Question

I learned about the Comparable interface, for which a class must implement compareTo method. A project I am using that method as:

public class EmployeeAssignmentTotal implements Comparable<EmployeeAssignmentTotal>, Serializable {

private Employee employee;
private int total;
....
public int compareTo(EmployeeAssignmentTotal other) {
    return new CompareToBuilder()
            .append(employee, other.employee)
            .append(total, other.total)
            .toComparison();
}

What exacly does CompareToBuilder do here? And how is it interacting with the employee and total attributes?

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I did read the javadocs, but I cant make head or tail of what they are doing with the constructor and the multiple appends. Does this question indicate unclear intentions and zero research?

Answer 1

This class is meant to assist you in building compareTo()-methods. Imagine you had more than just 2 fields in your class – manually coding your comparison-method could be quite cumbersome.

CompareToBuilder is doing that for you – each append() method is adding a new comparison, and all comparisons are &&ed.

So the code you posted runs equals() on the employee object and total.