五、使用依赖注入取代硬连接资源（静态工厂、单例），也可用于构造方法、bulider模式

//静态方法工具类
public class SpellChecker {
    private static final Lexicon dictiOnary= ...;

    private SpellChecker() {} // Noninstantiable

    public static boolean isValid(String word) { ... }
    public static List suggestions(String typo) { ... }
}

//单例
public class SpellChecker {
    private final Lexicon dictiOnary= ...;

    private SpellChecker(...) {}
    public static INSTANCE = new SpellChecker(...);

    public boolean isValid(String word) { ... }
    public List suggestions(String typo) { ... }
}

// Dependency injection provides flexibility and testability
public class SpellChecker {
    private final Lexicon dictionary;

    public SpellChecker(Lexicon dictionary) {
        this.dictiOnary= Objects.requireNonNull(dictionary);
    }

    public boolean isValid(String word) { ... }
    public List suggestions(String typo) { ... }
}