instanceof

前言: undefined表示 "未定义", null 表示 "空" 第一步: 一般在变量或属性没有声明或者声明以后没有赋值时, 这个变量的值就是undefined; typeof a; // "undefined"; var b; typeof(b); // "undefined"; var c = {}; typeof(c.name); // "undefined"; 第二步: null是检测变量指向的内存地址是否存在, 即: 如果变量不指向任何一个内存地址, 则返回null. document.getElementById("fasdf") // null Object.prototype.__proto__; // null 注意: null 和 undefined 都是基本类型, 使用instanceof检测类型时都会返回false; 但null非常特殊, 使用typeof去判断时会返回object, 但是有instanceof判断时又会返回false; 一般判断某个变量是否为null, 使用的是: null === null; null instanceof Object; // false undefined instanceof Object; // false typeof null; // "object"; typeof undefined; //

前言: 判断基本类型用: typeof, 判断引用类型用: instanceof 注意: 1. typeof可以当关键字使用, 也可以当函数使用, 它可以检测基本类型, 但无法检测引用类型. 2. instanceof 只能作关键字使用, 可以检测引用类型, 不能检测基本类型. 第一步: typeof 的使用方法 typeof 1; // "number"; typeof true; // "boolean"; typeof "hello"; // "string"; typeof []; // "object"; typeof console; // "object"; typeof {}; // "object" 注意: 上面的代码告诉我们, typeof只能检测基本类型, 不能检测引用类型(全返回object); 第二步: instanceof 的使用方法 instanceof 可以检测引用类型, 其实际含义是: 检测某个实例是否是某个构造函数的实例 console.log([] instanceof Array); // true; console.log({} instanceof Object); // true; console.log([] instanceof Object); // true; console.log(console.log instanceof

I'm writing a piece of code in which I have to cast an Object if it is an instance of a certain class. As usual I'm using instanceof for checking the compatibility. The problem is that the check is never satisfied because the objects belong to "strange" classes. For example; when I call the method getClass().getSimpleName() on this object it return me the name of the class + $* (e.g. ViewPart$1 instead of ViewPart ). What does this $* means? Is there a solution or a workaround? That shows an inner class (either anonymous (if it has a number) or named). For example: class Foo { static class Bar

I'm trying to write a job scheduling system in GWT that maintains an array of exceptions ( Class<? extends Exception>[] exceptions ), that might be resolved by retrying the job. For this, if the scheduler catches an exception, I need to see if this exception matches one of the classes in the array. So, I would like to have a function like this: boolean offerRetry(Exception exception) { for (Class<? extends Exception> e: exceptions) if (e.isInstance(exception)) return true; return false; } Unfortunately Class.isInstance(...) isn't available in GWT. Is there a good work-around for this? My

Trying determinate DOM Element by simple check isElement = SomeThing instanceof Element works in main document, but not on (all?) nodes in iframe. Example output (Google Chrome): (mdiv is DIV in main document, idiv is DIV in iframe) OMGWTF ok: mdiv instanceof Element ... true ... [object HTMLDivElement] ok: mdiv instanceof Object ... true ... [object HTMLDivElement] ko: idiv instanceof Element ... false ... [object HTMLDivElement] KO : idiv instanceof Object ... false ... [object HTMLDivElement] There are different javascript implementations for main document and for iframe documents ???

All of our typescript classes inherit (directly or indirectly) from: export class WrObject { className:string; public instanceOf(name : String) : boolean { return this.className === name; } } We then declare a subclass as: export class Section extends WrObject { public static CLASS_NAME = 'Section'; className = Section.CLASS_NAME; public instanceOf(name : String) : boolean { if (this.className === name) return true; return super.instanceOf(name); } } And you can then check with: if (obj.instanceOf(Section.CLASS_NAME)) It all works great. However, I think it would be cleaner if we could do: if

public class OkGoUtils { /** * 必须在Application中初始化 * @param context Application对象 * @author LH * created at 2019/9/25 10:23 */ public static void init(Application context){ OkHttpClient.Builder builder = new OkHttpClient.Builder(); HttpLoggingInterceptor loggingInterceptor = new HttpLoggingInterceptor("OkGo"); loggingInterceptor.setPrintLevel(HttpLoggingInterceptor.Level.BODY); //log打印级别，决定了log显示的详细程度 loggingInterceptor.setColorLevel(Level.INFO); //log颜色级别，决定了log在控制台显示的颜色 builder.addInterceptor(loggingInterceptor); //添加OkGo默认debug日志 builder.readTimeout(10000, TimeUnit.MILLISECONDS); //全局的读取超时时间

自定义注解@ExcelField package cn.lisongyu.common.annotation; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; /** * @author lisongyu * @date 2019/09/23 */ @Target({ElementType.FIELD, ElementType.METHOD, ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) public @interface ExcelField { /** * 导出字段名（默认调用当前字段的“get”方法，如指定导出字段为对象，请填写“对象名.对象属性”，例：“area.name”、“office.name”） */ String value() default ""; /** * 导出字段标题（需要添加批注请用“**”分隔，标题**批注，仅对导出模板有效） */ String title(); /** * 导出字段对齐方式（0：自动；1：靠左；2