class | 易学教程

Java Object Oriented Design: Returning multiple objects in java

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问题 The below code in Java throws Null pointer exception. public class New{ int i; New(int i) { this.i = i; } public void func(New temp) { temp.i = 10; temp = new New(20); } public static void main(String[] args) { New n = null; n.func(n); System.out.println("value "+ n.i); } } The reason being, java passes objects references by value. If I wanted to return one object, then I can return it from the function. But, If I have multiple objects, the only way I could return the object references is, by

Search based on list item class

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问题 I'm not too familiar with anything beyond writing markup and CSS, and I have a question.. If I have one .html page with a structure like this: <ul> <li></li> <li></li> <li></li> </ul> Now let's assume each of these list items has a class assigned to it, but the class is not unique, and is used multiple times. Is it possible to fetch all list items based on a certain class to another .html page? For example, summon all list items with class "red" to a page called red.html, and all items with

Vue.js: Import class with function and call it in child component

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问题 I have a component my-parent . In this component, I use a child component my-child and import an external class MyClass with an own function exportedFunction . I tried to use this solution: VueJS accessing externaly imported method in vue component Basiclly, I use mounted and the name of the function from the imported class. In methods I defined a new method, which calls the mounted one from the imported class. Than I pass the created method as property to my child, where I try to call the

python爬虫实践——爬取“豆瓣top250”

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1 ''' 2 主页: 3 https://movie.douban.com/top250 4 GET 5 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.146 Safari/537.36 6 7 re正则: 8 # PS: 电影详情页url、图片链接、电影名称、导演、主演、电影上映时间、电影评分、评价人数、简介 9 <div class="item">.*?href="(.*?)">.*?src="(.*?)" class="">.*?<span class="title">(.*?)</span>.*?导演:(.*?).*?主演: (.*?) /...<br>(.*?)</p>.*?content="(.*?)"></span><span>(.*?)人评价.*?<span class="inq">(.*?)</span> 10 ''' 11 ''' 12 每一页URL: 13 第一页：https://movie.douban.com/top250 14 第二页：https://movie.douban.com/top250?start=25&filter= 15 第三页：https://movie.douban

Creating dynamic POJOs and set values to it

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问题 final Map<String, Class<?>> properties = new HashMap<String, Class<?>>(); properties.put("jobName", String.class); properties.put("companyName", String.class); properties.put("totalApplicantForJob", String.class); final Class<?> beanClass = createBeanClass("ApplicantCountVsJobBoards", properties); public static Class<?> createBeanClass (final String className, final Map<String, Class<?>> properties) { final BeanGenerator beanGenerator = new BeanGenerator(); // NamingPolicy policy = /

python: comparing 2 lists of instances

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问题 I have 2 lists of instances: list1 list2 each instance contains variables such as id, name, etc... I am iterating through list2, and I want to find entries that don't exist in list1. eg.. for entry in list2: if entry.id in list1: <do something> I'm hoping to find a way to do this without a douple for loop. Is there an easy way? 回答1: I might do something like: set1 = set((x.id,x.name,...) for x in list1) difference = [ x for x in list2 if (x.id,x.name,...) not in set1 ] where ... is additional

Recursive class C#

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问题 Can I define constructor like this? Additional question: Can I call constructor of the class in itself constructor? class SubArray { List<int> array; string parent; string name; SubArray child; public SubArray(SubArray child, string name) { this.child = child; List<int> array = new List<int>(); this.name = name; } } 回答1: There is no limit on that, but like any recursion - it needs a stopping condition. otherwise it will cause a stack overflow (PUN intended :)). 回答2: I guess you could do

Swift - Type has no member

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问题 I have a basic class named APIGroup that exists for the sole purpose of subclassing (it is not [yet] used for anything but certain static properties that are accessed by the subclasses). It looks somewhat like this: public class APIGroup { public static let someProperty : String = "I am a property!" } And I have a subclass, Track , which defines a type method search as follows: public class Track : APIGroup { public static func search(name: String) -> Void { print("Track search initiated.

python爬虫1

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>>> import requests >>> r=request.get("http://www.baidu.com") >>> type(r) <class 'requests.models.Response'> >>> >>> r.status_code 200 >>> 连接成功 >>> r.text '<!DOCTYPE html>\r\n<html> <head><meta http-equiv=content-type content=text/html;charset=utf-8><meta http-equiv=X-UA-Compatible content=IE=Edge><meta content=always name=referrer><link rel=stylesheet type=text/css href=http://s1.bdstatic.com/r/www/cache/bdorz/baidu.min.css><title>ç\x99¾åº¦ä¸\x80ä¸\x8bï¼\x8cä½\xa0å°±ç\x9f¥é\x81\x93</title></head> <body link=#0000cc> <div id=wrapper> <div id=head> <div class="head_wrapper">

Why can't I declare and initialize static variable in inner class? [duplicate]

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问题 This question already has answers here : Why does Java prohibit static fields in inner classes? (8 answers) Closed 3 years ago . class A is the outer class. Class B is an inner class of A, and class C is an inner class of B. All three classes declare and initialize one static final variable. This is the object in class A: static final Object x = new Object(); class B: static final Object x1 = new Object(); class C: static final Object x2 = new Object(); The problem is that the variable in