implement Trie tree.java

class TrieNode {
    // Initialize your data structure here.
        boolean isword;
        TrieNode[] children;
    
    public TrieNode() {
        this.isword = false;
        this.children = new TrieNode[26];
    }
}

public class Trie {
    private TrieNode root;

    public Trie() {
        root = new TrieNode();
    }

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode node = root;
        for(int i = 0; i < word.length(); i++){
            int index = word.charAt(i) - 'a';
            if(node.children[index] == null){
                node.children[index] = new TrieNode();
            }
            // move to the next level
            node = node.children[index];
        }
        node.isword = true;
        
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode node = root;
        for(int i = 0; i < word.length(); i++){
            int index = word.charAt(i) - 'a';
            if(node.children[index] == null){
                return false;
            }
            node = node.children[index];
        }
        
        return node.isword;
        
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode node = root;
        for(int i = 0; i < prefix.length(); i++){
            int index = prefix.charAt(i) - 'a';
              if(node.children[index] == null){
                return false;
            }
            node = node.children[index];
        }
        // when the program runs to here, it means have
        return true;
    }
}

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.insert("somestring");
// trie.search("key");