OpenWritings.net

/**
 * Removing all characters but letters and numbers.
 * @author Xuan Ngo
 *
 */
public class StrippingUnwantedChars
{
 
  public static void main(String[] args)
  {
    String s = "Good Morning, today is 1900-12-31.";
 
    /**
     * Replace characters that are NOT lowercase letters(a-z), uppercase 
     *  letters(A-Z) or numbers(0-9) with empty string.
     */
    s = s.replaceAll("[^a-zA-Z0-9]", "");
 
    System.out.println(s); // Output: GoodMorningtodayis19001231
  }
 
}

log4j.rootLogger=info, R
log4j.appender.R=org.apache.log4j.DailyRollingFileAppender
log4j.appender.R.File=filename
log4j.appender.R.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss.SSS zzz} %5p %c{1}:%L - %m%n

filename
filename.2010-01-21.log
filename.2010-01-22.log
filename.2010-01-23.log

/**
 * Measure time elapsed.
 * @author Xuan Ngo
 *
 */
import java.util.Calendar;
import java.util.Date;
import java.text.SimpleDateFormat;
 
public class Chronometer 
{
  private Calendar m_oStart = null;
  private Calendar m_oEnd = null;
 
 
  public Chronometer(){}
 
  public void start()
  {
    this.m_oStart = Calendar.getInstance();
  }
  public void stop()
  {
    this.m_oEnd = Calendar.getInstance();
  }
 
  /**
   * @return Return the elapsed time measured in milliseconds.
   */
  public final long getDiffInMillis()
  {

import org.apache.log4j.Logger;  
 
public class YourClass
{  
  private static final Logger log = Logger.getLogger(YourClass.class)  
  // Some people recommend against making that line static, but Logger.getLogger() is synchronized, so non-static can degrade performance.
 
  public void someMethod() 
  {  
    log.info("Your info message");  

/**
 * Simple Linear Regression: Find a linear function that represents a set of data points.
 * @author Xuan Ngo 
 */
import java.util.ArrayList;
import static java.lang.Math.pow;
import java.lang.RuntimeException;
 
public class SimpleLinearRegression
{
  private ArrayList<Double> m_aX = new ArrayList<Double>();
  private ArrayList<Double> m_aY = new ArrayList<Double>();
 
  private ArrayList<Double> m_aXX = null;
  private ArrayList<Double> m_aXY = null;
 
  private double m_dSumOfXs = 0;
  private double m_dSumOfYs = 0;

-- Slow query: 3.6 seconds
SELECT COUNT(*) FROM sessions WHERE uid = 0 
  AND unix_timestamp() timestamp < (60*15)
 
-- Fast query: 30 milliseconds
SELECT COUNT(*) FROM sessions WHERE uid = 0 
  AND timestamp > (unix_timestamp() (60*15))

/**
 * Convert an octal value to its corresponding ASCII value.
 * Convert from octal(base 8)->decimal(base 10)->character.
 * @author Xuan Ngo
 */
public class OctalToAscii
{
  public static void main(String[] args)
  {
    // Note: octal is base 8.
    String sOctal = "355";
 
    // Convert Octal(base8) to decimal(base 10).
    Integer iOctal = Integer.parseInt(sOctal, 8);
    System.out.println(iOctal); // Output: 237
 
    // Cast decimal to its corresponding ASCII value.
    char cOctal = (char)iOctal.intValue();

/**
 * Examples showing the usages of regular expression in String.replaceAll().
 * @author Xuan Ngo
 */
public class Regex
{
  public static void main(String[] args) 
  {
    String s = "";
 
    /*
     * Remove substring that ends with ,???$
     * Show how to escape and use $.
     */
    s = "53 001,88 $";
    s = s.replaceAll(",...\\$$", "\\$");
    System.out.println(s); // Output: 53 001$
 
    /*
     * Replace a substring regardless of its characters' case(Case Insensitive).
     */
    s = "CaSE Insensitive";