public interface SomeInterface {
}
public class SomeClass implements SomeInterface{
}

import java.io.ObjectInputStream.GetField;
import java.util.Vector;

public class Main {
	public static void main(String[] args) {
		SomeInterface[] interfaces = getSomeClassesObjects(); // That's correct
		Vector<SomeInterface> interfaces1 = getSomeClassesObjects1(); // "type mismatch: Cannot convert ... " error
		Vector<SomeInterface> interfaces2 = getSomeClassesObjects2(); // "type mismatch: Cannot convert ... " error
	}
	
	private static SomeClass[] getSomeClassesObjects() {
		return null;
	}
	
	private static Vector<SomeClass> getSomeClassesObjects1() {
		return null;
	}
	
	private static Vector<? extends SomeInterface> getSomeClassesObjects2() {
		return null;
	}
}