Strange NullPointerException in ternary conditional expression [duplicate]

问题

This question already has an answer here:

Strange Java behaviour. Ternary operator (1 answer)

Closed 5 years ago.

Can anyone tell me why does Java throw a NullPointerException here?

Float x = <some condition> ? myObject.getSomeFloat() : 0.0f;

• The method getSomeFloat returns Float.
• Changing 0.0f to new Float(0) works fine.

回答1:

The type of this ternary operator is float. Therefore, if myObject.getSomeFloat() returns null, a NullPointerException is thrown when <some condition> is true and myObject.getSomeFloat().floatValue() is called in order to convert the Float to float.

JLS 15.25:

If one of the second and third operands is of primitive type T, and the type of the other is the result of applying boxing conversion (§5.1.7) to T, then the type of the conditional expression is T.

In your case, you have a primitive type - float - and the Boxed version of that float - Float. Therefore, the type of the conditional expression is the primitive type - float.

来源：https://stackoverflow.com/questions/27730895/strange-nullpointerexception-in-ternary-conditional-expression