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

Question

I read that null isn\'t an instanceof anything, but on the other hand that everything in Java extends Object class.

Answer 1

In a word, no.

Peter Norvig's Java IAQ addresses this question in some detail (specifically "Q: Is null an Object?")

Answer 2

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

String s = null;

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

Answer 3

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

Java Language Specification

Answer 4

No, null is not an object. It is a literal that means that a variable does not reference any object.

Answer 5

Hoping that this example clears your doubt :

public void printObject(Object object) {
    System.out.println("object referred");
}

public void printObject(double[] doubleArray) {
    System.out.println("Array of type double");
}

public static void main(String[] args) {
    JavaNullObjectTest javaNullObjectTest = new JavaNullObjectTest();

    javaNullObjectTest.printObject(null); //Array of type double

    javaNullObjectTest.printObject((Object)null); //object referred
}

We can but, convert a 'null' to object.

Answer 6

Null means that you don't have a reference to an object.

Object o = null;

o is a reference but there is no object referenced and no memory allocated for it.

o = new Object();

o is still a reference and holds the adress where the object is located in memory