Java Reference
In-Depth Information
Listing 7-2.
A SmartPoint Class That Reimplements equals() and hashCode() Methods
// SmartPoint.java
package com.jdojo.object;
public class SmartPoint {
private int x;
private int y;
public SmartPoint(int x, int y) {
this.x = x;
this.y = y;
}
/* Reimplement the equals() method */
public boolean equals(Object otherObject) {
// Are the same?
if (this == otherObject) {
return true;
}
// Is otherObject a null reference?
if (otherObject == null) {
return false;
}
// Do they belong to the same class?
if (this.getClass() != otherObject.getClass()) {
return false;
}
// Get the reference of otherObject in a SmartPoint variable
SmartPoint otherPoint = (SmartPoint)otherObject;
// Do they have the same x and y co-ordinates
boolean isSamePoint = (this.x == otherPoint.x && this.y == otherPoint.y);
return isSamePoint;
}
/* Reimplement hashCode() method of the Object class,
which is a requirement when you reimplement equals() method */
public int hashCode() {
return (this.x + this.y);
}
}
You call your new class
SmartPoint
. Java advises to reimplement
hashCode()
and
equals()
methods together
if any one of them is reimplemented in your class. The Java compiler would not complain if you reimplement the
equals()
method and not the
hashCode()
method. However, you will get unpredictable results when you use the
objects of your class in hash-based collections.
