Here is a simplified version of a valid Java code (three files):

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public interface SomeInterface {
    void doSomething();
}
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public class ParentClass {
    public void doSomething() {}
}
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public class ChildClass extends ParentClass implements SomeInterface {}
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When I open SomeInterface, there is no icon "I" next to the method doSomething, it does not show that this method is implemented in ChildClass (inherited from SomeClass). The same problem is when I use alt+f7 and choose "Find Overriding Method" and "Include overloaded methods" - nothing is found.

When I could change the code to "class ParentClass implements SomeInterface" NetBeans would work fine. However, that would have unwanted consequences - there would be two classes implementing SomeInterface, which would confuse the dependency injection framework (and changing that would bring another issues).