How can I get distinct values of a specific column in arrayList

Question

Assume I have this arrayList :

ArrayList<Personne> personnes = new ArrayList<Personne>();
 Personne p1 = new Personne("001590842","51862499", "N5+", "1", "20170201","0");
 Personne p2 = new Personne("001590842","51862499", "X0", "1", "20150529", "1");
 Personne p3 = new Personne("001639055","51862517", "G3", "1", "20170201", "2");
 Personne p4 = new Personne("001639055","51862517", "G3", "1", "20170201", "2");
 Personne p5 = new Personne("001597135","51862517", "G3", "1", "20170201", "2");
 Personne p6 = new Personne("001597135","51862517", "G3", "1", "20170201", "2");
 Personne p7 = new Personne("002804935","00006178","G4","1","19870101","1");
 Personne p8 = new Personne("002804935","00009118","X0","1","19861201","1");
 Personne p9 = new Personne("002804935","00009957","N4+","1","19861229","1");
 Personne p10 = new Personne("002804935","00012970","B3++","1","20100227","1");
 personnes.add(p1);
 personnes.add(p2);
 personnes.add(p3);
 personnes.add(p4);
 personnes.add(p5);
 personnes.add(p6);
 personnes.add(p7);
 personnes.add(p8);
 personnes.add(p9);
 personnes.add(p10);

Then I want to get only distinct values of the first column. So the nedeed result should be :

001590842
001639055
002804935

Note that my Personne class is defined as :

public class Personne {
 private String IDT_GCT;
 private String IDC_PSE_PCL;
 private String IDC_CD_NOT;
 private String DA_PRM_CTR_ORDER;
 private String IDT_ETT_PSE;
 private String CD_NOT;
 public Personne(String IDT_GCT, String IDC_PSE_PCL, String IDC_CD_NOT,
 String DA_PRM_CTR_ORDER, String IDT_ETT_PSE, String CD_NOT) {
 this.IDT_GCT = IDT_GCT;
 this.IDC_PSE_PCL = IDC_PSE_PCL;
 this.IDC_CD_NOT = IDC_CD_NOT;
 this.DA_PRM_CTR_ORDER = DA_PRM_CTR_ORDER;
 this.IDT_ETT_PSE = IDT_ETT_PSE;
 this.CD_NOT = CD_NOT;
 }
 public String getIDC_CD_NOT() {
 return this.IDC_CD_NOT;
 }
 public String getIDC_PSE_PCL() {
 return this.IDC_PSE_PCL;
 }
 public String getDA_PRM_CTR_ORDER() {
 return this.DA_PRM_CTR_ORDER;
 }
 public String getIDT_ETT_PSE() {
 return this.IDT_ETT_PSE;
 }
 public String getCD_NOT() {
 return this.CD_NOT;
 }
 public String getIDT_GCT() {
 return this.IDT_GCT;
 }
}

So I need to get distinct values of IDT_GCT variable.

So I created this function to return this :

private static List DistinctValues (ArrayList<Personne> listPersonnes)
{
 List <String> outList = listPersonnes.stream().map(m -> m.get("IDT_GCT")).distinct().collect(Collectors.toList());
 return(outList);
}

But this returns an error :

Multiple markers at this line
 - Cannot infer type argument(s) for <R> map(Function<? super T,? extends R>)
 - The method get(String) is undefined for the type Personne
 - The type List is not generic; it cannot be parameterized with arguments <String>

How can I resolve it please ?

• Sambit: Override equals and hashcode for the class Personne and use HashSet instead of ArrayList.

Answer 1

The method get(String) is undefined for the type Personne

you should use getIDT_GCT() instead

• Dylan: This is the answer.

Answer 2

private List DistinctValues(ArrayList listPersonnes) { Set uniqueColumnValues = new HashSet <>(); // hash set contains unique values listPersonnes.forEach(item -> uniqueColumnValues.add(item.getIDT_GCT())); // add values to HashSet return uniqueColumnValues.stream().collect(Collectors.toList()); }