Java实体设计：利用泛型实现条件属性的类型安全管理

public enum TokenType {
    BASIC,
    LOCALIZED
}

public class Token {
    private String id;
    private String value;
    private TokenType type;
    private List<String> locales; // 即使不使用，也存在于所有Token实例中

    // 构造函数、其他getter/setter

    public Optional<List<String>> getLocales() {
        if (this.type == TokenType.LOCALIZED) {
            return Optional.ofNullable(locales);
        }
        return Optional.empty();
    }
}

// 使用示例
public class TokenService {
    public void processToken(Token token) {
        if (token.getType() == TokenType.LOCALIZED) {
            token.getLocales().ifPresent(l -> {
                System.out.println("Processing localized token with locales: " + l);
            });
        } else {
            System.out.println("Processing basic token.");
        }
    }
}

// 1. 定义通用Token接口
public interface Token {
    String getId();
    String getValue();
    // 其他通用方法
}

// 2. 实现基本Token
public class BasicToken implements Token {
    private String id;
    private String value;

    public BasicToken(String id, String value) {
        this.id = id;
        this.value = value;
    }

    @Override
    public String getId() { return id; }
    @Override
    public String getValue() { return value; }
}

// 3. 实现带有Locales的Token
public class LocalizedToken extends BasicToken {
    private List<String> locales;

    public LocalizedToken(String id, String value, List<String> locales) {
        super(id, value);
        this.locales = locales;
    }

    public List<String> getLocales() {
        return locales;
    }
}

// 4. 使用泛型约束的用例服务
public class TokenCreationService {

    // 通用创建方法，适用于任何类型的Token
    public <T extends Token> T createToken(String id, String value, Class<T> tokenType) {
        if (tokenType.equals(BasicToken.class)) {
            return (T) new BasicToken(id, value);
        }
        // 更复杂的创建逻辑，可能需要工厂模式
        throw new IllegalArgumentException("Unsupported token type: " + tokenType.getName());
    }

    // 专门处理LocalizedToken的用例
    public LocalizedToken createLocalizedToken(String id, String value, List<String> locales) {
        return new LocalizedToken(id, value, locales);
    }

    public <T extends Token> void processTokens(List<T> tokens) {
        for (T token : tokens) {
            System.out.println("Processing token with ID: " + token.getId());
            // 只有当token是LocalizedToken类型时，才能访问getLocales()
            if (token instanceof LocalizedToken) {
                LocalizedToken localizedToken = (LocalizedToken) token;
                System.out.println("  Locales: " + localizedToken.getLocales());
            }
        }
    }

    // 针对LocalizedToken的特定处理方法
    public void processLocalizedToken(LocalizedToken localizedToken) {
        System.out.println("Processing localized token with ID: " + localizedToken.getId() + " and locales: " + localizedToken.getLocales());
    }
}