Stuck using the Comparable Interface

Question

I am having problems implementing the Comparable Interface in my class. I have written the compareTo method but this is not working. Can anyone see what I am doing wrong in the coding of this method. Thanks !!. (see below code for the class :
package tma02q1;
import java.util.*;
This is the outline of the basic Video class.
Such a class describes the videos stocked by a branch of a video hire company
As well as completing the given methods you will need to make further additions
to this class.For further details you should study the BranchTest class.
public class Video implements Comparable {
// declare two instance variables
// a String to hold the video title
// an int to hold the video rental cost - cost is held in pence
private String aTitle;
private int aCost;
public Video(String aTitle, int aCost) {
this.aTitle = aTitle;
this.aCost = aCost;
private void setTitle(String aTitle) {
this.aTitle = aTitle;
public String getTitle() {
return aTitle;
private void setRentalCost(int aCost) {
this.aCost = aCost;
public int getRentalCost() {
return aCost;
public String toString() {
return "Video Title = " + aTitle + " which has a rental cost of = " + aCost;
public boolean equals(Object vid) {
Video arg = (Video) vid;
return (this.aTitle.equals(arg.aTitle)
&&this.aCost==arg.aCost);
public int compareTo(Object vido) {
Video arg = (Video) vido;
int comp = aCost.compareTo(arg.aCost);
return comp;

Answer 1

You've got another serious problem with your code. Both the equals and compareTo methods will throw a ClassCastException if the parameter is not a reference to a video object. Using the instanceof operator will however solve the problem. E.g.
public boolean equals(Object o) {
  if (o instanceof Video) {
    Video  arg = (Video) o;
    return (this.aTitle.equals(arg.aTitle)
            &&this.aCost == arg.aCost);
  else
    return false;  
}The same approach is applicable to the compareTo method.
Regards