How to build an hierarchy tree of categories in java using enums or any other way?

Question

Assuming that we have a set of categories: categories={A,B}. Let\'s assume more that A consists of subcategories: {A1,A2,A3} and B consists of subcategories: {B1,B2}.In addi

Answer 1

java.util.Map objects with java.util.Collection value types can represent arbitrary tree structures:

    final Map> map = Collections.unmodifiableMap(
        new HashMap>() {
            {
                put(
                    "A",
                    Collections.unmodifiableSet(
                        new HashSet<>(Arrays.asList("A1", "A2", "A3"))
                    )
                );
                put(
                    "A1",
                    Collections.unmodifiableSet(
                        new HashSet<>(Arrays.asList("A1a", "A1b"))
                    )
                );
                put(
                    "A2",
                    Collections.unmodifiableSet(
                        new HashSet<>(Arrays.asList("A2a", "A2b"))
                    )
                );
                put(
                    "A3",
                    Collections.unmodifiableSet(
                        new HashSet<>(Arrays.asList("A3a", "A3b", "A3c"))
                    )
                );
                put(
                    "B",
                    Collections.unmodifiableSet(
                        new HashSet<>(Arrays.asList("B1", "B2"))
                    )
                );
                put(
                    "B1",
                    Collections.unmodifiableSet(
                        new HashSet<>(Arrays.asList("B1a", "B1b", "B1c"))
                    )
                );
                put(
                    "B2",
                    Collections.unmodifiableSet(
                        new HashSet<>(Arrays.asList("B2a", "B2b"))
                    )
                );
            }
        }
    );

Or you could try something like javax.swing.tree.DefaultTreeModel.