Java – Is null check needed before calling instanceof

javanullnullpointerexception

Will null instanceof SomeClass return false or throw a NullPointerException?

Best Answer

No, a null check is not needed before using instanceof.

The expression x instanceof SomeClass is false if x is null.

The Java 11 Language Specification expresses this concisely in section 15.20.2, "Type comparison operator instanceof". (Java 17 expresses this less concisely, after the introduction of instanceof patternmatching.)

"At run time, the result of the instanceof operator is true if the value of the RelationalExpression is not null and the reference could be cast to the ReferenceType without raising a ClassCastException. Otherwise the result is false."

So if the operand is null, the result is false.

Related Solutions

Javascript – How to check for an empty/undefined/null string in JavaScript

If you just want to check whether there's a truthy value, you can do:

if (strValue) {
    //do something
}

If you need to check specifically for an empty string over null, I would think checking against "" is your best bet, using the === operator (so that you know that it is, in fact, a string you're comparing against).

if (strValue === "") {
    //...
}

Sql-server – Altering a column: null to not null

First, make all current NULL values disappear:

UPDATE [Table] SET [Column]=0 WHERE [Column] IS NULL

Then, update the table definition to disallow "NULLs":

ALTER TABLE [Table] ALTER COLUMN [Column] INTEGER NOT NULL

Best Answer

Related Solutions

Javascript – How to check for an empty/undefined/null string in JavaScript

Sql-server – Altering a column: null to not null

Related Topic