How to return an Integer or int and a list from a method in java?

Question

I am trying to return an int and a list from a method from a class. but i cant make object of that class. so how should i do it.

i try to do this :

        List listofObj = new ArrayList();
        List list1 = some code that i can't share;
        Integer total = some integer value;

        listOfObj.add((List) list1 );
        listOfObj.add((Integer) total);

        return listofObj;

but when i use it in another class -

        if (listOfObj != null && listOfObj.size() > 0) {

            List mainList = promoData.get(0); --- gives error
        count = (Integer) promoData.get(1);
        }

so i tried this ---

        if (listOfObj != null && listOfObj.size() > 0) {
            Map promoData = (Map) listOfObj;
            List mainList = (List) promoData.get(0);
            count = (Integer) promoData.get(1);
        }

but it still gives error when i hit the application.

error : java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.Map

"gives error" --> The error message always contains valuable information. Never forget to post it. — jlordo
– jlordo, Commented Jul 24, 2013 at 10:11

Community · Accepted Answer · 2017-05-23 12:29:19Z

4

A possible simple solution would be to create a class that has int and List<T> members and return an instance of that class.

Possibly relevant: What is the equivalent of the C++ Pair<L,R> in Java? for example implementations of a generic pair class.

edited May 23, 2017 at 12:29

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answered Jul 24, 2013 at 10:11

hmjd

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Comments

Itay Maman · Accepted Answer · 2013-07-24 10:57:51Z

2

You can use a pair class

public class Pair<X,Y> {
   public final X first;
   public final Y second;

   public Pair(X first, Y second) { this.first = first; this.second = second; }

   public static<XX,YY> of(XX xx, YY yy) { return new Pair<XX,YY>(xx, yy); }
}

Then define your method as follows:

 public Pair<List, Integer> myMethod() { 
    List someList = ...;
    int someInt = ....;
    ...
    return Pair.of(someList, someInt); 
 }

In the caller side:

Pair<List, Integer> pair = myMethod();
List mainList = pair.first;
int count = pair.second;

If you have the Guava library you can use a Pair class from there.

If you want to use a map, you will have to do a downcast on its values:

public Map<String, Object> myMethod() { 
  List someList = ...;
  int someInt = ....;
  ...
  Map<String, Object> map = new HashMap<String, Object>();
  map.put("list", someList);
  map.put("count", someInt);
  return map;
}

In the caller side:

Map<String, Object> map = myMethod();
List mainList = (List) map.get("list");
int count = (Integer) map.get("count");

edited Jul 24, 2013 at 10:57

answered Jul 24, 2013 at 10:12

Itay Maman

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2 Comments

newProgramer Over a year ago

can i use map instead. if yes can you please suggest how. Thanks

Itay Maman Over a year ago

Updated the answer. Please take another look.

Uwe Plonus · Accepted Answer · 2013-07-24 10:13:41Z

1

There are several possibilities:

First you can create a class containing a List and the int.

The next possibility is to return an Object[]. The disadvantage of this is that you lose the type safety.

The third possibility is to provide the list into the method call and fill it there and only return the int.

answered Jul 24, 2013 at 10:13

Uwe Plonus

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Comments

Sorin · Accepted Answer · 2013-07-24 10:16:03Z

1

Two solutions that came into my mind:

Make a class that has an int and an ArrayList and return an instance of that class. I would recommend this.
Initialize the ArrayList outside of your method and send it as a parameter. The method has to return only the int value because the changes made to the ArrayList will be seen outside of your method.

answered Jul 24, 2013 at 10:16

Sorin

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