How to compare elements of two generic lists in java?

Question

I have two generic list of Data Type class:RequiredList & PrimaryList

   public class Data{
        private String dataCode;
        private String dataDesc; 

        public String getDataCode(){}

        public void setDataCode(String dataCode){}

        public String getDataDesc(){}

        public void setDataDesc(String dataDesc){}


        }

    public static void main(String[] args) {
        List<Data> primaryList = new ArrayList<Data>();
        for (int i = 2; i < 5; i++) {
            Data data = new Data();
            data.setDataCode("code" + i);
            data.setDataDesc("desc" + i);
            primaryList.add(data);
        }

        List<Data> requiredList = new ArrayList<Data>();
        for (int i = 0; i < 8; i++) {
            Data data = new Data();
            data.setDataCode("code" + i);
            data.setDataDesc("desc" + i);
            requiredList.add(data);

        }
        StringBuffer partyList = new StringBuffer();
        for (int i = 0; i < requiredList.size(); i++) {
            if (primaryList.size() > i
                    && !requiredList.get(i).getDataCode().equals(primaryList.get(i).getDataCode())) {
                partyList.append(requiredList.get(i).getDataDesc());
                partyList.append(",");

            }
            if(primaryList.size() <= i)
            {
                partyList.append(requiredList.get(i).getDataDesc());
                partyList.append(",");
            }           
        }
        System.out.println(partyList.toString());
    }

I want to compare elements of requiredList to elements of primaryList.Those elements of primaryList are not present in requiredList , they will be added in new list.Can anybody help me out?

Answer 1

First you need to implement equals() and hashcode() for Data

Then

List<Data> newlist = new ArrayList<Data>();
for(Data data : primaryList ) {
   if(!requiredList.contains(data) ) {
       newlist.add(data);
   }
 } 

Answer 2

If you okay to modify primaryList then removeAll would do the trick

primaryList.removeAll(requiredList);

As @Subin S pointed out equals and hashCode need to be overriden for Data .

Answer 3

Those elements of primaryList are not present in requiredList , they will be added in new list.

Look at the List removeAll() or retainAll() methods are useful in your usecase.