What's the Java equivalent of defining a classless object in JavaScript?

Question

I'm wondering if I can declare an object in-line in Java like I can in JavaScript. For example, in JavaScript I could say

let nameOfObject = {
    anyKey: "my value",
    someOtherValue: 5
};

console.log(nameOfObject.anyKey);// This logs "my value"

and this will create a classless object and assign nameOfObject as its "pointer" of sorts... How can I do this in Java? How do I create an object without a class?

I found one possible solution which looks like

Object nameOfObject = new Object(){
    public String anyKey = "my value";
    public int someOtherValue = 5;
};

System.out.println(nameOfObject.anyKey);

But that doesn't seem to compile, and says "anyKey cannot be resolved" and according to some other sources, will not work at all...

So I might be doing something very wrong, or maybe there's a different method, or maybe it's just straight up not possible with Java and I need to do it a different way...

class Some{
    public String anyKey;
}

Some some = new Some() {
    this.anyKey = "my value";
};

This code throws an error saying Syntax error, insert ";" to complete declaration, however

class Some{
    public void anyMethod() {
        
    }
}
        
Some some = new Some() {
    public void anyMethod() {
        System.out.println("Okay");
    }
};

Works perfectly fine?

I don't understand what's going on here, but I would really appreciate an explanation and/or a solution (if one exists).

Although it is possible to declare a local variable like this in Java 10+, it is not idiomatic Java, and only limited to local variables. Directly translating code from one programming language to another (just like directly translating text from one natural language to another) is almost always a bad idea. — Sweeper
– Sweeper, Commented Jan 8, 2021 at 7:09
java is not javascript. And while some constructs might work in similar fashion, it is definitely not good practice to do so. — rkosegi
– rkosegi, Commented Jan 8, 2021 at 7:10
What is the actual problem that you are trying to solve by creating such an object? — Sweeper
– Sweeper, Commented Jan 8, 2021 at 7:12
I would want to do this for a couple reasons. For example if I need to just save multiple values into one variable, or if I simply want a more code-efficient way of creating a single object. It feels weird to define an entire class just to create a single object with it, but maybe that's just my fault and something that shouldn't bother me? It just feels very unnatural having come from JavaScript, but maybe it's the way it should be done. — OOPS Studio
– OOPS Studio, Commented Jan 8, 2021 at 7:47
If creating classes bothers you, stay away from Java. :) It looks like what you're looking for is duck typing (being able to access properties of objects that are not declared within a proper type) and/or tuples (grouping multiple values in a single unit that has a generic type and a neat syntax). Java lacks both, if you don't consider using reflection or third-party / DIY tuple libraries. — Costi Ciudatu
– Costi Ciudatu, Commented Jan 8, 2021 at 8:52

daniu · Accepted Answer · 2021-01-08 08:47:20Z

4

You can't really think of it as an "object" in Java. JavaScript objects are unique implementations of HashTables. If you want similar functionality, you can use a Java HashMap or ConcurrentHashMap(HashTable), depending on your specific requirements.

// we only add String->Double, but since you want to add "any type",
// we declare Map<Object, Object>
HashMap<Object, Object> map= new HashMap<>(); 
map.put("Zara", new Double(3434.34));
map.put("Mahnaz", new Double(123.22));

String[] names = map.keys();
      
while(names.hasMoreElements()) {
    str = (String) names.nextElement();
    System.out.println(str + ": " + map.get(str));
}

edited Jan 8, 2021 at 8:47

daniu

15.1k7 gold badges37 silver badges63 bronze badges

answered Jan 8, 2021 at 7:10

Mick

7964 silver badges8 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

daniu Over a year ago

From the javadoc: "As of the Java 2 platform v1.2, this class was retrofitted to implement the Map interface, making it a member of the Java Collections Framework. Unlike the new collection implementations, Hashtable is synchronized. If a thread-safe implementation is not needed, it is recommended to use HashMap in place of Hashtable. If a thread-safe highly-concurrent implementation is desired, then it is recommended to use ConcurrentHashMap in place of Hashtable." - so, pretty much, never Hashtable.

EKW · Accepted Answer · 2021-01-08 07:16:11Z

1

So, all objects in java have a class associated with them. Even raw Objects have a class: The Object class! You won't be able to create an object without a class because all values need to have a type of some sort. But that's really not a huge problem. If you need an object that stores certain values, you can just create a class that has space for those values. There's really no situation where you would not be able to do this.

That being said, if you just want a way of mapping keys to values, I'd recommend looking into the Map data structure.

edited Jan 8, 2021 at 7:16

answered Jan 8, 2021 at 7:09

EKW

2,15315 silver badges24 bronze badges

Comments

Daniel · Accepted Answer · 2021-01-08 08:35:50Z

JavaScript classes are different from Java classes, JavaScript is not a class-based object-oriented language, an object in JS is used as a template to hold properties, but in Java classes could hold variables (properties) and functions, so to initialize an object in Java there has to be a class for that object, you can think of it as a blueprint of how the object will be initiated for example to create a class:

public class Example {
    public String link = "https://stackoverflow.com/";

    public void printLink() {
        System.out.println(link); // Prints the string stored in link
    }

    public void openLink() {
        // Some code to open the link in the browser
    }
}

To initialize an object from the class you created call this in your main or somewhere where the code will run:

Example example = new Example();
example.printLink(); // Printed the link
example.openLink(); // Opened the link
example.link = "https://example-link.com/"; // Changed the link

Note that the Example class could be in a different file and the file name has to be the same as the class name, here it is (Example.java)

Anyway if you are looking for an equivelant for JavaScript classes HashMap or HashTable could be very close.

Collectives™ on Stack Overflow

What's the Java equivalent of defining a classless object in JavaScript?

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related