Any good examples of using hashCode?

Question

I am creating a simple test class of a date object using getYear, getMonth, GetDay, compareTo, equals and hashCode. Ive got everything else working fine, but im wondering if I am getting the correct output from the hashCode method. What exactly does the hashCode method do? anyone got a good example of using it and what it outputs?

Answer 1

the name of my date class - here's the rest of my code if you want to verify it:
package Final;
import java.util.GregorianCalendar;
import java.util.Calendar;
public class SimpleDate
/** Creates a new instance of SimpleDate
public SimpleDate()
     GregorianCalendar greg = new GregorianCalendar();
          year = greg.get(Calendar.YEAR);
          month = 1 + greg.get(Calendar.MONTH);
          day = greg.get(Calendar.DATE);
/** Creates the setDate method which allows the day, month, and year of the
* date to be specified
public SimpleDate( int year, int month, int day )
setDate( year, month, day );
/** Sets the day, month, and year variables for the date
public void setDate( int year, int month, int day )
GregorianCalendar greg = new GregorianCalendar();
greg.set(Calendar.YEAR, year);
greg.set(Calendar.MONTH, month-1);
greg.set(Calendar.DATE, day);
this.year = greg.get(Calendar.YEAR);
this.month = 1 + greg.get(Calendar.MONTH);
this.day = greg.get(Calendar.DATE);
/** Defines the method getYear which gets the integer value which represents
* the year in the date
* @returns int year
public int getYear()
return year;
/** Defines the method getMonth which gets the integer value which represents
* the month in the date
* @returns int month
public int getMonth()
return month;
/** Defines the method getDay which gets the integer value which represents
* the day in the date
* @returns int day
public int getDay()
return day;
/** Defines the boolean method equals which compares two dates to see if they
* are equal
* @returns boolean equals
public boolean equals()
return equals;
public int compareTo()
return comparable;
public int hashCode()
return hashcode;
public String toString()
String string1 = new String();
return string1;
/*************Built-in Self Test************/
public static void main(String[] args)
SimpleDate date = new SimpleDate();
SimpleDate date2 = new SimpleDate();
date.setDate(2005, 11, 4);
System.out.println("Day, Month and Year: " + day + " " + month + " " + year);
date.getYear();
System.out.println("The year selected is: " + year);
date.getMonth();
System.out.println("The month selected is: " + month);
date.getDay();
System.out.println("The day selected is: " + day);
date2.setDate(2004, 11, 4);
System.out.println("The first date selected equals the second date selected: " + date.equals(date2));
//System.out.println("The first date selected is comparable to the second date selected: " + date.compareTo(date2));
//How do I implement compareTo?
System.out.println("The hashcode for the first date selected is: " + date.hashCode());
System.out.println("The hashcode for the second date selected is: " + date2.hashCode());
// ***** Instance Variables *****
static int year;
static int month;
static int day;
boolean equals;
int comparable;
int hashcode;
}