How do I remove objects from an arraylist which are present in another arraylist based on one member variable of the object in Java?

Question

I have a POJO class A with the below structure

class A{
private String var1;
private int var2;
private String var3;
}

I have two ArrayList<A> List1 and List2 with different size. I want to remove all elements in List1 which are already present in List2 and this equality needs to be checked with respect to the value stored in var2 .

I have already checked making the List a Hashset and using removeAll() . But this wont give the desired output since for the same var2 , var1 values differ.

Please help me solve this problem.

Edit 1 - Requested by Murat

public class HistoryDto implements Serializable,Comparable<HistoryDto> {

    private Integer id;
    private String sId;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getSId() {
        return sId;
    }

    public void setSId(String sId) {
        this.sId = sId;
    }

    public String getTrackName() {
        return trackName;
    }

    public void setTrackName(String trackName) {
        this.trackName = trackName;
    }

    public String getTrackDescription() {
        return trackDescription;
    }

    public void setTrackDescription(String trackDescription) {
        this.trackDescription = trackDescription;
    }

    public Integer getUsedNo() {
        return usedNo;
    }

    public void setUsedNo(Integer usedNo) {
        this.usedNo = usedNo;
    }

    public String getExtraInfo() {
        return extraInfo;
    }

    public void setExtraInfo(String extraInfo) {
        this.extraInfo = extraInfo;
    }

    public String getImageUrl() {
        return imageUrl;
    }

    public void setImageUrl(String imageUrl) {
        this.imageUrl = imageUrl;
    }

    public Integer getPartyId() {
        return partyId;
    }

    public void setPartyId(Integer partyId) {
        this.partyId = partyId;
    }

    private String trackName;
    private String trackDescription;
    private Integer usedNo;
    private String extraInfo;
    private String imageUrl;
    private Integer partyId;


    public int compareTo(HistoryDto other) {
        return this.sId.compareTo(other.sId);
    }


}

Removing Items

ListA.removeAll(new HashSet(listB));

Answer 1

You may do it using the Stream API :

Set<Integer> var2 = list2.stream()
    .map(a -> a.var2)
    .collect(Collectors.toSet());
list1.stream()
    .filter(a -> !var2.contains(a.var2))
    .collect(Collectors.toList());

Answer 2

You need 2 loops nested.

pseudocode:

for each in A do
    for each in B do
       if (current item of A equals to current item of B)
           say yes!
    done
done

You just need to translate it to Java.