class | 易学教程

Inner classes in Java - Non static variable error

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问题 Im still new to java and i tried to create a inner class and call the method inside main. But theres a compilation error saying "Non static variable - This cannot be referenced from a static context" Please help class Class1{ public static void main(String args []){ Class2 myObject = new Class2(); myObject.newMethod(); } public class Class2{ public void newMethod(){ System.out.println("Second class"); } } } 回答1: An inner class needs a reference to an instance of the outer class in order to be

Wrap multiple div elements on same class

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问题 I would like to use jQuery to wrap sets of class elements in a div but can't find the solution. HTML: <div class="view-content"> <div class="first">content</div> <div class="first">content</div> <div class="second">content</div> <div class="third">content</div> <div class="third">content</div> </div> Desired Result: <div class="view-content"> <div class="column"> <div class="first">content</div> <div class="first">content</div> </div> <div class="column"> <div class="second">content</div> <

Access parent's overridden method from parent's context in PHP

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问题 I have a drawing PHP class called ClassA that is extended by many other drawing classes, ClassB for instance. I need the inherited classes to fire its parent classes' Draw() method. However, in my particular situation, I do not want to call such method directly (e.g.: parent::Draw() ). I'd like a third function (e.g.: parent::InvokeDraw() ) to call my drawing method from within the parent's context. Here's some code to illustrate: class ClassA { function Draw() { /* Drawing code ... */ }

Class menu in Tkinter Gui

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问题 I'm working on a Gui and I'd like to know if it is possible to make the menu property of a window a separate class on my script for a clearer and more enhancement prone code. my code currently is : class Application(Frame): """ main window application """ def __init__(self, boss = None): (...) self.menu = Menu(self) self.master.config(menu = self.menu) self.select = Menu(self.menu) self.menu.add_cascade(label = 'Select', menu = self.select) self.select.add_command(label = 'Select all',

Forward Declaration of a Base Class

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问题 I'm trying to create proper header files which don't include too many other files to keep them clean and to speed up compile time. I encountered two problems while doing this: Forward declaration on base classes doesn't work. class B; class A : public B { // ... } Forward declaration on STD classes doesn't work. namespace std { class string; } class A { string aStringToTest; } How do I solve these problems? 回答1: The first problem you can't solve. The second problem is not anything to do with

02 前端篇（选择器和属性）

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http 协议：超文本传输协议，基于请求 / 响应模式无状态协议（短连接，无记忆） url ：统一资源定位符 post 有请求体， get 没有请求体 referer ：请求来自那个页面。放在请求头部 Content-Type ： url 编码方式，放在请求体里面的 css ： Cascoding Style Sheets ，层叠样式表四种引入方式 : 行内式嵌入式链接式（推荐）导入式 css 的选择器（ selector ）：基础选择器： * 通用元素选择器 E 标签选择器 .info 和 E.info ： class 选择器。匹配所有 class 属性中包含 info 的元素 .info {color: Yellow} p.info {color: Yellow} #info ： id 选择器组合选择器： E,F ：多元素选择器，同时匹配所有 E 元素或 F 元素，用逗号分隔 E F ：后代元素选择器，匹配所有属于 E 元素后代的 F 元素， E 和 F 之间用空格分隔 E>F ：子元素选择器，匹配所有 E 元素的子元素 F E+F ：毗邻元素选择器。匹配所有紧随 E 元素之后的同级元素 F 属性选择器： E[att] ：匹配所有具有 att 属性的元素，不考虑它的值 E[att=val] ：匹配所有 att 属性等于 val 的元素 E[att~=val]

PHP PDO-MYSQL : How to use database connection across different classes

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问题 I'm kinda new to PDO with MYSQL, here are my two files: I have a connection class that I use to connect to the database: class connection{ private $host = 'localhost'; private $dbname = 'devac'; private $username = 'root'; private $password =''; public $con = ''; function __construct(){ $this->connect(); } function connect(){ try{ $this->con = new PDO("mysql:host=$this->host;dbname=$this->dbname",$this->username, $this->password); $this->con->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE

bootstrap轮播图

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< div id = "carousel-example-generic" class = "carousel slide" data - ride = "carousel" > < ! -- Indicators -- > < ol class = "carousel-indicators" > < li data - target = "#carousel-example-generic" data - slide - to = "0" class = "active" > < / li > < li data - target = "#carousel-example-generic" data - slide - to = "1" > < / li > < li data - target = "#carousel-example-generic" data - slide - to = "2" > < / li > < / ol > < ! -- Wrapper for slides -- > < div class = "carousel-inner" role = "listbox" > < div class = "item active" > < img src = "..." alt = "..." > < div class = "carousel

Java: where do static fields live within the memory?

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问题 If we store objects in static fields of an object, how does the JVM allocate the memory for it? Does it live within "implicit"(not sure if I am using the right word) class object? How are static fields different from object fields? 回答1: Static fields are class variables, and are shared amongst all instances of that class. Instance variables (or object fields as I think you are referring to them as) belong to individual instances of a class and are not shared. As for where they are stored in

CSS class priorities

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问题 I have a question about the priority of CSS classes after encountering a problem today. The situation is as follows: I have an unordered list which has a class associated with it. The LI tags have some styles defined too. I want to change the styling of the LI s after a click (via an added "selected" class), but the added class's styles are never applied. Is this normal behavior or should this code work? CSS: .dynamicList { list-style: none; } .dynamicList li { display: block; width: 400px;