Java Stream - Compile time Error - Type mismatch: cannot convert from Map<Object,Object> to Map<Integer,List<String>>

Question

I hava a simple code where i am converting a List of my custom class object into a Map>. The code is as follows:

List<NPDto> appList = new ArrayList<NPDto>(); 
//list gets populated though some other method

//Here is conerting code where i get compile time error
final Map<Integer, List<String>> appMap = appList.stream()
                                              .collect(
                                                Collectors.toMap(
                                                  np -> NumberUtils.toInt(np.getPId()),
                                                  np -> Arrays.asList(np.getAppsReceived().split(","))
                                              ));
// Here is my DTO                                              
public class NPDto {

    private String pId;
  private String appsReceived;

  public String getPId(){
    return pId;
  }

  public void setPId(String pId){
    this.pId = pId;
  }

  public String getAppsReceived(){
    return appsReceived;
  }

  public void setAppsReceived(String appsReceived){
    this.appsReceived = appsReceived;
  }
}

But, i am getting a compiler error as follows:

Type mismatch: cannot convert from Map<Object,Object> to Map<Integer,List<String>>

I am compiling with Java SE 8[1.8.0_91]

Don't know where i am wrong. Can anybody please help out?

Not my downvote but probably because you haven't shown us a minimal reproducible example. In particular show us the actual declarations of the getters in NPDto. Using incorrect method names can give this error. — greg-449
– greg-449, Commented Dec 2, 2016 at 9:55
You are missing a right parenthesis (the one that closes the collect method call). If it's a typo in your question, then include which compiler you are using (javac / Eclipse's compiler / ...), knowing that the latter may have problems with type inference. Compiles fine for me using javac 1.8.0_102. — Alexis C.
– Alexis C., Commented Dec 2, 2016 at 10:02

Eugene · Accepted Answer · 2016-12-02 10:06:37Z

1

you need to make a slight change as split returns a String [].

np -> Arrays.asList(np.getAppsReceived().split(","))

answered Dec 2, 2016 at 10:06

Eugene

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4 Comments

KayV Over a year ago

That is what i am converting this into a List using Arrays.asList

Eugene Over a year ago

@KaranVerma that's funny I took the same code you have and it compiles just file. What does NumberUtils return? an Integer I assume?

KayV Over a year ago

Yes it returns Integer.

Holger Over a year ago

I guess, its commons.apache NumberUtils.toInt, designed to make erroneous code even worse by silently converting null and empty strings to zeros…

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