instanceof

JavaScript创建对象的7大模式

由 时光总嘲笑我的痴心妄想 提交于 2019-12-15 10:47:59
在JavaScript中，创建对象有7大模式，分别是工厂模式、构造函数模式、原型模式、组合使用构造函数模式和原型模式、动态原型模式、寄生构造函数模式、稳妥构造函数模式。下面针对这7种模式展开讲解。 工厂模式 工厂模式抽象了创建具体对象的过程，用函数来封装以特定接口创建对象的细节。函数createPerson()能够根据接受的参数来构建一个包含所有必要信息的Person对象。可以无数次地调用这个函数，而每次它都会返回一个包含三个属性一个方法的对象。工厂模式虽然解决了创建多个相似对象的问题，但没有解决对象识别的问题。 //1.工厂模式 function createPerson ( name , age , career ) { let o = new Object ( ) ; o . name = name ; o . age = age ; o . career = career ; o . sayName = function ( ) { console . log ( this . name ) ; } return o ; } let person1 = createPerson ( "Febby" , 18 , "student" ) ; let person2 = createPerson ( "Jack" , 22 , "teacher" ) ; console .

Java 继承

由 余生颓废 提交于 2019-12-13 18:20:49
继承是java面向对象编程技术的一块基石，因为它允许创建分等级层次的类。继承可以理解为一个对象从另一个对象获取属性的过程。 如果类A是类B的父类，而类B是类C的父类，我们也称C是A的子类，类C是从类A继承而来的。 在Java中，类的继承是单一继承，也就是说，一个子类只能拥有一个父类 继承中最常使用的两个关键字是extends和implements。 这两个关键字的使用决定了一个对象和另一个对象是否是IS-A(是一个)关系。 通过使用这两个关键字，我们能实现一个对象获取另一个对象的属性。 所有Java的类均是由java.lang.Object类继承而来的，所以Object是所有类的祖先类，而除了Object外，所有类必须有一个父类。 通过过extends关键字可以申明一个类是继承另外一个类而来的，一般形式如下： // A.java public class A { private int i ; protected int j ; public void func ( ) { } } // B.java public class B extends A { } 以上的代码片段说明，B由A继承而来的，B是A的子类。而A是Object的子类，这里可以不显示地声明。 作为子类，B的实例拥有A所有的成员变量，但对于private的成员变量B却没有访问权限，这保障了A的封装性。 IS-A关系

JS 中 typeof instanceof constructor Object.prototype.toString.call()判断数据类型

由 拈花ヽ惹草 提交于 2019-12-13 07:48:36
JS 中 typeof instanceof constructor Object.prototype.toString.call()判断数据类型 JS的数据类型: 基础数据类型和复杂数据类型(引用数据类型) 基础数据类型: number string undefined null boolean symbol 引用数据类型: object 文章目录 JS 中 typeof instanceof constructor Object.prototype.toString.call()判断数据类型 1. typeof 返回一个字符串类型 1. typeof 返回一个字符串类型 MDN介绍 语法 typeof 运算符后接操作数 操作符返回一个 字符串 字符串 字符串 ，表示未经计算的操作数的类型 typeof operand typeof ( operand ) operand 一个表示对象或原始值的表达式，其类型将被返回。 描述 结果 Undefined "undefined" Null "object" Boolean "boolean" Number "number" String "string" Symbol "symbol" Function "function" Object "object" 示例 // 数值 number typeof 1 // "number"

What's faster: instanceof or isInstance?

由 坚强是说给别人听的谎言 提交于 2019-12-13 05:36:19
问题 Design questions aside, what performs faster on modern JVMs? foo instanceof Bar or Bar.class.isInstance(foo) Why? 回答1: Class.isInstance is JVM intrinsic. It is compiled to exactly the same sequence as instanceof does (the proof from HotSpot source code: 1, 2). That is, they both are equal in terms of performance. 回答2: foo instanceof Bar should be faster. You can use Bar.class.isInstance(foo) if it's not clear at compile time which class you have. consider the following: void test(Object o1,

Avoiding instanceof Java

由 主宰稳场 提交于 2019-12-13 05:05:11
问题 I am trying to find a way to bypass the use of instanceof. I've created a class Item which has multiple subclasses like WeaponItem and BodyItem. Now I would like to make to do a call such as equip(Item) and it should determine by itself which overloaded function it should call such as equip(BodyItem). Is there a way to bypass the use of instanceof for this case and what would you recommend? I've heard that in most cases using instanceof is bad practice and therefor I want to know what the

Java: How should look an instanceof method

由 孤街醉人 提交于 2019-12-12 18:29:10
问题 Imagine, I want to write a useless method called: isInstanceof that returns a boolean . I was thinking about it. But I do not get out. An instanceof has to be used like: [object] instanceof [a classname] // I was thinking about something like this public static boolean isInstanceof(Object obj, /*magic for the second param*/) { return obj instanceof /*the magical second param*/ } But how can I make an parameter for [a classname] ? Is there a way to do this without the method isInstance(Class

Boolean instanceof Object is true?

由 ￡可爱￡侵袭症＋ 提交于 2019-12-12 14:03:45
问题 I've been learning Java in my spare time and have a quick question I can't seem to figure out. This code returns true: Boolean testBool = true; Boolean test = testBool instanceof Object; System.out.println(test); However, I thought Boolean was a primitive type and when I try this same logic with any other primitive type I get a compiler error that says: unexpected type required: reference found: int I'm sure there's just something small I'm missing. Thanks for your help! 回答1: boolean is a

instanceof vs isInstance()

由 六眼飞鱼酱① 提交于 2019-12-12 11:07:44
问题 class A{ public A(){ System.out.println("in A"); } } public class SampleClass{ public static void main(String[] args) { A a = new A(); System.out.println(A.class.isInstance(a.getClass())); } } Output: false Why is it false? Both A.class and a.getClass() should not return the same class! And in which condition we will get true from the isInstance() method? 回答1: Because a.getClass() returns Class<A> , but you should pass in an A: System.out.println(A.class.isInstance(a)); If you have two Class

What does this instanceof error message mean?

由 心已入冬 提交于 2019-12-12 07:24:59
问题 I was playing around with instanceof in Chrome but I got an error message. I think I know why (you have to supply a function after the instanceof keyword that is the constructor the object was created with), but the error message seems to be stating something else: [1,2,3] instanceof Array // true [1,2,3] instanceof [] // TypeError: Expecting a function in instanceof check, but got 1,2,3 Does this mean that I should replace [1,2,3] with a function? I would think that [1,2,3] is correct and

How to resolve “unreported exception AWTException ; must be caught or declared to be thrown”. Robot instance

由 ＊爱你＆永不变心＊ 提交于 2019-12-11 06:05:02
问题 I have the error "unreported exception AWTException ; must be caught or declared to be thrown" instantiating a class that contain methods with mouse and key movements using Robot. I tried with try catch In the instance but the "click" doesnt work this way, what is the problem how to solve it? package Ventanas; enter code here import java.awt.AWTException; import java.awt.Robot; import java.awt.event.InputEvent; public class Sel { Robot robot = new Robot(); public void apos() throws
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