Java 对于 Hangman 游戏，索引 0 超出长度 0 的范围

Why the console said Index 0 out of bounds for length 0?
It says in my method CharacterSearch().

这是我的代码.顺便说一下，代码是Hangman Game.我对Java是个新手，并不了解所有的库.

package besingaPi_LE_3_2;

import java.util.Scanner;

public class GameHangman {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int miss = 0; 
        String choice1;
        String temp;
        
        String[] words = {"giraffe", "hipopotamus", "gorilla", "peacock", "armadillo"};

        int choice;
        //do {
            mainMenu();
            choice = input.nextInt();
            System.out.println();
            if(choice == 1){
                
                String wordRandom = Randomizer(words);
//              char[] letters = new char[wordRandom.length()];
                String mute  = secretWord(wordRandom);
                temp = mute;
//              char c = wordRandom.charAt(3);
//              System.out.println(c);
                System.out.println(wordRandom);
                System.out.println("Note: use only small character/s");
                
                while(!mute.equals(wordRandom)) {
                    System.out.print("(Guess) Enter a letter in word " + mute + " > ");         
                    choice1 = input.nextLine();
//                  char letter = choice1.charAt(0);
                    mute = CharacterSearch(wordRandom, mute, choice1);

                    if(temp.equals(mute)) {
                        miss++;
                    }
                    temp = mute;
    
                }
                System.out.println("The word is " + wordRandom + "." + " You missed " + miss + " time.");
            }
            else if (choice == 0) {
                System.out.println("Thank you!!");
                return;
            }

    }
    public static void mainMenu() {
        System.out.println("Welcome to Hangman");  
        System.out.println("[1]START\n[0]EXIT"); 
        System.out.print("Please input your choice: ");
        return; 
    }
    public static String CharacterSearch(String word, String muted, String key) {
        StringBuilder update = new StringBuilder(muted);
        int i;
        for(i = 0; i < word.length(); i++) {
            if(word.charAt(i)  == key.charAt(0)) {
                update.setCharAt(i,key.charAt(0));
            }
        }
        
        muted = update.toString();
        return muted;
    }
    public static String secretWord(String word) {
        String temp = "";
        for(int i = 0; i < word.length(); i++) {
            temp += "*";
        }
        return temp;
    }
    
    public static String Randomizer(String[] words) {
        int rand = (int)(Math.random() * words.length);
        String word = words[rand];
        return word;
    }
}

我try 了这么多东西，但它总是会说Index Out Out.