compare 2 lists in java [closed]

问题

I am getting data from the two different databases and storing them in the java.util.List

Elements of database:1 
column 1                   column 2
**Investment Number**     Investment Name
123                         abcwe
124                         agsdf
454                         lkjcv
784                         ojncv
478                         hfdgh
852                         qweyu
745                         mmkty
201                         pbckl
560                         jklfg
741                         nbvbn

storing them in list1

Elements of database:2

column 1                   column 2
Investment Number     Property Number
123                         548
980                         743
454                         200
350                         357
478                         698
852                         223
745                         795
784                         213
341                         022
741                         900

storing them in list2

need to compare according to the Investment Numbers if Investment Number of list1 available in list2 then need to keep and discard others.

Thanks,

回答1:

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]

回答2:

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).

回答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

来源：https://stackoverflow.com/questions/21611881/compare-2-lists-in-java

标签

java

collections

arraylist