A boxed value is unboxed and then immediately reboxed

Question

I am getting the Findugs error "A boxed value is unboxed and then immediately reboxed".

This is the Code:

Employee emp = new Employee()
Long lmt = 123L;

emp.setLimit(Long.valueOf(lmt));

In this, Employee limit field is of type Long. Could you please let me know what is the error?

Is there a reason that you're using Long and not long variables and parameters? Since the limit parameter is a Long, why not simply pas `lmt` into the method? Why call `Long.valueOf(lmg)`? — Hovercraft Full Of Eels, Aug 22 '12 at 05:19

Peter Butkovic · Answer 1 · 2013-12-05T08:27:18.800

22

The problem is that you're converting Long -> long -> Long.

So in the background:

Long.valueOf(lmt) converts Long to long
emp.setLimit(<long>); converts long to Long again

As of Java 5 autoboxing happens => your code should look like this:

Employee emp = new Employee()
Long lmt = 123L;

emp.setLimit(lmt);

or even:

Employee emp = new Employee()
long lmt = 123L;

emp.setLimit(lmt);

edited Dec 05 '13 at 08:27

answered Aug 22 '12 at 05:23

Peter Butkovic

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score 4 · Answer 2 · answered Aug 22 '12 at 05:22

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That happens because Long.valueOf(long) will unbox your lmt from Long to long, just to get a Long again. As you said that limit is a Long, you don't need to use Long.valueOf, just use the var:

emp.setLimit(lmt);

answered Aug 22 '12 at 05:22

jpkroehling

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score 1 · Answer 3 · edited Aug 22 '12 at 05:31

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emp.setLimit(Long.valueOf(lmt));

Long.valueOf takes a long value, but you pass a Long value -- mandating unboxing. Immediately afterward, however, Long.valueOf re-boxes the value and the expression evaluates to a Long again. FindBugs detects the unnecessary conversion chain Long -> long -> Long.

edited Aug 22 '12 at 05:31

obataku

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answered Aug 22 '12 at 05:25

Andreas Dolk

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A boxed value is unboxed and then immediately reboxed

3 Answers3