properties | 易学教程

What happens with Unused Class Properties

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问题 I am interested to know what happens with unused properties of a class when an object is instantiated? Are there performance hits for having additional unused properties? What about complex properties that are accessing the database, but I'm not using them, are they still being loaded? 回答1: Yes, they are still in memory with default values for the types. Any property sets called will increase memory usage on reference types, whether get is called or not. 来源： https://stackoverflow.com

DropDownList holds one more value

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问题 I have dropdownlist which has items that text and value property of the item are set to primary key. Yes, I show primary key with text property and querying with value property. I want also to get selected item's other property such as name without querying dataset that binds to dropdownlist or querying database. How can I do that? <asp:DropDownList ID="ddl" runat="server"> <asp:ListItem Text="ItemID" Value="ItemID"></asp:ListItem> // I want get item's name </asp:DropDownList> 回答1:

Truncating takes too much time hsqldb

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问题 I use HSQLDB 2.3.2 and I've got the following issues: My database has cached table with 10 000 000 records without any constraints and indexes. Its size is about ~900mb. I turn off autocommit mode and when I try to execute "Truncate table tableName", execution hangs but only dbName.backup is growing. And here's why: TRACE ENGINE:? - copyShadow [size, time] 2246252 9721 TRACE ENGINE:? - setFileModified flag set TRACE ENGINE:? - cache save rows [count,time] totals 24801,9921 operation 24801

Mybatis配置文件

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Objective-C Overwrite only non-nil properties

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问题 Let's say I have a class Car , with the following property scheme: @interface Car : NSObject @property int carID; @property Driver *driver; @property NSString *brandName; ... @end Now, I have a dictionary of Car instances, and whenever I download a new instance from my server, I overwrite with carDictionary[@(newCar.carID)] = newCar; to keep my instances updated. The only issue is that sometimes my instances are downloaded with some properties not filled out. When I download a new instance,

IDEA开发spring boot应用时 application.yml 或 application.properties 自定义属性提示

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/*--> */ /*--> */ 在使用spring boot开发过程中，经常会定义一些应用自己的属性，直接写到application配置文件中使用@Value注解进行使用，这样使用也没有什么问题。不过我认为更优雅的方式是定义自己的属性类统一管理，这样在idea中，既能自动提示，又能对配置进行分类管理，显得有条不紊，下面是具体的配置步骤。第一步：添加依赖（分为maven和gradle两种方式） 1.1 如果你使用的是maven 增加依赖 <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-configuration-processor</artifactId> </dependency> 1.2 如果你使用的是gradle 增加依赖并且配置annotationProcessor compileOnly 'org.springframework.boot:spring-boot-configuration-processor' annotationProcessor ‘org.springframework.boot:spring-boot-configuration-processor’ 第二步：创建配置属性类 @Data

How to alter title bar height for access form?

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问题 Is there a way of altering the title bar height for a form (actually a subform) when it is displayed in datasheet mode? My field titles are often longer than the data and there is not very much I can do about this. It's not a problem when the form is in 'Single Form' view, but there will be lots of times when the datasheet view is helpful, because it's a good summary of info. I had thought that forcing a new line in the field title might work, but it doesn't. 回答1: Access does not allow for

What is the differect between word-wrap and overflow-wrap? [duplicate]

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问题 This question already has an answer here : Difference between overflow-wrap and word-break? (1 answer) Closed 3 years ago . Can someone please help me to figure out the different between those two css properties. I thinks its seem to be same. Please help me out. Thank in advance. 回答1: Yes both are same. You may follow this article about this topic. Dealing with long words in css 来源： https://stackoverflow.com/questions/39596704/what-is-the-differect-between-word-wrap-and-overflow-wrap

Java笔记--集合

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1、Java集合类可以用于存储数量不等的多个对象，还可以用于保存具有映射关系的关联数组。 2、Java集合可分为Collection和Map两种体系： --Collection:1)Set:元素无序、不可重复的集合；2)List:元素有序，可重复的集合 --Map:具有映射关系"key/value对"的集合。 3、Collection接口：　　|----List接口：　　　　|----ArrayList、LinkedList、Vector 　　|----Set接口：　　　　|----HashSet、LinkedHashSet、TreeSet Map接口：　　|----HashMap、LinkedHashMap、TreeMap、HashTable(子类：Properties) 4、Collection接口中定义的常用方法： --add(Object o);//添加对象； --addAll(Collection col);//将集合col里面的元素全部添加到当前集合； --clear();//清空当前集合; --contains(Object o);//判断当前结合是否包含对象o； --containsAll(Collection col);//判断当前集合是否包含集合col中的所有对象； --isEmpty();//判断当前集合是否为空； --remove(Object o)

Why do classes need to be “final” when adopting a protocol with a property with type “Self”?

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问题 I can use generic protocols just fine, but am trying to grasp the reasoning behind some limitations of generic protocols. Example: internal protocol ArchEnemyable { var archEnemy: Self? { get } } internal final class Humanoid: ArchEnemyable { internal var archEnemy: Humanoid? // is the adoption to Self, works only when class is final internal init(otherOne pOtherOne: Humanoid?) { self.archEnemy = pOtherOne } } I do not find any example where it would not work, when it is not final. Do one of