Question

I have a method with a parameter containing generics.

public static void readList(List<ModelObject> list)
{
    // more code
}

I want to pass an ArrayList of ModelObjectImplementations to this method.

ArrayList<ModelObjectImplementation> myList;
myList = ...

readList(myList); // gives compilation error

ModelObject is an interface that ModelObjectImplementation implements. How can I change the method declaration to allow this?

Answer 1

You can use wildcards, if you’re using Java version 1.5 and higher.

public static void readList(List<? extends ModelObject> list)

This solution is more generic, because it fits for all java.util.List interface implementations and subclasses/subinterfaces of ModelObject.
For more details go to wildcards tutorial