Question

I have two array list. Each has list of Objects of type Employee.

The Employee class looks like below

    public class Employee {

    private int id; // this is the primary key from employee table

    private String firstname;

    private String lastname;

    private String employeeId; // manually assigned unique id to each employee

    private float fte;

    Employee(String firstname, String lastname, String employeeId, float fte) {
        this.firstname = firstname;
        this.lastname = lastname;
        this.employeeId = employeeId;
        this.fte = fte;
    }

    // getters and setters
}

Employee id is manually generated unique id given to each employee.

I need to find the common employees between the two lists based on a employee id which have different fte’s.

    import java.util.ArrayList;
import java.util.List;

public class FindFTEDifferencesBetweenMatchingEmployeeIds {

    public static void main(String args[]) {
        List<Employee> list1 = new ArrayList<Employee>();
        List<Employee> list2 = new ArrayList<Employee>();

        list1.add(new Employee("F1", "L1", "EMP01", 1));
        list1.add(new Employee("F2", "L2", "EMP02", 1));
        list1.add(new Employee("F3", "L3", "EMP03", 1));
        list1.add(new Employee("F4", "L4", "EMP04", 1));
        list1.add(new Employee("F5", "L5", "EMP05", 1));
        list1.add(new Employee("F9", "L9", "EMP09", 0.7F));

        list2.add(new Employee("F1", "L1", "EMP01", 0.8F));
        list2.add(new Employee("F2", "L2", "EMP02", 1));
        list2.add(new Employee("F6", "L6", "EMP06", 1));
        list2.add(new Employee("F7", "L7", "EMP07", 1));
        list2.add(new Employee("F8", "L8", "EMP08", 1));
        list2.add(new Employee("F9", "L9", "EMP09", 1));

        List<FTEDifferences> commonInBothListWithDifferentFTE = new ArrayList<FTEDifferences>();
        // this should contain EMP01 and EMP09
        // since EMP02 has same FTE in both lists, it is ignored. 


    }
}

Employees with employee id EMP01 and EMP09 are common in both lists and they also have different ftes in each list.

So, I would want to have another list which contains these two employees.

    public class FTEDifferences {

    private Employee fromList1;

    private Employee fromList2;

    public Employee getFromList1() {
        return fromList1;
    }

    public void setFromList1(Employee fromList1) {
        this.fromList1 = fromList1;
    }

    public Employee getFromList2() {
        return fromList2;
    }

    public void setFromList2(Employee fromList2) {
        this.fromList2 = fromList2;
    }
}

Please help.

PS. Even though it will be easy to do this in SQL, I can not do it in SQL query as I can not modify the queries. I only need to work with the two given lists. 🙁

Answer 1

Override equals method like below.

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Employee other = (Employee) obj;
    if (employeeId == null) {
        if (other.employeeId != null)
            return false;
    } else if (!employeeId.equals(other.employeeId))
        return false;
    if (firstname == null) {
        if (other.firstname != null)
            return false;
    } else if (!firstname.equals(other.firstname))
        return false;
    if (Float.floatToIntBits(fte) == Float.floatToIntBits(other.fte))
        return false;
    if (lastname == null) {
        if (other.lastname != null)
            return false;
    } else if (!lastname.equals(other.lastname))
        return false;
    return true;
}

Then Create a finalList list and add list1 to it. Then call retainAll on finalList list with list2 which will give you common Employees based on employeeId

   List<Employee> finalList=new ArrayList<Employee>();
    finalList.addAll(list1);
    finalList.retainAll(list2);
    List<Employee> commonInBothListWithDifferentFTE=finalList;
    System.out.println(commonInBothListWithDifferentFTE);

Output:

[Employee [firstname=F1, lastname=L1, employeeId=EMP01, fte=1.0], Employee [firstname=F9, lastname=L9, employeeId=EMP09, fte=0.7]]