如何编写Java方法返回allPeopleFromTable和visibleInfo两个HashSet？

在Java中无法直接返回多个值，但可以通过以下几种方式实现同时返回两个HashSet的需求：

方案一：自定义结果封装类（推荐） #

创建一个专门的类来封装需要返回的两个集合，语义清晰且易于维护：

// 自定义结果类，封装两个Set
class PeopleSetsResult {
    private final Set<People> allPeople;
    private final Set<People> visiblePeople;

    public PeopleSetsResult(Set<People> allPeople, Set<People> visiblePeople) {
        this.allPeople = allPeople;
        this.visiblePeople = visiblePeople;
    }

    // Getter方法，供外部获取集合
    public Set<People> getAllPeople() {
        return allPeople;
    }

    public Set<People> getVisiblePeople() {
        return visiblePeople;
    }
}

// 封装后的业务方法
public PeopleSetsResult processPeopleResults(List<ResultSet> resultSets) {
    Set<People> allPeopleFromTable = new HashSet<>();
    Set<People> visibleInfo = new HashSet<>();

    for (ResultSet rs : resultSets) {
        try {
            while (rs.next()) {
                final People people = new People(rs); // 原代码中Table应为People实体类，此处修正
                allPeopleFromTable.add(people);
                if (isVisible(people)) {
                    visibleInfo.add(people);
                }
            }
        } catch (SQLException e) {
            // 添加异常处理，如打印日志或抛出自定义异常
            e.printStackTrace();
        }
    }

    return new PeopleSetsResult(allPeopleFromTable, visibleInfo);
}

// 调用示例
public static void main(String[] args) {
    // 假设已获取resultSets
    List<ResultSet> resultSets = ...;
    YourClass instance = new YourClass();
    PeopleSetsResult result = instance.processPeopleResults(resultSets);
    
    Set<People> allPeople = result.getAllPeople();
    Set<People> visiblePeople = result.getVisiblePeople();
}

方案二：返回包含两个Set的数组 #

如果不想额外创建类，可以返回一个Set[]数组，但需注意元素顺序，可读性稍差：

public Set<People>[] processPeopleResults(List<ResultSet> resultSets) {
    Set<People> allPeopleFromTable = new HashSet<>();
    Set<People> visibleInfo = new HashSet<>();

    // 业务逻辑同方案一...

    @SuppressWarnings("unchecked")
    Set<People>[] result = new Set[]{allPeopleFromTable, visibleInfo};
    return result;
}

// 调用示例
public static void main(String[] args) {
    Set<People>[] result = processPeopleResults(resultSets);
    Set<People> allPeople = result[0];
    Set<People> visiblePeople = result[1];
}

方案三：使用Map存储返回结果 #

用Map的键区分两个集合，可读性不如自定义类：

public Map<String, Set<People>> processPeopleResults(List<ResultSet> resultSets) {
    Set<People> allPeopleFromTable = new HashSet<>();
    Set<People> visibleInfo = new HashSet<>();

    // 业务逻辑同方案一...

    Map<String, Set<People>> resultMap = new HashMap<>();
    resultMap.put("allPeople", allPeopleFromTable);
    resultMap.put("visiblePeople", visibleInfo);
    return resultMap;
}

// 调用示例
public static void main(String[] args) {
    Map<String, Set<People>> resultMap = processPeopleResults(resultSets);
    Set<People> allPeople = resultMap.get("allPeople");
    Set<People> visiblePeople = resultMap.get("visiblePeople");
}

注意事项 #

1. 原代码中final Table people = new Table(rs);应为People实体类实例，需根据实际情况修正。
2. 处理ResultSet时必须捕获SQLException，避免未处理异常。
3. 优先选择方案一，自定义类能明确表达返回值含义，后续维护和扩展更方便。

内容的提问来源于stack exchange，提问作者pralxx