用java写一个背单词程序，要求可以改变单词显示的速度；可以增加标记生词并记到生词本中；可以增加测试的功能（单词含义可以随机选4个词的含义来让用户选择）等等，写出该代码

以下是一个简单的背单词程序示例代码，实现了速度控制、生词本和测试功能。你可以根据自己的需求进行修改和优化。

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class WordLearningProgram {
    
    private ArrayList<String> wordList;
    private ArrayList<String> newWords;
    private int speed;
    
    public WordLearningProgram() {
        wordList = new ArrayList<String>();
        newWords = new ArrayList<String>();
        speed = 3; // 默认速度为3秒每个单词
    }
    
    public void addWord(String word) {
        wordList.add(word);
    }
    
    public void addNewWord(String word) {
        newWords.add(word);
    }
    
    public void setSpeed(int speed) {
        this.speed = speed;
    }
    
    public void startLearning() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        for (String word : wordList) {
            System.out.print(word);
            try {
                Thread.sleep(speed * 1000); // 控制显示速度
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.print("\r"); // 清除单词
            System.out.print(String.format("%" + word.length() + "s", "").replaceAll(" ", "-")); // 显示单词长度的横线
            System.out.print("\r");
            count++;
            if (count % 10 == 0) { // 每10个单词暂停一次
                System.out.print("按任意键继续...");
                scanner.nextLine();
            }
            if (newWords.contains(word)) { // 如果是生词，添加到生词本中
                System.out.print("生词！是否添加到生词本？(y/n)");
                String input = scanner.nextLine();
                if (input.equals("y")) {
                    newWords.remove(word);
                    System.out.println("已添加到生词本。");
                }
            }
        }
        System.out.println("已完成所有单词的学习。");
    }
    
    public void startTesting() {
        Scanner scanner = new Scanner(System.in);
        int correctCount = 0;
        while (true) {
            Collections.shuffle(wordList); // 随机单词顺序
            for (String word : wordList) {
                System.out.println("请选出单词 " + word + " 的含义：");
                ArrayList<String> options = new ArrayList<String>();
                options.add(word); // 正确答案
                while (options.size() < 4) { // 随机选出3个错误答案
                    String randomWord = wordList.get((int) (Math.random() * wordList.size()));
                    if (!options.contains(randomWord)) {
                        options.add(randomWord);
                    }
                }
                Collections.shuffle(options); // 随机选项顺序
                for (int i = 0; i < options.size(); i++) {
                    System.out.println((i + 1) + ". " + options.get(i));
                }
                int answer = 0;
                while (true) {
                    System.out.print("请输入答案编号：");
                    try {
                        answer = Integer.parseInt(scanner.nextLine());
                    } catch (NumberFormatException e) {
                        System.out.println("请输入数字！");
                        continue;
                    }
                    if (answer >= 1 && answer <= 4) {
                        break;
                    } else {
                        System.out.println("请输入1-4之间的数字！");
                    }
                }
                if (options.get(answer - 1).equals(word)) {
                    System.out.println("回答正确！");
                    correctCount++;
                } else {
                    System.out.println("回答错误！正确答案为：" + word);
                }
            }
            System.out.println("测试结束，共回答了 " + wordList.size() + " 题，" + correctCount + " 题回答正确。");
            System.out.print("是否重新测试？(y/n)");
            String input = scanner.nextLine();
            if (input.equals("n")) {
                break;
            }
        }
    }

    public static void main(String[] args) {
        WordLearningProgram program = new WordLearningProgram();
        program.addWord("apple");
        program.addWord("banana");
        program.addWord("cherry");
        program.addWord("date");
        program.addNewWord("elderberry");
        program.addNewWord("fig");
        program.setSpeed(5);
        program.startLearning();
        program.startTesting();
    }

}