是否可以在 Java 中的一种方法中返回两个 ArrayList 值？

Is it Possible to Return Two ArrayList values in One method in java?

提问by Java Developer

Is there any way to return two values from one method....

有没有办法从一个方法返回两个值....

Example:

例子：

public Class Sample
{
  public List<Date> returnTwoArrayList()
   {
      List<Date> startDate=new ArrayList<Date>();

      List<Date> endDate=new ArrayList<Date>();

     //So I want to Return Two values startDate and endDate ...It is Possible????
   }
}

Edit:1

i'm calling this method into My Service class and in that Storing StartDateand endDateinto Database here these are Two different Columns

我将此方法调用到我的服务类中，在存储StartDate和endDate数据库中，这里有两个不同的列

**StartDate      endDate**
2012-12-01     2012-12-05
2012-12-01     2012-12-15
2012-12-02     2012-12-10
2012-12-20     2012-12-25
2012-12-25     2012-12-31

回答by Juvanis

You cannotreturn separate structures via one method call, but you can return a compositeof them. For example, returning a list of your lists would be a possible solution:

你无法通过一个方法调用返回独立的结构，但可以返回一个复合它们。例如，返回列表列表将是一个可能的解决方案：

   public List<List<Date>> returnTwoArrayList()
   {
      List<Date> startDates = new ArrayList<Date>();
      List<Date> endDates = new ArrayList<Date>();

      List<List<Date>> result = new ArrayList<List<Date>>();
      result.add(startDates);
      result.add(endDates);

      return result;
   }

You can use get()method to retrieve these lists later on. Suppose you have made a call like List<List<Date>> twoLists = returnTwoArrayList();then you can get startDateby calling twoLists.get(0)and similarly endDatewith twoLists.get(1)

您可以get()稍后使用方法来检索这些列表。假设你打了一个电话，List<List<Date>> twoLists = returnTwoArrayList();然后你可以startDate通过调用twoLists.get(0)和类似的方式endDate获得twoLists.get(1)

回答by Subhrajyoti Majumder

No you can not return two value from a method.

不，你不能从一个方法返回两个值。

Best way would be create a custom class with two field and return that object.

最好的方法是创建一个带有两个字段的自定义类并返回该对象。

class ObjectHolder{
    private List<Date> startDate=new ArrayList<Date>();
    private List<Date> endDate=new ArrayList<Date>();

    <getter & setter method>
}

and -

和 -

public ObjectHolder returnTwoArrayList(){
    ObjectHolder oh = new ObjectHolder();
    List<Date> startDate=new ArrayList<Date>();
    oh.setStartDate(startDate);
    List<Date> endDate=new ArrayList<Date>();
    oh.setEndDate(endDate);
    return oh;
}

回答by Peter Lawrey

You can

你可以

• provide one or both lists as argument(s) to populate.
• have two lists which are fields of the instance of the method and access these via getters.
• return an array of two lists or a list of lists.
• return a custom type which wrap the two lists. I wouldn't use getters, just makes the fields public.
• have a single list of intervals

• 提供一个或两个列表作为要填充的参数。
• 有两个列表，它们是方法实例的字段，并通过 getter 访问它们。
• 返回一个包含两个列表的数组或一个列表列表。
• 返回包装两个列表的自定义类型。我不会使用 getter，只是公开这些字段。
• 有一个间隔列表

I believe the last is the best solution.

我相信最后一个是最好的解决方案。

public class Sample {
  public List<Interval> returnListOfStartToEndDates() {
      List<Interval> intervals=new ArrayList<>();

      return intervals;
   }
}

Joda-time has an Intervalclass which is more efficient than creating two Date objects, but you can also create your own.

Joda-time 有一个Interval类，它比创建两个 Date 对象更有效，但您也可以创建自己的。

回答by Harsha Kasturi

Instead you can use Map like the following,

相反，您可以使用 Map 如下所示，

public Map<String, List<Date>> getBothDates() {
  List<Date> startDate = new ArrayList<Date>();
  List<Date> endDate = new ArrayList<Date>();
  Map<String, List<Date>> bothDates = new HashMap<String, List<Date>>();
  bothDates.put("startDate", startDate);
  bothDates.put("endDate", endDate);    
  return bothDates;
}

To fetch both dates simple iterate the map,

要获取两个日期，请简单地迭代地图，

public void printBothDates() {
   Map<String, List<Date>> bothDates = getBothDates();
   for(Entry<String, List<Date>> entry : bothDates.entrySet()) {
     if(StringUtils.equalsIgnoreCase("startDate", entry.getKey())) {
       for(Date d : entry.getValue()) {
          System.out.println("startDate---"+d);
       }
     } else if(StringUtils.equalsIgnoreCase("endDate", entry.getKey())) {
       for(Date d : entry.getValue()) {
          System.out.println("endDate---"+d);
       }
     }
   }
}

回答by Jeroen Vannevel

You could create a custom class like this

你可以像这样创建一个自定义类

TimeSpan(ArrayList<Date> startDate, ArrayList<Date> endDate)

and return that Object.

并返回该对象。

回答by Omaha

Directly, no, unless you count returning an array of two Lists, or a Listof Lists with the stated understanding to the caller that it would contain exactly two entries and what value each one would represent.

直接，不，除非你返回两个数组ListS，或者List的Lists的既定认识到主叫方，这将正好包含两个条目，什么珍视每一个将代表。

Other than that, you could always write a Pairclass and use that, which would be better because it removes the dependence on that assumption about the dimension of the return value, and you will find that a Pairtype comes in handy in many, many situations.

除此之外，您总是可以编写一个Pair类并使用它，这会更好，因为它消除了对返回值维度的假设的依赖，并且您会发现Pair类型在很多很多情况下都派上用场。