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Queue interface

Joanna Spence

Joined: May 31, 2010
Posts: 23
In a java example it shows you can implement a Queue with:

Queue queue= new Queue();

However, I receive an error stating it's abtract and cannot be instantiated...how do I work with this abstract class?

Rob Spoor

Joined: Oct 27, 2005
Posts: 20132

Find a non-abstract class that implements the Queue interface, then use it on the right hand side.

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Ernest Friedman-Hill
author and iconoclast

Joined: Jul 08, 2003
Posts: 24193

Hi Joanna,

Maybe the example is old(ish) was referring to a Queue class written before the Java API contained such an interface? Another giveaway that this might be old is that the modern Queue interface takes a type parameter, which isn't in your example.

To work with a Queue nowadays, anyway, you'd need to create an instance of some class that implements Queue, like LinkedList. So

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Joanna Spence

Joined: May 31, 2010
Posts: 23
Ooooooh...okay I will try that...
Joanna Spence

Joined: May 31, 2010
Posts: 23
Ok...it compiled, but it states to compile with -Xlint because it's marked for unchecked or unsafe operations..
Jelle Klap

Joined: Mar 10, 2008
Posts: 1932

That's down to Generics, or rather lack thereof. Have a look at this tutorial if you would like to know more about that subject. For now though, realize that it's a warning, not an error, and you could ignore it if you so choose. The -Xlint suggestion you can safely ignore for now. This javac option will enable all compiler warnings. If you want to know more about javac and its options, have a look here.

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subject: Queue interface
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