Strange ClassCastException

Question

This:

Timerange longest = Timerange.longest(breaks); if (longest.durationInHours() >= MIN_FREE_HOURS) return true;

is OK.

But this:

if (Timerange.longest(breaks).durationInHours() >= MIN_FREE_HOURS) return true;

gives:

java.lang.ClassCastException

Do you know why?!

For simplicity:

public static final <T extends Timerange> T longest(List<T> timeranges) { return timeranges.get(0); }

Breaks:

List<Duty> breaks = week.substract(weekDuties);

How about showing a complete example which exhibits the problem? In particular, the declaration of breaks is missing. — starblue
– starblue, Commented Mar 15, 2009 at 8:06
Does Duty.durationInHours differ from Timerange.durationInHours? — Alex B
– Alex B, Commented Jul 27, 2010 at 19:03

MarkusQ · Accepted Answer · 2009-03-14 23:10:28Z

1

What happens if you try:

if (((Timerange) Timerange.longest(breaks)).durationInHours() >= MIN_FREE_HOURS) return true;

e.g., cast it?

answered Mar 14, 2009 at 23:10

MarkusQ

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2 Comments

Etam Over a year ago

It is OK, but i need to know WHY? :).

MarkusQ Over a year ago

So from that we can conclude that longest isn't returning a Timerange, but something that's compatible with Timerange (otherwise the cast and the assignment would have failed). Why might that be?

Tom Hawtin - tackline · Accepted Answer · 2009-03-16 12:39:35Z

Presumably somewhere in your code you are getting a warning. Listen to your compiler.

To get details add -Xlint (in particular -Xlint:unchecked) to your javac commandline (or do your development environment's equivalent).

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