Java Java Data Structures Organizing Data Interfaces

Xuanzheng Lin
Xuanzheng Lin
2,466 Points

The use of equals method in overriding the compareTo

Craig had the code like this

public int compareTo(Object obj) {
    Treet other = (Treet) obj;
    if (equals(other)) {
        return 0;

I wonder why not the equals method like the name of the object to be compared.equals(other)?

1 Answer

public class Treet implements Comparable {

.... @Override public int compareTo(Object obj) { //method takes in a class and returns an int

Treet other = (Treet) obj;                  //just placing the target into a variable class inst

if (equals(other)) {                        //if x.compareTo(y) == 0, return 0;

    return 0;                       //stop this method, they are the same

int dateCmp = mCreationDate.compareTo(other.mCreationDate); //otherwise keep going and compare the class' variables

    int descriptionCmp = description.compareTo(other.description);

    int authorCmp = author.compareTo(;

    if (dateCmp == 0) {                     //if similarities occur, return them

        if (descriptionCmp == 0) {

            return authorCmp;

        return descriptionCmp;

    return dateCmp;