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Questions tagged [instanceof]

instanceof is an operator available in some object-oriented languages, including Java, php and JavaScript. Generally speaking, it allows the programmer to check whether an object passed as its left operand is an instance of a class specified by the right operand.

instanceof is an operator available in some object-oriented languages, including Java, php and JavaScript. It allows the programmer to check whether an object passed as its left operand is an instance of a class specified by the right operand.

instanceof in Java

instanceof in php

instanceof in JavaScript

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How to efficiently check if variable is Array or Object (in NodeJS & V8)?

Is there any way to efficiently check if the variable is Object or Array, in NodeJS & V8? I'm writing a Model for MongoDB and NodeJS, and to traverse the object tree I need to know if the object is simple (Number, String, ...) or composite (Hash,…
Alex Craft
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instanceof negation

Which is the correct format for negating instanceof? if ( ! $a instanceof stdClass) or if ( ! ($a instanceof stdClass) ) I've convinced myself the latter is correct way, probably after reading a blog article several years ago, but after some…
Mathew
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How instanceof will work on an interface

instanceof can be used to test if an object is a direct or descended instance of a given class. instanceof can also be used with interfaces even though interfaces can't be instantiated like classes. Can anyone explain how instanceof works?
developer
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Avoiding 'instanceof' in Java

I have the following (maybe common) problem and it absolutely puzzles me at the moment: There are a couple of generated event objects which extends the abstract class Event and I want to divide them to Session Beans, like public void…
fnst
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How to "instanceof" a primitive string (string literal) in JavaScript

In JavaScript, I can declare a string in the following ways; var a = "Hello World"; var b = new String("Hello World"); but a is not an instance of String... console.log(a instanceof String); //false; console.log(b instanceof String); //true; So…
Matthew Layton
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Does instanceof return true if instance of a parent?

I have a class Child that extends Parent. Parent child = new Child(); if (child instanceof Parent){ // Do something } Does this return true or false, and why?
ikbal
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How to determine if an object is an instance of certain derived C++ class from a pointer to a base class in GDB?

I'm debugging a C++ program with GDB. I have a pointer to an object of certain class. The pointer is declared to be of some super class which is extended by several sub-classes. There is no fields in the object to specify the precise class type of…
user1101096
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instanceof - incompatible conditional operand types

The following compiles fine: Object o = new Object(); System.out.println(o instanceof Cloneable); But this doesn't: String s = new String(); System.out.println(s instanceof Cloneable); A compiler error is thrown. What is the problem?
java_geek
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Check if an object is an instance of a class (but not an instance of its subclass)

For this example: public class Foo{} public class Bar extends Foo{} .... void myMethod(Foo qux){ if (checkInstance(qux,Foo.class)){ .... } } How can I check if qux is an instance of Foo (but not an instance of its subclass of foo)?…
Addev
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Switch by class (instanceof) in PHP

It is possible to replace block of if( .. instanceof ...), elseif(... instanceof ...), ... with switch? For example:
leninzprahy
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PHP check for instance of DateTime?

Is this the only way to check if an object is an instance of a class, in my case of the DateTime class? $cls = ReflectionClass("DateTime"); if (! $cls->isInstance( (object) $var ) ) { // is not an instance } It seems a bit heavy to me.
Niklas R
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What's the difference between isPrototypeOf and instanceof in Javascript?

In some of my own older code, I use the following: Object.prototype.instanceOf = function( iface ) { return iface.prototype.isPrototypeOf( this ); }; Then I do (for example) [].instanceOf( Array ) This works, but it seems the following would do…
Steffen Heil
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Java - null instanceof Object evaluates to both true and false

When I compile and run this code: public class Testing { public static void main(String... args) { Object obj = null; if (obj instanceof Object) { System.out.println("returned true"); } else { …
Infiniteh
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What's the point of new String("x") in JavaScript?

What are the use cases for doing new String("already a string")? What's the whole point of it?
Pacerier
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How to avoid 'instanceof' when implementing factory design pattern?

I am attempting to implement my first Factory Design Pattern, and I'm not sure how to avoid using instanceof when adding the factory-made objects to lists. This is what I'm trying to do: for (Blueprint bp : blueprints) { Vehicle v =…
Charles H
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