compare 2 lists in java [closed]

Answer 1

Create a wrapper class for your two classes and use List.retainAll(). Here is some code

You already have classes that are the equivalents of Blam and Hoot; they are included for completeness

public class Blam
{
    private String investmentNumber;
    private String investmentName;

    ... getters and setters
}

public class Hoot
{
    private String investmentNumber;
    private String propertyNumber;

    ... getters and setters
}

public class Wrapper
{
    private Blam blam;
    private Hoot hoot;

    public Wrapper(final Blam blam)
    {
        this.blam = blam;
    }

    public Wrapper(final Hoot hoot)
    {
        this.hoot = hoot;
    }

    public boolean equals(Object oThat)
    {
        if (this == oThat)
        {
            return true;
        }

        if (oThat instanceof Wrapper)
        {
            Wrapper wThat = (Wrapper)oThat;
            String myInvestmentNumber;
            String yourInvestmentNumber;

            if (blam != null)
            {
                myInvestmentNumber = blam.getInvestmentNumber();
            }
            else
            {
                myInvestmentNumber = hoot.getInvestmentNumber();
            }

            if (wThat.blam != null)
            {
                yourInvestmentNumber = wThat.blam.getInvestmentNumber();
            }
            else
            {
                yourInvestmentNumber = wThat.hoot.getInvestmentNumber();
            }

            return StringUtils.equals(myInvestmentNumber, yourInvestmentNumber);
        }

        return false;
    }

    public int hashCode()
    {
        ... implement this using blam and hoot as in equals() above.
    }

            ... getters for Hoot and Blam values as needed.
}


    List<Wrapper> listOne = new ArrayList<Wrapper>();
    List<Wrapper> listTwo = new ArrayList<Wrapper>();

    ... populate listOne with wrapped Blam values.
    ... populate listTwo with wrapped Hoot values.

    listTwo.retainAll(listOne);

After executing the retainAll, the Hoot list contains all the values from database 2 for which there was a corresponding entry in database 1.

Note: StringUtils is an apache commons lang class that performs a null safe equals (and other stuff).

Answer 2

If you have two list, you can do the following:

List<Integer> list1 = new ArrayList<>(Arrays.asList(1, 5, 6, 7));
List<Integer> list2 = new ArrayList<>(Arrays.asList(5, 6, 7, 8, 9));
list1.retainAll(list2);
System.out.println("list1 = " + list1);

And the result will be:

list1 = [5, 6, 7]

Answer 3

Suppose you have two pojos corresponding to two different table of two different datbase

Pojo1-------entity class corressponding to first table of first database

Pojo2-------entity class corressponding to second table of second database

 List<Pojo1> listOne = new ArrayList<Pojo1>();
  List<Pojo2> listTwo = new ArrayList<Pojo2>();
   listTwo.retainAll(listOne);

Note that in these two pojos you have to override hashcode() and equals() method of Object class, because in retainAll, you are comparing the objects of two pojos