Using legacy non-generic code from generic code

package com.Fooblibar.widgets;

public interface Part { ...}

public interface Assembly {
    Collection getParts(); // Returns a collection of Parts
}

public class Inventory {
    public static void addAssembly(String name, Collection parts) {...} // Adds an assembly into the DB
    public static Assembly getAssembly(String name) {...} // Looks up an assembly in the DB
}

package com.mycompany.inventory;

import com.Fooblibar.widgets.*;

public class Blade implements Part { ...  }

public class Guillotine implements Part { ... }

public class Main {
    public static void main(String[] args) {
        Collection<Part> c = new ArrayList<Part>();
        c.add(new Guillotine()) ;
        c.add(new Blade());
	Inventory.addAssembly("thingee", c);     // pass to "raw type"
	Collection<Part> k = Inventory.getAssembly("thingee").getParts();    // return from "raw type"
    }
}

• Collection
• Collection<Part>
• Collection<Object>
• Collection<?>

$ javac G25.java
Note: G25.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

$ java -Xlint:unchecked G25.java
G25.java:24: warning: [unchecked] unchecked conversion
found   : java.util.Collection
required: java.util.Collection
        Collection k = Inventory.getAssembly("thingee").getParts();    // return from "raw type"
                                                                      ^
1 warning