How to implement a tree data-structure in Java?

Question

Is there any standard Java library class to represent a tree in Java?

Specifically I need to represent the following:

• The sub-tree at any node can have

Answer 1

In the past I have just used a nested map for this. This is what I use today, it is very simple but it fits my needs. Maybe this will help another one.

import com.fasterxml.jackson.annotation.JsonValue;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;

/**
 * Created by kic on 16.07.15.
 */
public class NestedMap {
    private final Map root = new HashMap<>();

    public NestedMap put(K key) {
        Object nested = root.get(key);

        if (nested == null || !(nested instanceof NestedMap)) root.put(key, nested = new NestedMap<>());
        return (NestedMap) nested;
    }

    public Map.Entry put(K key, V value) {
        root.put(key, value);

        return (Map.Entry) root.entrySet().stream().filter(e -> ((Map.Entry) e).getKey().equals(key)).findFirst().get();
    }

    public NestedMap get(K key) {
        return (NestedMap) root.get(key);
    }

    public V getValue(K key) {
        return (V) root.get(key);
    }

    @JsonValue
    public Map getRoot() {
        return root;
    }

    public static void main(String[] args) throws Exception {
        NestedMap test = new NestedMap<>();
        test.put("a").put("b").put("c", 12);
        Map.Entry foo = test.put("a").put("b").put("d", 12);
        test.put("b", 14);
        ObjectMapper mapper = new ObjectMapper();
        System.out.println(mapper.writeValueAsString(test));

        foo.setValue(99);
        System.out.println(mapper.writeValueAsString(test));

        System.out.println(test.get("a").get("b").getValue("d"));
    }
}