Sorting in Hash Maps in Java
- by Crystal
I'm trying to get familiar with Collections. I have a String which is my key, email address, and a Person object (firstName, lastName, telephone, email). I read in the Java collections chapter on Sun's webpages that if you had a HashMap and wanted it sorted, you could use a TreeMap. How does this sort work? Is it based on the compareTo() method you have in your Person class? I overrode the compareTo() method in my Person class to sort by lastName. But it isn't working properly and was wondering if I have the right idea or not. getSortedListByLastName at the bottom of this code is where I try to convert to a TreeMap. Also, if this is the correct way to do it, or one of the correct ways to do it, how do I then sort by firstName since my compareTo() is comparing by lastName.
import java.util.*;
public class OrganizeThis
{
/**
Add a person to the organizer
@param p A person object
*/
public void add(Person p)
{
staff.put(p.getEmail(), p);
//System.out.println("Person " + p + "added");
}
/**
* Remove a Person from the organizer.
*
* @param email The email of the person to be removed.
*/
public void remove(String email)
{
staff.remove(email);
}
/**
* Remove all contacts from the organizer.
*
*/
public void empty()
{
staff.clear();
}
/**
* Find the person stored in the organizer with the email address.
* Note, each person will have a unique email address.
*
* @param email The person email address you are looking for.
*
*/
public Person findByEmail(String email)
{
Person aPerson = staff.get(email);
return aPerson;
}
/**
* Find all persons stored in the organizer with the same last name.
* Note, there can be multiple persons with the same last name.
*
* @param lastName The last name of the persons your are looking for.
*
*/
public Person[] find(String lastName)
{
ArrayList<Person> names = new ArrayList<Person>();
for (Person s : staff.values())
{
if (s.getLastName() == lastName) {
names.add(s);
}
}
// Convert ArrayList back to Array
Person nameArray[] = new Person[names.size()];
names.toArray(nameArray);
return nameArray;
}
/**
* Return all the contact from the orgnizer in
* an array sorted by last name.
*
* @return An array of Person objects.
*
*/
public Person[] getSortedListByLastName()
{
Map<String, Person> sorted = new TreeMap<String, Person>(staff);
ArrayList<Person> sortedArrayList = new ArrayList<Person>();
for (Person s: sorted.values()) {
sortedArrayList.add(s);
}
Person sortedArray[] = new Person[sortedArrayList.size()];
sortedArrayList.toArray(sortedArray);
return sortedArray;
}
private Map<String, Person> staff = new HashMap<String, Person>();
public static void main(String[] args)
{
OrganizeThis testObj = new OrganizeThis();
Person person1 = new Person("J", "W", "111-222-3333", "[email protected]");
Person person2 = new Person("K", "W", "345-678-9999", "[email protected]");
Person person3 = new Person("Phoebe", "Wang", "322-111-3333", "[email protected]");
Person person4 = new Person("Nermal", "Johnson", "322-342-5555", "[email protected]");
Person person5 = new Person("Apple", "Banana", "123-456-1111", "[email protected]");
testObj.add(person1);
testObj.add(person2);
testObj.add(person3);
testObj.add(person4);
testObj.add(person5);
System.out.println(testObj.findByEmail("[email protected]"));
System.out.println("------------" + '\n');
Person a[] = testObj.find("W");
for (Person p : a)
System.out.println(p);
System.out.println("------------" + '\n');
a = testObj.find("W");
for (Person p : a)
System.out.println(p);
System.out.println("SORTED" + '\n');
a = testObj.getSortedListByLastName();
for (Person b : a) {
System.out.println(b);
}
}
}
Person class:
public class Person implements Comparable
{
String firstName;
String lastName;
String telephone;
String email;
public Person()
{
firstName = "";
lastName = "";
telephone = "";
email = "";
}
public Person(String firstName)
{
this.firstName = firstName;
}
public Person(String firstName, String lastName, String telephone, String email)
{
this.firstName = firstName;
this.lastName = lastName;
this.telephone = telephone;
this.email = email;
}
public String getFirstName()
{
return firstName;
}
public void setFirstName(String firstName)
{
this.firstName = firstName;
}
public String getLastName()
{
return lastName;
}
public void setLastName(String lastName)
{
this.lastName = lastName;
}
public String getTelephone()
{
return telephone;
}
public void setTelephone(String telephone)
{
this.telephone = telephone;
}
public String getEmail()
{
return email;
}
public void setEmail(String email)
{
this.email = email;
}
public int compareTo(Object o)
{
String s1 = this.lastName + this.firstName;
String s2 = ((Person) o).lastName + ((Person) o).firstName;
return s1.compareTo(s2);
}
public boolean equals(Object otherObject)
{
// a quick test to see if the objects are identical
if (this == otherObject) {
return true;
}
// must return false if the explicit parameter is null
if (otherObject == null) {
return false;
}
if (!(otherObject instanceof Person)) {
return false;
}
Person other = (Person) otherObject;
return firstName.equals(other.firstName) && lastName.equals(other.lastName) &&
telephone.equals(other.telephone) && email.equals(other.email);
}
public int hashCode()
{
return this.email.toLowerCase().hashCode();
}
public String toString()
{
return getClass().getName() + "[firstName = " + firstName + '\n'
+ "lastName = " + lastName + '\n'
+ "telephone = " + telephone + '\n'
+ "email = " + email + "]";
}
}
