Convert Callback into Java 8 Lambda expression

Question

In my current project, I'm working on a rather simple JavaFX GUI containing a TreeTableView. To initialize the View I have the following code.

cmdNrColumn.setCellFactory(new Callback<TreeTableColumn<Command, Command>, TreeTableCell<Command, Command>>() {
    @Override public TreeTableCell<Command, Command> call(final TreeTableColumn<Command, Command> p) {
        return new TreeTableCell<Command, Command>() {
            @Override protected void updateItem(Command item, boolean empty) {
                super.updateItem(item, empty);

                TreeTableView treeTable = p.getTreeTableView();

                if (getIndex() >= treeTable.getExpandedItemCount()) {
                    setText(null);
                } else {
                    TreeItem<Command> treeItem = treeTable.getTreeItem(getIndex());
                    if (item == null || empty || treeItem == null || treeItem.getValue() == null) {
                        setText(null);
                    } else {
                        setText(Integer.toString(item.getCmdNr()));
                    }
                }
            }
        };
    }
});

Being new to Java 8 I'm not quite sure if and how this could be simplified to a Lambda expression.

Any help or tutorial on how to convert complicated and nested calls to a Lambda expression would be kindly appreciated

Thanks!

Answer 1

You can transform the outer anonymous class into a lambda expression:

cmdNrColumn.setCellFactory(p ->
    new TreeTableCell<Command, Command>() {
        @Override
        protected void updateItem(Command item, boolean empty) {
            // ...
            TreeTableView treeTable = p.getTreeTableView();
            // ...
        }
    });

However, the same transformation isn't possible for the inner anonymous class, because TreeTableCell is an abstract class, and lambda expressions can only be used for interfaces.