Ensuring type safety, honoring supertype contract

If I can't do instanceof T in Java (due to type erasure), then how do I write a generic tree node? setUserObject() accepts Object, not T. Do I have no better choice than making clients pass Class literals? public class ItemTreeNode extends DefaultMutableTreeNode { public ItemTreeNode(T userObject) { super(userObject); } @Override @SuppressWarnings("unchecked") public void setUserObject(Object userObject) { super.setUserObject((T) userObject); // would throw ClassCastException if it's not T } @Override @SuppressWarnings("unchecked") public T getUserObject() { return (T) super.getUserObject(); } }

Mar 12, 2025 - 16:15

If I can't do instanceof T in Java (due to type erasure), then how do I write a generic tree node? setUserObject() accepts Object, not T. Do I have no better choice than making clients pass Class literals?

public class ItemTreeNode extends DefaultMutableTreeNode {

    public ItemTreeNode(T userObject) {
        super(userObject);
    }

    @Override
    @SuppressWarnings("unchecked")
    public void setUserObject(Object userObject) {
        super.setUserObject((T) userObject); // would throw ClassCastException if it's not T
    }

    @Override
    @SuppressWarnings("unchecked")
    public T getUserObject() {
        return (T) super.getUserObject();
    }
}