Java Quiz of the Day

Patrick Jayet
May 19, 2010 · 1 min read

What gives

Double a = null;
Double b = a == null ? a : 1.0;

Response: as strange as it can seem at first look, b is not equal to null after the second statement, but the code produces a NullPointerException.

The reason for that is the type of the second expression (double) inside the ternery operator. The first expression ‘a’ of type Double is unboxed to double (calling doubleValue() on ‘a’ which is null), causing the NPE.

You can find a discussion about that here.

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Patrick Jayet

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Polyglot (FR, DE, EN, ES), polyglot programmer (Java, Groovy, Ruby, Swift, Objective-C, Scala, Python, O’Caml) polyglot methodologist (Scrum, Kanban, Lean).

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