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I have a .jar which contains a class that I want to use: FooBar.class . This class is not in a package, its just sitting in the root directory of the .jar.

I've added the .jar to the project as a library, but the problem is, I don't know how to import it since its not in a package.

If I simply do: import FooBar; I get the error: . expected, and I'm not able to use FooBar class anywhere since it says Symbol not found.

Any ideas?

Ali
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2 Answers2

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You can't import from the default package. You (or whomever wrote it) shouldn't be using the default package anyway. You should avoid using the default package except for very small example programs.

If it's your code, put it in a package, as it should be. If it's someone else's, if they're taking the time to jar it up for you, they can put it in a package.

Alternatively, omit the import, but remember to add the jar to your classpath at compile time.

Alternatively, if you're lazy, and don't care about ignore all best practices (i.e. if this is a toy program, etc.)

$ jar -xvf <whatever>.jar

Will extract the files from the jar into the current directory, at which point you can use them as normal. If you're on Windows, you can probably do this via whatever program handles .zip files for you - a .jar is just a .zip with a manifest.

James
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I think you can do this with reflection.

Edit2:

Okay, perhaps you don't need reflection. I did another test where I instantiated Test directly and it worked. All you have to do is place the jar in your classpath, as the above poster said, without trying to import the class file.

Edit: Why the downvote? I was absolutely correct.

// No package statement here
public class Test {
  public String getMessage() {
    return "Hello World!";
  }
}

$ javac Test.java
$ jar cvf my.jar Test.class

// No import statements needed
public class TestRefl {
  public static void main(String[] args) throws Exception {
    Class c = Class.forName("Test");
    Test t = (Test) c.newInstance();
    System.out.println(t.getMessage());
  }
}

$ javac TestRefl.java
$ java -classpath ".:my.jar" TestRefl
$ Hello World!

You don't even have to import the class from the default package. And now you have an instance of it so you can do whatever you want.

ktm5124
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  • -1 for the insane advice to use reflection. Delete this scrap! – Ingo Mar 10 '13 at 02:04
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    Read: http://stackoverflow.com/questions/283816/how-to-access-java-classes-in-the-default-package. So, you might not be able to access the default package from a named package after all. There might be cases where it's not possible without reflection. – ktm5124 Mar 10 '13 at 02:17
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    +1 as I don't agree with down votes. Apparently, question is about how to hack something. As a result, a number of hacky solutions. Some of them don't always work, but give ideas on how to work around the issue. – ATrubka Mar 10 '13 at 03:12
  • Thank you ATrubka. Hope you are looking forward to the Windy City warming up :-) – ktm5124 Mar 10 '13 at 03:57
  • I see no possible way to do this with reflection. If you find it, add it to the answer and maybe the downvotes will go away. – ccleve Mar 10 '13 at 17:26
  • The above example works. The question is whether it's necessary. It's not necessary when you're using a class from the default package of another jar within the default package. However, it might be necessary if you're using a class from the default package of another jar within a named package. I know - it's very confusing! And probably not worth the time to figure out. – ktm5124 Mar 11 '13 at 02:28
  • Yes it works, but what when you want to extend class like that? ex: MyClass extends ClassWithoutPackage For me it's not working... – Matt Jul 13 '22 at 13:32