Null Literal

A literal (textual) expression of the null value in source code.

The null literal is used to denote the special null value, which cast to any reference type. There is only one null value whose type is the null type. The null type cannot be expressed in Java code.

Syntax

The Null Literal has one form:

1

null

Syntax Elements

1 The null literal. Parsed as a single token.

Usage

The null value is a special type of value that's used to represent the lack of information. The null literal is used to explicitly write the null value in source code:

String x = null;

The null value is assignable to any reference type, including variables of any type parameter, even if the type is not visible (see note 1).

Examples

Method Invocation

Invoking a method on the null value results in a java.lang.NullPointerException. Doing so requires that the null value be cast to some reference type, such as String:

int x = ((String) null).length(); // throws a NullPointerException

or more simply:

((String) null).length(); // throws a NullPointerException

Throwing null

The null literal can be the operand of the throw operator in a throw statement:

throw null;

This creates and throws a java.lang.NullPointerException.

Notes

1. The null literal can be used to call a function that has parameters of inaccessible type. For example:

   class A {
   	private static class Hidden {
   
   	}
   
   	public static void secureMethod(Hidden hidden) {
   
   	}
   }
   
   class B {
   	public static void test() {
   		// Call A.secureMethod(A.Hidden) without having an instance of the class, A.Hidden
   		A.secureMethod(null); // null is assignable to A.Hidden, so no instance of A.Hidden needed
   		// A.secureMethod(new A.Hidden()); // Not allowed; A.Hidden is private
   	}
   }