Java中如何表示多对多的关系

public class Category
{
	private int id;
	private String name;
	private Set<Item> items;
}

public class Item
{
	private int id;
	private String name;
	private Set<Category> categories;
}

Category category = new Category();
category.setId(1);
category.setName("水果");
category.setItems(new HashSet<Item>());
category.getItems().add(new Item("苹果"));
category.getItems().add(new Item("西瓜"));