Check if object is of type String [duplicate]

You can empty an object by setting it to : Example let person = ; person = null; // Now value is null, but type is still an object Try it Yourself » You can also empty an object by setting it to : Example let person = ; person = undefined; // For primitive types there is no solution available as the problem of knowing the type stored in a variable does not exist.

Typeof in Java 8

If we want to check the datatype of variable in javascript, we can use typeof operator .

Consider this snippet

var c = 'str' ; console.log(typeof(c)); // string c = 123 ; console.log(typeof(c)); // number c = <> ; console.log(typeof(c)) ; // object 

I want to achieve the same functionality in Java 8 . Java does not have typeof operator but there’s the instanceof operator to check the types.

System.out.println("str" instanceof String); // true Integer a = 12 ; System.out.println(a instanceof Integer); Float f = 12.3f System.out.println(f instanceof Float); // true 

Can we do any better ? Plus instanceof does not support primitive types .

Is there any approaches in java 8 ? Any relevant approaches will be appreciated.

You can use the getClass() method to get the type of the object you are using:

Object obj = null; obj = new ArrayList(); System.out.println(obj.getClass()); obj = "dummy"; System.out.println(obj.getClass()); obj = 4; System.out.println(obj.getClass()); 

This will generate the following output:

class java.util.ArrayList class java.lang.String class java.lang.Integer 

As you see it will show the type of the object which is referenced by the variable, which might not be the same as the type of the variable ( Object in this case).

For primitive types there is no solution available as the problem of knowing the type stored in a variable does not exist. A primitive type variable can hold only values of that type. As you have to define the variable (or parameter) somewhere you already know the type of it and the values it can hold. There is no «base» type for primitive values which you can use similar to the Object type, which is the base type for all objects in java.

Thanks to @Progman for getClass() method .

class check < static Class typeof(Integer a) < return a.getClass(); >static Class typeof(Character c) < return c.getClass(); >static Class typeof(Float f) < return f.getClass(); >static Class typeof(Double d) < return d.getClass(); >static Class typeof(Long l) < return l.getClass(); >static Class typeof(String s) < return s.getClass(); >> 

So now we check both primitive and non- primitive types

check.typeof(12) ; // class java.lang.Integer

check.typeof(12.23f) ; // class java.lang.Float

check.typeof(‘c’) ; // class java.lang.Character

check.typeof(«str») ; // class java.lang.String

This is the closest functionality example I could find in Java (10 or higher) to your JavaScript example with the typeof operator and var ( local variable declaration only in Java).

It deals with primitive data type and implies casting the primitive to Object first and then calling the .getClass().getSimpleName() method on the respective Object.

JavaScript String (with Examples), The String () function is used to convert various data types to strings. For example, const a = 225; // number const b = true; // boolean //converting to string const …

Check if object is of type String [duplicate]

I need to write a new method that checks if certain values are of the type String or not.

I have two objects and I want to be able to check if these two objects are strings, if they are to then return true, and false otherwise.

I did start off with the following method:

public boolean stringTest()

But could not get anything to work after that, any help would be greatly appreciated!

You can make use of instanceof and rewrite your method

public boolean stringTest(Object any)

stringTest(townName); // true stringTest(new Integer()); // false 

public boolean isString(Object o)

Javascript if typeof string Code Example, Get code examples like «javascript if typeof string» instantly right from your google search results with the Grepper Chrome Extension. Grepper. Follow. GREPPER; …

JavaScript typeof

In JavaScript there are 5 different Data Type s that can contain values:

There are 6 types of objects:

And 2 data types that cannot contain values:

The typeof Operator

You can use the typeof operator to find the data type of a JavaScript variable .

Example

typeof «John» // Returns «string»
typeof 3.14 // Returns «number»
typeof NaN // Returns «number»
typeof false // Returns «boolean »
typeof [1,2,3,4] // Returns «object»
typeof // Returns «object »
typeof new Date() // returns «object »
typeof function () <> // Returns «function»
typeof myCar // Returns «undefined » *
typeof null // Returns «object»

• The data type of NaN is number
• The data type of an array is object
• The data type of a date is object
• The data type of null is object
• The data type of an undefined variable is undefined *
• The data type of a variable that has not been assigned a value is also undefined *

You cannot use typeof to determine if a JavaScript object is an array (or a date).

Primitive Data

A primitive data value is a single simple data value with no additional properties and methods.

The typeof operator can return one of these primitive types:

Example

typeof «John» // Returns «string»
typeof 3.14 // Returns «number»
typeof true // Returns «boolean»
typeof false // Returns «boolean»
typeof x // Returns «undefined» (if x has no value)

Complex Data

The typeof operator can return one of two complex types:

The typeof operator returns «object» for objects, arrays , and null.

The typeof operator does not return «object » for functions.

Example

typeof // Returns «object»
typeof [1,2,3,4] // Returns «object» (not «array», see note below)
typeof null // Returns «object»
typeof function myFunc()<> // Returns «function»

The typeof operator returns » object » for arrays because in JavaScript arrays are objects.

The Data Type of typeof

The typeof operator is not a variable. It is an operator. Operators ( + — * / ) do not have any data type.

But, the typeof operator always returns a string (containing the type of the operand).

The constructor Property

The constructor property returns the constructor function for all JavaScript variables .

Example

«John».constructor // Returns function String() <[ native code ]>
(3.14).constructor // Returns function Number() <[native code]>
false.constructor // Returns function Boolean() <[native code]>
[1,2,3,4].constructor // Returns function Array() <[native code]>
.constructor // Returns function Object () <[native code]>
new Date().constructor // Returns function Date() <[native code]>
function () <>.constructor // Returns function Function() <[native code]>

You can check the constructor property to find out if an object is an Array (contains the word «Array»):

Example

Or even simpler, you can check if the object is an Array function :

Example

You can check the constructor property to find out if an object is a Date (contains the word «Date»):

Example

Or even simpler, you can check if the object is a Date function :

Example

Undefined

In JavaScript, a variable without a value, has the value undefined . The type is also undefined .

Example

Any variable can be emptied, by setting the value to undefined . The type will also be undefined .

Example

Empty Values

An empty value has nothing to do with undefined .

An empty string has both a legal value and a type.

Example

Null

In JavaScript null is «nothing». It is supposed to be something that doesn’t exist.

Unfortunately, in JavaScript, the data type of null is an object.

You can consider it a bug in JavaScript that typeof null is an object. It should be null .

You can empty an object by setting it to null :

Example

You can also empty an object by setting it to undefined :

Example

Difference Between Undefined and Null

undefined and null are equal in value but different in type:

typeof undefined // undefined
typeof null // object

null === undefined // false
null == undefined // true

Typeof() java Code Example, Object obj = null; obj = new ArrayList(); System.out.println(obj.getClass()); obj = «dummy»; System.out.println(obj.getClass()); obj = 4; System.out.println

Источник

Java: Determining if an Object is a String or String Array

In JavaScript, an object is an unordered list that contains primitive and reference data types stored as key-value pairs. To check whether a string is of literal or object type, we use the typeof or instanceof methods. For instance, in the index.html file, we can output the results. One common question that arises is how to determine if a column in an object is a string or another type, such as integer or float, despite its dtype being object.

How to check whether an Object is String or String Array in java?

The method is designed to return either Object or Object[] of String type. However, when I try to cast it using String[] , it returns class cast exception instead of a single string. Is there a way to fix this issue?

Is it possible to verify the existence of either String or String[] within it?

Employ the operator labeled as instanceof .

if (x instanceof String) < . >if (x instanceof String[])

Performing this action is not optimal and it would be great if there was an alternative approach to avoid it. Could you possibly modify your API design to facilitate this?

Modify the approach to ensure that String[] is returned every time, even if there is only one.

It would be preferable if the function returns List and utilizes Collections.singletonList() for the scenario when there is only one element.

JavaScript: Check if Variable Is a String, JavaScript supports a variety of data types such as strings, numbers, floats, etc. A string is a collection of characters such as «John Doe».

JavaScript: How to Check if a String is a Literal or an Object?

In the upcoming discussion, we will delve into the versatility of strings, which can be utilized as both a literal and an object to fulfill varying needs.

JavaScript Literals

A JavaScript literal refers to fixed values in source code and typically includes integers, floating-point numbers, strings, booleans, records, and other value types commonly used in programming languages.

JavaScript Objects

Alternatively, a JavaScript data type can be described as an unstructured collection of primitive data types, including reference data types in some cases, stored in a key-value pair format. Each item in the collection is referred to as a property.

The type of Operator

How do we determine if the string is classified as literal or an Object?

To determine the data type of literals, variables, functions, or objects, we will utilize the typeof operator. This operator returns the actual data type of any operand provided.

The operator «instanceof» can be utilized to compare an Object with an instance, which will result in the specific object’s instance being returned.

Example

Below, we will demonstrate how to define a string using both literal and object forms. Then, we will apply either the typeof or instanceof method to confirm whether the string is categorized as a literal or object type.

   
Welcome to Tutorials Point
 

Output

JavaScript: Check if Variable is a Number, Using the typeof() function · undefined · boolean · number · string · bigint · symbol · object · null ( typeof() shows as object)

Check if ENTIRE pandas object column is a string

In what way is it possible for check if a column to be classified as an object, regardless of whether it is a string or any other data type such as int or float?

I prefer the vectorization of this operation instead of applymap that involves checking each row individually.

import io # American post code df1_str = """id,postal 1,12345 2,90210 3,""" df1 = pd.read_csv(io.StringIO(df1_str)) df1["postal"] = df1["postal"].astype("O") # is an object (of type float due to the null row 3) 

# British post codes df2_str = """id,postal 1,EC1 2,SE1 3,W2""" df2 = pd.read_csv(io.StringIO(df2_str)) df2["postal"] = df2["postal"].astype("O") # is an object (of type string) 

object is the output generated by df1 and df2 when performing df[«postal»].dtype .

• While df2 supports .str methods, such as df2[«postal»].str.lower() , df1 lacks them.
• In the same way, df1 is capable of undergoing mathematical operations such as df1 * 2 .

Unlike typical questions on SO that inquire about the presence of strings in a column, this particular inquiry pertains to the entire column itself. For instance:

• In case dataframe column includes string type.
• Check if string is in a pandas dataframe
• Create a column in the dataframe that accepts string values.

You can use pandas.api.types.infer_dtype :

>>> pd.api.types.infer_dtype(df2["postal"]) 'string' >>> pd.api.types.infer_dtype(df1["postal"]) 'floating' 

Effortlessly determine the type of a provided value or an array-like collection of values and provide a descriptive string representation of the type.

Check if a variable is a string in JavaScript, In JavaScript you can have variable type of string or type of object which is class of String (same thing — both are strings — but defined

Источник