I’m working on an Exact string matching with Suffix Trie, but I have problems in adding child nodes to the suffix trie as it keep returning null. I can’t figure out why my code keeps returning no matter I do anything.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class SuffixTrie {

private SuffixTrieNode root = new SuffixTrieNode();


public SuffixTrieNode insert(String str, int startPosition) {
    SuffixTrieNode current = root;
    for (int i = 0; i < str.length(); i++) {
        char c = str.charAt(i);
        SuffixTrieNode child = current.getChild(c);
        if (child == null) {
            child = new SuffixTrieNode();
            current.addChild(c, child);
        }
        current = child;

    }
    current.addData(startPosition, 0);

    if (current.data == null) {
        current.data = new SuffixTrieData();
    }

    return current;
}


 public SuffixTrieNode get(String str) {
    SuffixTrieNode current = root;
    for (int i = 0; i < str.length(); i++) {
        char c = str.charAt(i);
        current = current.getChild(c);

        // If current is null at any point, it means the substring does not exist
        if (current == null) {
            return null;
        }
    }
    return current;
}



public static SuffixTrie readInFromFile(String fileName) {
    SuffixTrie trie = new SuffixTrie();
    try (BufferedReader br = new BufferedReader(new FileReader(fileName))) {
        String line;
        int sentencePosition = 0;
        while ((line = br.readLine()) != null) {
            trie.insert(line, sentencePosition);
            sentencePosition++;
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    return trie;

}
 }

 import java.util.HashMap;

 public class SuffixTrieNode {

SuffixTrieData data = null;
int numChildren = 0;
private final HashMap<Character, SuffixTrieNode> children;

public SuffixTrieNode() {
    this.children = new HashMap<>();
}

public SuffixTrieNode getChild(char label) {
    return this.children.get(label);
}


public void addChild(char label, SuffixTrieNode node) {
    this.children.put(label, node);
    numChildren++;
}

public void addData(int sentencePos, int characterPos) {
    if (data == null) {
        data = new SuffixTrieData();
    }
    data.addStartIndex(new SuffixIndex(sentencePos, characterPos));
}

public String toString() {
    if (data != null) {
        return data.toString();
    } else {
        return null;
    }
}
}

import java.util.*;

public class SuffixTrieDriver {

public static void main(String[] args) {

    Scanner in = new Scanner(System.in);
    String fileName = in.nextLine();
    Queue<String> ss = new ArrayDeque<>();

    String suffix = in.nextLine();

    while (!suffix.equals(""))
    {
        ss.offer(suffix);
        suffix = in.nextLine();
    }

    SuffixTrie st = SuffixTrie.readInFromFile(fileName);

    while (!ss.isEmpty()) {
        String s = ss.poll();
        SuffixTrieNode sn = st.get(s);
        System.out.println("[" + s + "]: " + sn);
    }
}
 }

import java.util.ArrayList;

public class SuffixTrieData {

private final ArrayList<SuffixIndex> startIndexes = new ArrayList<>();

public void addStartIndex(SuffixIndex startIndex) {
    startIndexes.add(startIndex);
}

public String toString() {
    return startIndexes.toString();
}
}


public class SuffixIndex {

int sentence;
int character;

public SuffixIndex(int sentence, int character) {
    this.sentence = sentence;
    this.character = character;
}

public int getSentence() {
    return sentence;
}

public void setSentence(int sentence) {
    this.sentence = sentence;
}

public int getCharacter() {
    return character;
}

public void setCharacter(int character) {
    this.character = character;
}

/**
 * The sentence and character position in the format sentence.character notation
 * @return the position.
 */
@Override
public String toString() {
    return sentence + "." + character;
}

}`

The above is all the classes I’ve got.

the output I get is this

  `SuffixTrie/data/Frank02.txt

and
the
, the
onster
ngeuhhh
ing? This

 [and]: null
 [the]: null
 [, the]: null
 [onster]: null
 [ngeuhhh]: null
 [ing? This]: null`

But the output I want is

 `[and]: [1.27, 1.87, 3.34, 3.153, 4.15, 6.70, 7.66, 7.148, 8.88, 9.100, 9.124, 9.177,      9.203, 10.17, 12.67, 12.91, 13.97, 13.114, 14.27, 14.90]

[the]: [0.58, 1.116, 3.51, 3.96, 5.39, 7.36, 7.48, 7.127, 8.1, 8.18, 8.76, 9.1, 9.89, 9.232, 9.253, 10.57, 10.74, 12.7, 12.22, 12.56, 12.158, 13.42, 13.65, 13.144, 14.1, 14.31, 14.146, 15.19, 15.69, 15.133, 15.184, 15.288, 15.302]
[, the]: [8.16]
[onster]: null
[monst]: null`

 I tried making adjustments  to`your text` addChild(), getChild() methods but didn't work.