Question

Is it possible to create the below function into a generic function that I can re-use?

I want to pass in a collection, and return a list of a particular property in the object.

So far example I have this:

   private List<Integer> getPropertyABCIdsFromSomeObject(List<SomeObject> someObjects) {
        List<Integer> ids = new ArrayList<Integer>();
        for(SomeObject so : someObjects) {
            ids.add(so.getPropertyABCId());
        }
        return ids;
    }

So this method works only for type SomeObject, and returns a list of PropertyABCId.

Now if I want a list of some other property, I have to replicate this function with very little that changes.

Can generics save the day here?

Answer 1

You would need an interface, but yes:

interface HasProperty<T> {
    T getProperty();
}

public static <T> List<T> getProperties(List<? extends HasProperty<T>> items) {
    List<T> properties = new ArrayList<T>();
    for (HasProperty<T> item : items) {
        properties.add(item.getProperty());
    }
    return properties;
}