Is Null an Object

Is null an Object?

If null were an Object, it would support the methods of java.lang.Object such as equals(). However, this is not the case - any method invocation on a null results in a NullPointerException.

And this is what the Java Language Specification has to say on this topic:

There is also a special null type, the
type of the expression null, which has
no name. Because the null type has no
name, it is impossible to declare a
variable of the null type or to cast
to the null type. The null reference
is the only possible value of an
expression of null type. The null
reference can always be cast to any
reference type. In practice, the
programmer can ignore the null type
and just pretend that null is merely a
special literal that can be of any
reference type.

I think this can be boiled down to "null is special".

Why is null an object and what's the difference between null and undefined?

(name is undefined)

You: What is name?^(*)

JavaScript: name? What's a name? I don't know what you're talking about. You haven't ever mentioned any name before. Are you seeing some other scripting language on the (client-)side?

name = null;

You: What is name?

JavaScript: I don't know.

In short; undefined is where no notion of the thing exists; it has no type, and it's never been referenced before in that scope; null is where the thing is known to exist, but it's not known what the value is.

One thing to remember is that null is not, conceptually, the same as false or "" or such, even if they equate after type casting, i.e.

name = false;

You: What is name?

JavaScript: Boolean false.

name = '';

You: What is name?

JavaScript: Empty string

^{*: name in this context is meant as a variable which has never been defined. It could be any undefined variable, however, name is a property of just about any HTML form element. It goes way, way back and was instituted well before id. It is useful because ids must be unique but names do not have to be.}

Why is null not an object in Java, if it can be assigned to any reference type?

Unfortunately, in many tutorials, books and other resources about Java, the terms "object" and "variable" are used in a sloppy way, which can lead to confusion similar to what you describe in your question.

For example, look at this line of code:

String message = "Hello World";

People will often say "I have a String object named message here with the value "Hello World". This is wrong and it makes beginners think that objects and variables are the same thing, and that objects have names.

Accurate would be: "I have a variable named message here which is a reference to a String object with the value "Hello World".

Variables and objects are not the same thing. A variable* is not an object, it's a reference to an object (it's a pointer to an object somewhere in memory).

Variables have names. In the code above, there is a variable named message. Objects do not have names.

There is also not a one-to-one correspondence between variables and objects. Multiple variables may refer to the same object.

The value null is a special value that you can assign to variables* that means "this variable refers to no object". It's just like a null pointer in languages such as C and C++.

It doesn't really make sense to talk about null being an object. It's not an object, it's a special reference value to make variables refer to "no object".

If null can be assigned to any Object type

This is why I suspect you're confused about the difference between objects and variables: you do not assign null to an object, but to a variable (of "any object type" which is the same as "of a non-primitive type").

*: we're talking about variables of non-primitive types here

For a more advanced understanding:

The value null has a bit of a bad reputation (it's the cause of many bugs). You might want to use java.util.Optional to help prevent some of the problems that null causes.

See also the null object pattern, which is a design pattern about the idea of having a special object that represents "the empty value". This might be useful in special situations.

java.util.Objects.isNull vs object == null

should use object == null over Objects.isNull() in a if statement?

If you look at the source code of IsNull method,

 /* Returns true if the provided reference is null otherwise returns false.*/

 public static boolean isNull(Object obj) {
     return obj == null;
 }

It is the same. There is no difference. So you can use it safely.

Java - is `null` an instance of `object`?

No, it is a reference. null is not an object

String s = null;

System.out.println(s instanceof Object); // false

Is null an object in JavaScript?

Null is the absence of an object. Undefined means it hasn't been assigned yet, and null means it has been assigned to be nothing.

Null is not really a singleton object, because dereferencing it will cause an error; for (var x in null) will give you an error. Think back to the pointer days; null was the value a pointer had when it was not pointing to an object.

In Java, is null an existing object on the heap?

See here:

The Java IAQ:
Infrequently Answered Questions: Is null an Object?

What is the difference between null and undefined in JavaScript?

undefined means a variable has been declared but has not yet been assigned a value :

var testVar;
console.log(testVar); //shows undefined
console.log(typeof testVar); //shows undefined