Problem in compiling java project in Netbeans

I have a problem now : When I want to compile my project in Netbeans IDE I had this message error :

Problem: The project uses a class library called "toplink", but this class library was not found.
So开发者_如何学JAVAlution: Click Resolve to open the Library Manager and create a new class library called "toplink".

In fact I didn't change anything and it works fine before?

What's the problem?

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It seems that you have to import the library itself.

On the left pane in your Netbeans editor, you should have a series of panes. One of these is called the Projects pane. If you click on it, you should be able to see the files and packages which make up the project you are editing as nodes. One of these nodes, at the very end is called "Libraries". Right click on this node and select "Add Library". From there, you should be able to browse and locate the library.

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I believe libraries are defined for the NetBeans installation rather than for the project. You can import a library into a project which would make it available on other NetBeans installations. Perhaps you are on a different computer or a new installation of NetBeans?