Example:

    sealed interface BinaryTree {
      record Leaf(int value) implements BinaryTree {}
      record Node(BinaryTree lhs,
                BinaryTree rhs,
                int value) implements BinaryTree {}
    }

    public class Hello {
      static int sum(BinaryTree tree) {
        return switch (tree) {
        case BinaryTree.Leaf(var value) -> value;
        case BinaryTree.Node(var lhs, var rhs, var value) -> sum(lhs) + value + sum(rhs);
        };
      }
    
      public static void main(String... args) {
        var tree = new BinaryTree.Node(
                                       new BinaryTree.Leaf(1),
                                       new BinaryTree.Node(
                                                           new BinaryTree.Leaf(2),
                                                           new BinaryTree.Leaf(3),
                                                           4),
                                       5);
        System.out.println(tree);
        System.out.println("Sum: " + sum(tree));
      }
    }

EDIT: I didn't handle the `null` case above... so it would be a NullPointerException if someone passed null... apparently, Java decided to make handling `null` optional. More information: https://www.baeldung.com/java-lts-21-new-features

    final boolean hasUncollectedSecret =
       switch (each)
       {
               
          case Wall()    -> false;
          case Goal()    -> false;
          case Player p  -> false;
          case BasicCell(Underneath(_, var collectible), _)
             ->
                switch (collectible)
                {
                        
                   case NONE, KEY -> false;
                   case SECRET -> true;
                        
                };
          case Lock()    -> false;
               
       };