Reddy Reddy - 1 year ago 55
Java Question

Duplicate items are not added to the list

I'm trying below java code and would want to add all the matching items to a list based on the input list. Below I've the input list, look up list and the return matching list. Currenlty, the below code fails when we have duplicate values in the input list. Can someone advice how I can resolve this ? Thanks in advance.

import java.time.YearMonth;
import java.util.*;
import static;

public class PeriodTest {

public static void main(String[] args) {

List<YearMonth> yearMonths = Arrays.asList(YearMonth.of(2016, 9), YearMonth.of(2016, 9));

//Look up
List<PeriodCode> periodCodes = Arrays.asList(new PeriodCode(2016, 9), new PeriodCode(2017, 9));

List<PeriodCode> actualOutput = -> yearMonths.contains(YearMonth.of(item.getYear(), item.getMonth()))).collect(toList());
List<PeriodCode> expectedOutput = Arrays.asList
new PeriodCode(2016, 9),
new PeriodCode(2016, 9)

System.out.print(actualOutput.size() == expectedOutput.size());//false 1 vs 2


private static class PeriodCode {

private int year;
private int month;

PeriodCode(int year, int month) {
this.year = year;
this.month = month;

public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof PeriodCode)) return false;

PeriodCode that = (PeriodCode) o;

if (year != that.year) return false;
return month == that.month;


public int hashCode() {
int result = year;
result = 31 * result + month;
return result;

int getYear() {
return year;

void setYear(int year) {
this.year = year;

int getMonth() {
return month;

void setMonth(int month) {
this.month = month;


Answer Source

It's not clear why you expect duplicates to be gone, since you haven't actually done anything to remove them.

Adding .distinct() to the stream chain might help, though.

UPDATE: write
    .flatMap(periodCode ->
            .filter(YearMonth.of(periodCode.getYear(), periodCode.getMonth())::equals)
            .map(ym -> periodCode))
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