Generate Tree Structure from Arrays Java

Question

I have an ArrayList of String arrays in java named:

List<String[]> initialList = new ArrayList<String[]>();

This contains the following data (This is a snippet of it, it actually includes about 900 rows that go on to include Charlie, Delta, Echo, each with the same structure as these:

[Alpha, A1, 1, null]
[Alpha, A1, 2, null]
[Alpha, A1, 3, null]
[Alpha, A1, 4, null]
[Alpha, A1, 5, null]
[Alpha, A1, 6, null]
[Alpha, A1, 7, null]
[Alpha, A1, 8, null]
[Alpha, A1, 9, null]
[Alpha, A1, 10, null]
[Alpha, A1, 11, null]
[Alpha, A1, 12, null]
[Alpha, A1, 13, null]
[Alpha, A1, 14, null]
[Alpha, A1, 15, null]
[Alpha, A1, 16, null]
[Alpha, A1, 17, null]
[Alpha, A1, 18, null]
[Alpha, A1, 19, null]
[Alpha, A1, 20, null]
[Alpha, A1, 21, null]
[Alpha, A1, 22, null]
[Alpha, A1, 23, null]
[Alpha, A1, 24, null]
[Alpha, A1, 25, null]
[Alpha, A1, 26, null]
[Alpha, A1, 27, null]
[Alpha, A1, 28, null]
[Alpha, A1, 29, null]
[Alpha, A1, 30, null]
[Alpha, A1, 31, null]
[Alpha, A1, 32, null]
[Alpha, A1, 33, null]
[Alpha, A1, 34, null]
[Alpha, A1, 35, null]
[Alpha, A1, 36, null]
[Alpha, A1, 37, null]
[Alpha, A1, 38, null]
[Alpha, A1, 39, null]
[Alpha, A1, 40, null]
[Alpha, A1, 41, null]
[Alpha, A1, 42, null]
[Alpha, A1, 43, null]
[Alpha, A1, 44, null]
[Alpha, A1, 45, null]
[Alpha, A1, 46, null]
[Alpha, A1, 47, null]
[Alpha, A1, 48, null]
[Alpha, A1, 49, null]
[Alpha, A1, 50, null]
[Alpha, A1, 51, null]
[Alpha, A1, 52, null]
[Alpha, A1, 53, null]
[Alpha, A1, 54, null]
[Alpha, A2, 1, null]
[Alpha, A2, 2, null]
[Alpha, A2, 3, null]
[Alpha, A2, 4, null]
[Alpha, A2, 5, null]
[Alpha, A2, 6, null]
[Alpha, A2, 7, null]
[Alpha, A2, 8, null]
[Alpha, A2, 9, null]
[Alpha, A2, 10, null]
[Alpha, A2, 11, null]
[Alpha, A2, 12, null]
[Alpha, A2, 13, null]
[Alpha, A2, 14, null]
[Alpha, A2, 15, null]
[Alpha, A2, 16, null]
[Alpha, A2, 17, null]
[Alpha, A2, 18, null]
[Alpha, A2, 19, null]
[Alpha, A2, 20, null]
[Alpha, A2, 21, null]
[Alpha, A2, 22, null]
[Alpha, A2, 23, null]
[Alpha, A2, 24, null]
[Alpha, A2, 25, null]
[Alpha, A2, 26, null]
[Alpha, A2, 27, null]
[Alpha, A2, 28, null]
[Alpha, A2, 29, null]
[Alpha, A2, 30, null]
[Alpha, A2, 31, null]
[Alpha, A2, 32, null]
[Alpha, A2, 33, null]
[Alpha, A2, 34, null]
[Alpha, A2, 35, null]
[Alpha, A2, 36, null]
[Alpha, A2, 37, null]
[Alpha, A2, 38, null]
[Alpha, A2, 39, null]
[Alpha, A2, 40, null]
[Alpha, A2, 41, null]
[Alpha, A2, 42, null]
[Alpha, A2, 43, null]
[Alpha, A2, 44, null]
[Alpha, A2, 45, null]
[Alpha, A2, 46, null]
[Alpha, A2, 47, null]
[Alpha, A2, 48, null]
[Alpha, A2, 49, null]
[Alpha, A2, 50, null]
[Alpha, A2, 51, null]
[Alpha, A2, 52, null]
[Alpha, A2, 53, null]
[Alpha, A2, 54, null]
[Alpha, A3, 1, null]
[Alpha, A3, 2, null]
[Alpha, A3, 3, null]
[Alpha, A3, 4, null]
[Alpha, A3, 5, null]
[Alpha, A3, 6, null]
[Alpha, A3, 7, null]
[Alpha, A3, 8, null]
[Alpha, A3, 9, null]
[Alpha, A3, 10, null]
[Alpha, A3, 11, null]
[Alpha, A3, 12, null]
[Alpha, A3, 13, null]
[Alpha, A3, 14, null]
[Alpha, A3, 15, null]
[Alpha, A3, 16, null]
[Alpha, A3, 17, null]
[Alpha, A3, 18, null]
[Alpha, A3, 19, null]
[Alpha, A3, 20, null]
[Alpha, A3, 21, null]
[Alpha, A3, 22, null]
[Alpha, A3, 23, null]
[Alpha, A3, 24, null]
[Alpha, A3, 25, null]
[Alpha, A3, 26, null]
[Alpha, A3, 27, null]
[Alpha, A3, 28, null]
[Alpha, A3, 29, null]
[Alpha, A3, 30, null]
[Alpha, A3, 31, null]
[Alpha, A3, 32, null]
[Alpha, A3, 33, null]
[Alpha, A3, 34, null]
[Alpha, A3, 35, null]
[Alpha, A3, 36, null]
[Alpha, A3, 37, null]
[Alpha, A3, 38, null]
[Alpha, A3, 39, null]
[Alpha, A3, 40, null]
[Alpha, A3, 41, null]
[Alpha, A3, 42, null]
[Alpha, A3, 43, null]
[Alpha, A3, 44, null]
[Alpha, A3, 45, null]
[Alpha, A3, 46, null]
[Alpha, A3, 47, null]
[Alpha, A3, 48, null]
[Alpha, A3, 49, null]
[Alpha, A3, 50, null]
[Alpha, A3, 51, null]
[Alpha, A3, 52, null]
[Alpha, A3, 53, null]
[Alpha, A3, 54, null]
[Alpha, A3, 55, null]
[Alpha, A3, 56, null]
[Alpha, A3, 57, null]
[Alpha, A3, 58, null]
[Alpha, A3, 59, null]
[Alpha, A3, 60, null]
[Alpha, A4, 1, null]
[Alpha, A4, 2, null]
[Alpha, A4, 3, null]
[Alpha, A4, 4, null]
[Alpha, A4, 5, null]
[Alpha, A4, 6, null]
[Alpha, A4, 7, null]
[Alpha, A4, 8, null]
[Alpha, A4, 9, null]
[Alpha, A4, 10, null]
[Alpha, A4, 11, null]
[Alpha, A4, 12, null]
[Alpha, A4, 13, null]
[Alpha, A4, 14, null]
[Alpha, A4, 15, null]
[Alpha, A4, 16, null]
[Alpha, A4, 17, null]
[Alpha, A4, 18, null]
[Alpha, A4, 19, null]
[Alpha, A4, 20, null]
[Alpha, A4, 21, null]
[Alpha, A4, 22, null]
[Alpha, A4, 23, null]
[Alpha, A4, 24, null]
[Alpha, A4, 25, null]
[Alpha, A4, 26, null]
[Alpha, A4, 27, null]
[Alpha, A4, 28, null]
[Alpha, A4, 29, null]
[Alpha, A4, 30, null]
[Alpha, A4, 31, null]
[Alpha, A4, 32, null]
[Alpha, A4, 33, null]
[Alpha, A4, 34, null]
[Alpha, A4, 35, null]
[Alpha, A4, 36, null]
[Alpha, A4, 37, null]
[Alpha, A4, 38, null]
[Alpha, A4, 39, null]
[Alpha, A4, 40, null]
[Alpha, A4, 41, null]
[Alpha, A4, 42, null]
[Alpha, A4, 43, null]
[Alpha, A4, 44, null]
[Alpha, A4, 45, null]
[Alpha, A4, 46, null]
[Alpha, A4, 47, null]
[Alpha, A4, 48, null]
[Alpha, A4, 49, null]
[Alpha, A4, 50, null]
[Alpha, A4, 51, null]
[Alpha, A4, 52, null]
[Alpha, A4, 53, null]
[Alpha, A4, 54, null]
[Alpha, A4, 55, null]
[Alpha, A4, 56, null]
[Alpha, A4, 57, null]
[Alpha, A4, 58, null]
[Alpha, A4, 59, null]
[Alpha, A4, 60, null]
[Bravo, B1, 1, null]
[Bravo, B1, 2, null]
[Bravo, B1, 3, null]
[Bravo, B1, 4, null]
[Bravo, B1, 5, null]
[Bravo, B1, 6, null]
[Bravo, B1, 7, null]
[Bravo, B1, 8, null]
[Bravo, B1, 9, null]
[Bravo, B1, 10, null]
[Bravo, B1, 11, null]
[Bravo, B1, 12, null]
[Bravo, B1, 13, null]
[Bravo, B1, 14, null]
[Bravo, B1, 15, null]
[Bravo, B1, 16, null]
[Bravo, B1, 17, null]
[Bravo, B1, 18, null]
[Bravo, B1, 19, null]
[Bravo, B1, 20, null]
[Bravo, B1, 21, null]
[Bravo, B1, 22, null]
[Bravo, B1, 23, null]
[Bravo, B1, 24, null]
[Bravo, B1, 25, null]
[Bravo, B1, 26, null]
[Bravo, B1, 27, null]
[Bravo, B1, 28, null]
[Bravo, B1, 29, null]
[Bravo, B1, 30, null]
[Bravo, B1, 31, null]
[Bravo, B1, 32, null]
[Bravo, B1, 33, null]
[Bravo, B1, 34, null]
[Bravo, B1, 35, null]
[Bravo, B1, 36, null]
[Bravo, B1, 37, null]
[Bravo, B1, 38, null]
[Bravo, B1, 39, null]
[Bravo, B1, 40, null]
[Bravo, B1, 41, null]
[Bravo, B1, 42, null]
[Bravo, B1, 43, null]
[Bravo, B1, 44, null]
[Bravo, B1, 45, null]
[Bravo, B1, 46, null]
[Bravo, B1, 47, null]
[Bravo, B1, 48, null]
[Bravo, B1, 49, null]
[Bravo, B1, 50, null]
[Bravo, B1, 51, null]
[Bravo, B1, 52, null]
[Bravo, B1, 53, null]
[Bravo, B1, 54, null]
[Bravo, B1, 55, null]
[Bravo, B1, 56, null]
[Bravo, B1, 57, null]
[Bravo, B1, 58, null]
[Bravo, B1, 59, null]
[Bravo, B1, 60, null]
[Bravo, B2, 1, null]
[Bravo, B2, 2, null]
[Bravo, B2, 3, null]
[Bravo, B2, 4, null]
[Bravo, B2, 5, null]
[Bravo, B2, 6, null]
[Bravo, B2, 7, null]
[Bravo, B2, 8, null]
[Bravo, B2, 9, null]
[Bravo, B2, 10, null]
[Bravo, B2, 11, null]
[Bravo, B2, 12, null]
[Bravo, B2, 13, null]
[Bravo, B2, 14, null]
[Bravo, B2, 15, null]
[Bravo, B2, 16, null]
[Bravo, B2, 17, null]
[Bravo, B2, 18, null]
[Bravo, B2, 19, null]
[Bravo, B2, 20, null]
[Bravo, B2, 21, null]
[Bravo, B2, 22, null]
[Bravo, B2, 23, null]
[Bravo, B2, 24, null]
[Bravo, B2, 25, null]
[Bravo, B2, 26, null]
[Bravo, B2, 27, null]
[Bravo, B2, 28, null]
[Bravo, B2, 29, null]
[Bravo, B2, 30, null]
[Bravo, B2, 31, null]
[Bravo, B2, 32, null]
[Bravo, B2, 33, null]
[Bravo, B2, 34, null]
[Bravo, B2, 35, null]
[Bravo, B2, 36, null]
[Bravo, B2, 37, null]
[Bravo, B2, 38, null]
[Bravo, B2, 39, null]
[Bravo, B2, 40, null]
[Bravo, B2, 41, null]
[Bravo, B2, 42, null]
[Bravo, B2, 43, null]
[Bravo, B2, 44, null]
[Bravo, B2, 45, null]
[Bravo, B2, 46, null]
[Bravo, B2, 47, null]
[Bravo, B2, 48, null]
[Bravo, B2, 49, null]
[Bravo, B2, 50, null]
[Bravo, B2, 51, null]
[Bravo, B2, 52, null]
[Bravo, B2, 53, null]
[Bravo, B2, 54, null]
[Bravo, B2, 55, null]
[Bravo, B2, 56, null]
[Bravo, B2, 57, null]
[Bravo, B2, 58, null]
[Bravo, B2, 59, null]
[Bravo, B2, 60, null]
[Bravo, B3, 1, null]
[Bravo, B3, 2, null]
[Bravo, B3, 3, null]
[Bravo, B3, 4, null]
[Bravo, B3, 5, null]
[Bravo, B3, 6, null]
[Bravo, B3, 7, null]
[Bravo, B3, 8, null]
[Bravo, B3, 9, null]
[Bravo, B3, 10, null]
[Bravo, B3, 11, null]
[Bravo, B3, 12, null]
[Bravo, B3, 13, null]
[Bravo, B3, 14, null]
[Bravo, B3, 15, null]
[Bravo, B3, 16, null]
[Bravo, B3, 17, null]
[Bravo, B3, 18, null]
[Bravo, B3, 19, null]
[Bravo, B3, 20, null]
[Bravo, B3, 21, null]
[Bravo, B3, 22, null]
[Bravo, B3, 23, null]
[Bravo, B3, 24, null]
[Bravo, B3, 25, null]
[Bravo, B3, 26, null]
[Bravo, B3, 27, null]
[Bravo, B3, 28, null]
[Bravo, B3, 29, null]
[Bravo, B3, 30, null]
[Bravo, B3, 31, null]
[Bravo, B3, 32, null]
[Bravo, B3, 33, null]
[Bravo, B3, 34, null]
[Bravo, B3, 35, null]
[Bravo, B3, 36, null]
[Bravo, B3, 37, null]
[Bravo, B3, 38, null]
[Bravo, B3, 39, null]
[Bravo, B3, 40, null]
[Bravo, B3, 41, null]
[Bravo, B3, 42, null]
[Bravo, B3, 43, null]
[Bravo, B3, 44, null]
[Bravo, B3, 45, null]
[Bravo, B3, 46, null]
[Bravo, B3, 47, null]
[Bravo, B3, 48, null]
[Bravo, B3, 49, null]
[Bravo, B3, 50, null]
[Bravo, B3, 51, null]
[Bravo, B3, 52, null]
[Bravo, B3, 53, null]

The structure is as follows: Alpha, Bravo, Charlie, Delta, and Echo are root nodes that hold: (A1, A2, A3, A4) (B1, B2, B3, B4) (C1, C2, C3, C4) ect... which then each hold a 'n' number of spots where each number holds a persons name.

I need to make this into a Hierarchical Tree Structure. I have tried the following:

Map<String, Set<String>> myNodes = new LinkedHashMap<String, Set<String>>();

    for(String[] myArray : initialList) {
       String previousNode = null;
       for(String node : myArray) {
          if(myNodes.get(node) == null) {
             myNodes.put(node, new HashSet<String>());
          }


          if(previousNode != null) {
             myNodes.get(previousNode).add(node);
          }

          previousNode = node;

       }
    }

But this outputs as follows, which as you can see is wrong and not what I am looking for (again, just a snippet of the full output).

Alpha : [A2, A1, A4, A3]
A1 : [35, 36, 33, 34, 39, 37, 38, 43, 42, 41, 40, 22, 23, 24, 25, 26, 27, 28, 29, 3, 2, 1, 7, 30, 6, 5, 32, 4, 31, 9, 8, 19, 17, 18, 15, 16, 13, 14, 11, 12, 21, 20, 49, 48, 45, 44, 47, 46, 10, 51, 52, 53, 54, 50]
1 : [null]
null : []
2 : [null]
null : []
3 : [null]
4 : [null]
5 : [null]
6 : [null]
7 : [null]
8 : [null]
9 : [null]
10 : [null]
11 : [null]
12 : [null]
13 : [null]
14 : [null]
15 : [null]
16 : [null]
17 : [null]
18 : [null]
19 : [null]
20 : [null]
21 : [null]
22 : [null]
23 : [null]
24 : [null]
25 : [null]
26 : [null]
27 : [null]
28 : [null]
29 : [null]
30 : [null]
31 : [null]
32 : [null]
33 : [null]
34 : [null]
35 : [null]
36 : [null]
37 : [null]
38 : [null]
39 : [null]
40 : [null]
41 : [null]
42 : [null]
43 : [null]
44 : [null]
45 : [null]
46 : [null]
47 : [null]
48 : [null]
49 : [null]
50 : [null]
51 : [null]
52 : [null]
53 : [null]
54 : [null]
A2 : [35, 36, 33, 34, 39, 37, 38, 43, 42, 41, 40, 22, 23, 24, 25, 26, 27, 28, 29, 3, 2, 1, 7, 30, 6, 5, 32, 4, 31, 9, 8, 19, 17, 18, 15, 16, 13, 14, 11, 12, 21, 20, 49, 48, 45, 44, 47, 46, 10, 51, 52, 53, 54, 50]
A3 : [35, 36, 33, 34, 39, 37, 38, 43, 42, 41, 40, 22, 23, 24, 25, 26, 27, 28, 29, 3, 2, 1, 7, 30, 6, 5, 32, 4, 31, 9, 8, 59, 58, 57, 56, 19, 55, 17, 18, 15, 16, 13, 14, 11, 12, 21, 20, 60, 49, 48, 45, 44, 47, 46, 10, 51, 52, 53, 54, 50]
55 : [null]
56 : [null]
57 : [null]
58 : [null]
59 : [null]
60 : [null]
A4 : [35, 36, 33, 34, 39, 37, 38, 43, 42, 41, 40, 22, 23, 24, 25, 26, 27, 28, 29, 3, 2, 1, 7, 30, 6, 5, 32, 4, 31, 9, 8, 59, 58, 57, 56, 19, 55, 17, 18, 15, 16, 13, 14, 11, 12, 21, 20, 60, 49, 48, 45, 44, 47, 46, 10, 51, 52, 53, 54, 50]
Bravo : [B4, B3, B2, B1]
B1 : [35, 36, 33, 34, 39, 37, 38, 43, 42, 41, 40, 22, 23, 24, 25, 26, 27, 28, 29, 3, 2, 1, 7, 30, 6, 5, 32, 4, 31, 9, 8, 59, 58, 57, 56, 19, 55, 17, 18, 15, 16, 13, 14, 11, 12, 21, 20, 60, 49, 48, 45, 44, 47, 46, 10, 51, 52, 53, 54, 50]
B2 : [35, 36, 33, 34, 39, 37, 38, 43, 42, 41, 40, 22, 23, 24, 25, 26, 27, 28, 29, 3, 2, 1, 7, 30, 6, 5, 32, 4, 31, 9, 8, 59, 58, 57, 56, 19, 55, 17, 18, 15, 16, 13, 14, 11, 12, 21, 20, 60, 49, 48, 45, 44, 47, 46, 10, 51, 52, 53, 54, 50]
B3 : [35, 36, 33, 34, 39, 37, 38, 43, 42, 41, 40, 22, 23, 24, 25, 26, 27, 28, 29, 3, 2, 1, 7, 30, 6, 5, 32, 4, 31, 9, 8, 59, 58, 57, 56, 19, 55, 17, 18, 15, 16, 13, 14, 11, 12, 21, 20, 60, 49, 48, 45, 44, 47, 46, 10, 51, 52, 53, 54, 50]
B4 : [35, 36, 33, 34, 39, 37, 38, 43, 42, 41, 40, 22, 23, 24, 25, 26, 27, 28, 29, 3, 2, 1, 7, 30, 6, 5, 32, 4, 31, 9, 8, 59, 58, 57, 56, 19, 55, 17, 18, 15, 16, 13, 14, 11, 12, 21, 20, 60, 49, 48, 45, 44, 47, 46, 10, 51, 52, 53, 54, 50]

This was using a Map and LinkedHashMap, so I also tried it with a TreeMap (not even sure if this is what I need though):

TreeMap<String, Set<String>> myNodes = new TreeMap<String, Set<String>>();

    for(String[] myArray : initialList) {
       String previousNode = null;
       for(String node : myArray) {
          if(myNodes.get(node) == null) {
             myNodes.put(node, new HashSet<String>());
          }


          if(previousNode != null) {
             myNodes.get(previousNode).add(node);
          }

          previousNode = node;

       }
    }

But got the following error:

Exception in thread "main" java.lang.NullPointerException
    at java.util.TreeMap.getEntry(TreeMap.java:324)
    at java.util.TreeMap.get(TreeMap.java:255)

I need it hierarchical as I described above. I would love to describe exactly what it should output, but truthfully, I am not sure, I just know it needs to have a heirarchy structure and converted to JSON as described below.

Also, this must be converted to JSON in the following format so please keep that in mind (again, actual output is much larger, this is simply a structure example:

{
 "name":"Alpha",
 "children":[
   {
     "name":"A1",
     "children":[
        {
           "name":"1",
           "children":[
              {
                 "name":"null",
              },
            ]
           "name":"2",
           "children":[
              {
                 "name":"null",
              },
            ]
           "name":"3",
           "children":[
              {
                 "name":"null",
              },
            ]
        },
     "name":"A2",
     "children":[
        {
           "name":"1",
           "children":[
              {
                 "name":"null",
              },
            ]
           "name":"2",
           "children":[
              {
                 "name":"null",
              },
            ]
           "name":"3",
           "children":[
              {
                 "name":"null",
              },
            ]
        },
    ]   
},

I would appreciate any help I can get because I am truly stumped. Thanks!

Anshuman · Accepted Answer · 2015-03-11T04:32:41.227

Try running the following code.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;


class JsonModel {
    private String name;
    private List<JsonModel> children;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public List<JsonModel> getChildren() {
        return children;
    }
    public void setChildren(List<JsonModel> children) {
        this.children = children;
    }
    public String toString(){
        return "name: "+name + ", children: {"+children+"}";
    }
}

public class Test{

    public static void main(String a[])
    {
        ArrayList<String[]> initialList= new ArrayList<String[]>();
        initialList.add(new String[]{"Alpha", "A1", "1", null});
        initialList.add(new String[]{"Alpha", "A1", "2", null});
        initialList.add(new String[]{"Alpha", "A2", "1", null});
        initialList.add(new String[]{"Alpha", "A2", "2", null});
        initialList.add(new String[]{"Beta", "A1", "1", null});
        initialList.add(new String[]{"Beta", "A1", "2", null});
        initialList.add(new String[]{"Beta", "A2", "1", null});
        initialList.add(new String[]{"Beta", "A2", "2", null});

        ArrayList<JsonModel> returnList = new ArrayList<JsonModel>();

        HashMap<String,HashMap<String,JsonModel>> tempMap = new HashMap<String, HashMap<String,JsonModel>>();
        HashMap<String,JsonModel> tempMapOuterMost = new HashMap<String, JsonModel>();

        // eg. 1,null
        JsonModel layer3Child = null;

        // eg. A1,{}
        JsonModel layer2Child = null;

        // eg. Alpha,{}
        JsonModel layer1Child = null;

        for(String[] myArray: initialList){

            // to set inner most object eg. 1,null
            layer3Child = new JsonModel();
            layer3Child.setName(myArray[2]);

            JsonModel layer4Child = new JsonModel();
            layer4Child.setName("PersonName");
            ArrayList<JsonModel> layer4Children = new ArrayList<JsonModel>();
            layer4Children.add(layer4Child);
            layer3Child.setChildren(layer4Children);

            // getting object of outermost model eg. Alpha,{}
            if (tempMap.containsKey(myArray[0])){
                layer1Child = tempMapOuterMost.get(myArray[0]);
            } else {
                layer1Child = new JsonModel();
                layer1Child.setName(myArray[0]);
                layer1Child.setChildren(new ArrayList<JsonModel>());
                returnList.add(layer1Child);

                tempMapOuterMost.put(myArray[0], layer1Child);
                tempMap.put(myArray[0], new HashMap<String,JsonModel>());
            }

            // getting the object at layer 2 eg. A1,{}
            if (tempMap.get(myArray[0]).containsKey(myArray[1])){
                layer2Child = tempMap.get(myArray[0]).get(myArray[1]);
            } else {
                layer2Child = new JsonModel();
                layer2Child.setName(myArray[1]);
                layer2Child.setChildren(new ArrayList<JsonModel>());

                layer1Child.getChildren().add(layer2Child);

                tempMap.get(myArray[0]).put(myArray[1], layer2Child);
            }

            layer2Child.getChildren().add(layer3Child);
        }

        System.out.println(returnList);
    }

}

This is fantastic thank you very much. One last thing though, I have been trying to add this but am still very new at java. The null values are actually going to be people's names. How do add a layer4Child who's parent is layer3? — Ethan, Mar 10 '15 at 22:07
Ok, I got that part and after some string editing it works perfectly as json for my jstree! Lastly though, It is showing layer4 as also having children. I understand why it does this but how can I remove the children on the level 4 objects? — Ethan, Mar 11 '15 at 04:59
you will not have to remove the children, just set it to null. If its null, it will not be part of the resulting JSON. You can also modify the toString method to check for null. Something like: return "name: "+name + ((children == null) ? "" :", children: "+children+""); — Anshuman, Mar 11 '15 at 05:10

score 0 · Answer 2 · edited May 23 '17 at 12:06

Here is a really rough implementation of a basic Tree. It could use a bunch more improvements, like string builder, and generics.

Also you should look at this question and answers: Java tree data-structure?

I would also recommend reading a Data structures book like this: https://books.google.com/books?id=GEJ_Jp6mUpgC&dq=data+structures&source=gbs_navlinks_s

public Tree
{
    public String value;
    public List<Tree> children;

    public Tree(String value)
    {
        children = new ArrayList();
        this.value = value;
    }

    public void AddChild(Tree child)
    {
        children.Add(child);        
    }

    public String ToString()
    {
        String fullString = value;
        for(Tree child : children)
        {
            fullString += "\n";
            fullString += child.ToString();
        }

        return fullString;
    }
}

Generate Tree Structure from Arrays Java

2 Answers2