D5_Solar.java

package cosmos.solarsystem;
import cosmos.cygnus.*;

/**
 * Created by Wook on 2015-12-10.
 */
public class D5_Solar {
    public static void main(String[] args) {
        Sun sun = new Sun();
        Vega vega = new Vega();
        Denev denev = new Denev();

        System.out.println(sun.getName());
        System.out.println(vega.getName());
        System.out.println(denev.getName());
    }
}

class Sun {
    public String getName() {
        return "태양";
    }
}

Denev.java

package cosmos.cygnus;

/**
 * Created by Wook on 2015-12-10.
 */
public class Denev {
    public String getName() {
        return "데네브";
    }
}

Vega.java

package cosmos.cygnus;

/**
 * Created by Wook on 2015-12-10.
 */
public class Vega {
    public String getName() {
        return "베가";
    }
}

잘 하셨습니다.
채널에 좀 더 자세한 cosmos 예제가 있으니까 꼭 참조해보세요.