Java filter list to generic type T

Question

How can I do the following (this doesn't compile):

<T> List<T> getElementsOf() {
    return list.stream()
            .filter(x -> x instanceof T)
            .map(x -> (T) x)
            .collect(toList());
}

What would be example of usage? Ideally, it should be like obj.<Derived>getElementsOf().

Answer 1

Although the other answer pretty much does the job, here's a better one:

<T> List<T> getElementsOf(Class<T> clazz) {
    return list.stream()
            .filter(clazz::isInstance)
            .map(clazz::cast)
            .collect(toList());
}

Notice that the clazz::isInstance thingy. Instead of comparing the two classes, it uses the isInstance method. According to the docs, this is equivalent to instanceof, which is what you wanted in the first place.

This method is the dynamic equivalent of the Java language instanceof operator.

Answer 2

I got the following:

<T> List<T> getChildrenOf(Class<T> clazz) {
    return children.stream()
            .filter(node -> node.getClass() == clazz)
            .map(node -> clazz.<T>cast(node))
            .collect(toList());
}

List<Mesh> nameNodes = b.getChildrenOf(Mesh.class);