SuppressWarnings("unused") 7 public static void main(String[] args) 8 { 9 ArrayList<Integer> al=new ArrayList<Integer>(); 10 //al.add(null); 11 //al=null; 12 if (al==null) 13 { 14 System.out.println("al==null"); 15 } 16 17 if (al.isEmpty()) 18 { 19 System.out.println("al is Empty"); 20 } 21 22 23 System.out.println("al.size(): "+al.size()); 24 25 System.out.println("al.get(0): "+al.get(0)); 26 al.add(5); 27 al.add(4); 28 } 29 } 2、将ArrayList<

Collection常用子类源码阅读-List子类篇:LinkedList

由 左心房为你撑大大i 提交于 2019-12-26 17:11:41
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 类图关系: LinkedList底层存储数据结构： private static class Node<E> { //当前元素存储的值 E item; //当前元素的前一个元素 Node<E> next; //当前元素的下一个元素 Node<E> prev; Node(Node<E> prev, E element, Node<E> next) { this.item = element; this.next = next; this.prev = prev; } } LinkedList的属性变量： //长度 transient int size = 0; //第一个元素 transient Node<E> first; //最后一个元素 transient Node<E> last; 一、构造方法： LinkedList的构造方法，除了一个无参构造方法，还有一个以Collection 实例为入参的构造方法，内部调用了allAll(Collection实例)方法，后面再细说吧。看过LinkedList的底层数据结构和属性变量之后，在这里需要细说一下LinkedList的结构： 一个Node节点对象，它的next属性引用指向下一个节点，prev属性引用指向上一个节点，因此节点与节点之间形成一个链表的结构

AS3: Error 1009:

由 对着背影说爱祢 提交于 2019-12-26 07:45:13
问题 In a little game I have to make for college I render a menu at runtime, using movieclips i made of buttons i drawed in illustrator. I imported the illustrator file in flash professional like I always do, and made a AS linkage like I do with my other movieclips that run fine. But when I try to render these buttons I get a error 1009, a null reference. I use AS3 by the way. private function initMenuComponents():void{ var btnPlay:MovieClip = new Play(); var btnOptions:MovieClip = new Options();

AS3: Error 1009:

由 ￡可爱￡侵袭症＋ 提交于 2019-12-26 07:44:58
问题 In a little game I have to make for college I render a menu at runtime, using movieclips i made of buttons i drawed in illustrator. I imported the illustrator file in flash professional like I always do, and made a AS linkage like I do with my other movieclips that run fine. But when I try to render these buttons I get a error 1009, a null reference. I use AS3 by the way. private function initMenuComponents():void{ var btnPlay:MovieClip = new Play(); var btnOptions:MovieClip = new Options();

AS3: Error 1009:

由 狂风中的少年 提交于 2019-12-26 07:44:11
问题 In a little game I have to make for college I render a menu at runtime, using movieclips i made of buttons i drawed in illustrator. I imported the illustrator file in flash professional like I always do, and made a AS linkage like I do with my other movieclips that run fine. But when I try to render these buttons I get a error 1009, a null reference. I use AS3 by the way. private function initMenuComponents():void{ var btnPlay:MovieClip = new Play(); var btnOptions:MovieClip = new Options();

AS3: Error 1009:

由 你。 提交于 2019-12-26 07:42:06
问题 In a little game I have to make for college I render a menu at runtime, using movieclips i made of buttons i drawed in illustrator. I imported the illustrator file in flash professional like I always do, and made a AS linkage like I do with my other movieclips that run fine. But when I try to render these buttons I get a error 1009, a null reference. I use AS3 by the way. private function initMenuComponents():void{ var btnPlay:MovieClip = new Play(); var btnOptions:MovieClip = new Options();
订阅 null