get a comma separated string using java stream

Question

I have the following code using java Stream.

I am trying the get the function to build a string of value: "a,b" in this case. however, the output (separatedByComma in this case) is always "b".

Could somebody shed some light please?

@Test
public void testJoin() {
    List<MOccS> occList = new ArrayList<> (  );
    MOccS mOccS = new MOccS ();
    mOccS.setOccSCd ( "1" );
    mOccS.setOccSNm ( "a" );
    occList.add ( mOccS );

    MOccS mOccS2 = new MOccS ();
    mOccS2.setOccSCd ( "2" );
    mOccS2.setOccSNm ( "b" );
    occList.add ( mOccS2 );


    List<String> strings = new ArrayList<> (  );
    strings.add ( "1" );
    strings.add ( "2" );

    String separatedByComma = "";
    for(String word: strings) {
        separatedByComma = occList.stream ()
                                  .filter ( occ -> word.equalsIgnoreCase ( occ.getOccSCd () ) )         
                                  .map ( occ -> occ.getOccSNm () )
                                  .collect ( Collectors.joining ( "," ) );
     }

     System.out.println (separatedByComma);
}


class MOccS{
    String occSCd;
    String occSNm;
    ...
    getter/setter
    ...
}

Eran · Accepted Answer · 2018-11-14 08:41:03Z

35

Each iteration of your for loop overwrites the value of separatedByComma. The first iteration assigns the String "a" to it, and the second replaces it with "b".

You should Stream over the elements of the strings List in order to join the Strings that match each of them into a single output String:

String separatedByComma = 
    strings.stream()
           .flatMap(word -> occList.stream()
                                   .filter(occ -> word.equalsIgnoreCase (occ.getOccSCd()))
                                   .map (occ -> occ.getOccSNm()))
           .collect(Collectors.joining (","));

Output:

a,b

edited Nov 14, 2018 at 8:41

answered Nov 14, 2018 at 8:25

Eran

395k57 gold badges726 silver badges793 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

zaozaoer Over a year ago

Thank you very much, your solution produces exactly what I needed.

Anonymous · Accepted Answer · 2018-11-14 08:47:16Z

3

In your loop for(String word: strings) you overwrite your separatedByComma variable.

edited Nov 14, 2018 at 8:47

Anonymous

87.4k15 gold badges163 silver badges181 bronze badges

answered Nov 14, 2018 at 8:23

talex

20.8k3 gold badges34 silver badges71 bronze badges

3 Comments

zaozaoer Over a year ago

I think you are right, could you let me know how to fix it? sorry I am new to java stream...

talex Over a year ago

If you want to filter occList and allow only those which getOccSCd is in list of string I can give you code sample.

zaozaoer Over a year ago

thanks so much for your quick answer as well. It was very helpful!

Pribic Rubik · Accepted Answer · 2023-09-01 12:08:08Z

2

You can also use String.join(",", strings)

answered Sep 1, 2023 at 12:08

Pribic Rubik

413 bronze badges

Collectives™ on Stack Overflow

get a comma separated string using java stream

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related