Can someone explain me what null keyword does?

Question

I serched for information on google but didn't find any good explanation.

Answer 1

What language?

In SQL, for instance, it's a flag to tell that a field has no value.
In C and C++, the NULL macro is equivalent to 0.

Answer 2

You can test it out for yourself:

class Test {}

public class Program
{
public static void main(String[] args) {
Test one = null;
Test two = new Test();

System.out.println(one);
System.out.println(two);
}
}

Answer 3

For C# and Java, null refers to a null reference, the default value of all reference type. Objects which are null, cannot be used to invoke class methods (exceptions will be thrown).

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/null
https://stackoverflow.com/questions/2707322/what-is-null-in-java

Quoting Roman Cherepanov in the above article

- "null is used to denote non-existence of an object".

Answer 4

C# / Java

Answer 5

Good explanation! Thanks alot!

Answer 6

Another way to see it would be that NULL is a value that indicates the variable has no useful value assigned yet.
You can see it similar to \0, which indicates the end of a string in C and C++, or ony othe control character, which are also values that indicate things