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<String,Set<String>> map = Collections.unmodifiableMap(
        new HashMap<String,Set<String>>() {
            {
                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.

Answer 2

Probably an implementation of this:

public interface Category {
    String getName();
    Category getParent();
    List<Category> getSiblings();
    List<Category> getChildren();
    List<Category> getDescendants();
    void addChild(Category category);
    void addChildren(List<Category> categories);
}

Answer 3

In addition to the answers above, I would like to share something I found on the internet too. I have not tested it yet, but it seems to offer an alternative:

http://alexradzin.blogspot.hk/2010/10/hierarchical-structures-with-java-enums_05.html

public enum OsType {
OS(null),
    Windows(OS),
        WindowsNT(Windows),
            WindowsNTWorkstation(WindowsNT),
            WindowsNTServer(WindowsNT),
        Windows2000(Windows),
            Windows2000Server(Windows2000),
            Windows2000Workstation(Windows2000),
        WindowsXp(Windows),
        WindowsVista(Windows),
        Windows7(Windows),
        Windows95(Windows),
        Windows98(Windows),
    Unix(OS) {
            @Override
            public boolean supportsXWindows() {
                return true;
            }
        },
        Linux(Unix),
        AIX(Unix),
        HpUx(Unix),
        SunOs(Unix),
;
private OsType parent = null;

private OsType(OsType parent) {
    this.parent = parent;
}