how to use class files inside a jar file?

Question

I'm using eclipse , the jar files locate in ~/zmx/alg4/algs4.jar, the class file I need is algs4.jar/A.class. my project exists in ~/workspace/test. the jar file are already in Referenced Libraries , how can I use the class file in my project? I've already tried:

import A; 
private A variable = new A();

but it doesn't work.

Answer 1

You can't use classes in the default package from a named package: "[import] require a compile-time error on any attempt to import a type in an unnamed package" . You may want to access it via reflection (see below), or repackage your library algs4.jar if you have the source code.

 Class.forName("SomeClass").getMethod("someMethod").invoke(null);