Comparable Interface and compareTo() Method

This section provides a tutorial example on how to construct object with the Comparable interface, so that they can be stored in collections using the TreeSet class. Search operations on TreeSet class perform nicely - almost the same as HastSet and LinkedHashSet.

In order to use TreeSet collection, data elements must be comparable. So I enhanced MySimpleDate class and rename it as MyDate class:

 * Copyright (c) All Rights Reserved.
import java.util.*;
public class MyDate implements Comparable {
   private static Random r;
   private Date my_date;
   public MyDate () {
      my_date = new Date();
      long l = my_date.getTime();
      int i = (int) (l/1000/60/60/24);
      if (r==null) r = new Random();
      i = r.nextInt(i);
      l = ((long) i)*24*60*60*1000;
   public long getTime() {
      return my_date.getTime();
   public int compareTo(Object o) {
      if (getTime()<((MyDate) o).getTime()) return -1;
      else if (getTime()==((MyDate) o).getTime()) return 0;
      else return 1;
   public boolean equals(Object o) {
      return compareTo(o)==0;
   public int hashCode() {
      return (int)(getTime()^(getTime()>>>32));

Note that:

Using the MyDate class with my own compareTo(), equals(), and hashCode() methods, I repeated the search operation performance tests. Here is the results on Windows 2000 with JDK 1.4.1_01:

                  With MySimpleDate         With MyDate
Collection       Number of Elements      Number of Elements
Class           5000   10000   20000    5000   10000   20000

HashSet           10      20      20      70      10      30
LinkedHashSet      0      10      20       0      10      10
TreeSet          n/a     n/a     n/a      10      40      70
Vector           661    2714   10936    1502    9424   37626
ArrayList        651    2694   10676    1573    9314   37646
LinkedList       762    3305   28122    2193   14102   54902
TreeMap         1021   10256   52719    4276   18417   56205
HashMap         1712   12629   60050    4727   29024   92068
IdentityHashMap  391    1532    7000     381    1532    6980
WeakHashMap     1572  failed  failed  failed  failed  failed
Hashtable       3145   21261   89103    5518   23395   89094

The result shows that:

Table of Contents

 About This JDK Tutorial Book

 JDK (Java Development Kit)

 Java Date-Time API

 Date, Time and Calendar Classes

 Date and Time Object and String Conversion

 Number Object and Numeric String Conversion

 Locales, Localization Methods and Resource Bundles

 Calling and Importing Classes Defined in Unnamed Packages

HashSet, Vector, HashMap and Collection Classes

 Types of Collections of Elements

 Data Structures of Collection Implementations

 Collection Implementations in JDK

 Search Operation Performance of Different Collection Classes

Comparable Interface and compareTo() Method

 Character Set Encoding Classes and Methods

 Character Set Encoding Maps

 Encoding Conversion Programs for Encoded Text Files

 Java Logging

 Socket Network Communication

 Datagram Network Communication

 DOM (Document Object Model) - API for XML Files

 SAX (Simple API for XML)

 DTD (Document Type Definition) - XML Validation

 XSD (XML Schema Definition) - XML Validation

 XSL (Extensible Stylesheet Language)

 Message Digest Algorithm Implementations in JDK

 Private key and Public Key Pair Generation

 PKCS#8/X.509 Private/Public Encoding Standards

 Digital Signature Algorithm and Sample Program

 "keytool" Commands and "keystore" Files

 KeyStore and Certificate Classes

 Secret Key Generation and Management

 Cipher - Encryption and Decryption

 The SSL (Secure Socket Layer) Protocol

 SSL Socket Communication Testing Programs

 SSL Client Authentication

 HTTPS (Hypertext Transfer Protocol Secure)

 Outdated Tutorials


 Full Version in PDF/EPUB