OpenWritings.net

/**
 * Show how to find the degree of a slope.
 * @author Xuan Ngo
 */
public class Trigonometry
{
 
  public static void main(String[] args)
  {
    /**
     * All trigonometric functions in java.lang.Math return values in radians.
     * Therefore, you can use the Math.toDegrees() to convert to degree.
     * The inverse of sin, cosine and tangent are arcsine, arccosine and arctangent.
     */
    double dSlope = 1; // 1=y/x=1/1
    double dRadian = Math.atan(dSlope);
    double dDegree = Math.toDegrees(dRadian);
 

-- Check what indexes are already defined for a table.
SHOW INDEX FROM tablename;
 
-- Create the index.
CREATE INDEX index_name ON tablename(col1, col2, ...);

CREATE TABLE new_table ENGINE=MEMORY AS SELECT * FROM old_table;

SELECT table_schema "Database Name"
     , sum( data_length + index_length ) / 1048576  AS "Database Size in MB"
     , sum( data_free )/ 1048576  AS "Free Space in MB"
FROM information_schema.TABLES
GROUP BY table_schema ;

+--------------------+---------------------+------------------+
| Database Name      | Database Size in MB | Free Space in MB |
+--------------------+---------------------+------------------+
| bt_96580           |              1.1242 |           0.0014 |

import java.awt.Toolkit;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.image.BufferedImage;
 
import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
 
import javax.imageio.ImageIO;
 
/**
 * Take screenshots of the full screen.
 * @author Xuan Ngo
 */
public class PrintScreen
{
  public static void main(String[] args)
  {
    // Print help how to use this application.
    if (args.length != 3)
    {

/**
 * Performance of primitive data type vs object data type.
 * @author Xuan Ngo
 *
 */
public class PrimitiveVsObject
{
  public static void main(String[] args)
  {
    long lStart = 0;
    long lEnd = 0;
    int lMaxSize = 1000000000; // 1 billion.
 
    // Primitive data type

/**
 * Add variable values in a string.
 * @author Xuan Ngo
 *
 */
public class ParamterizedString
{
  public static void main(String[] args)
  {
    String[] aAnimals = new String[]{"horse", "lion", "zebra", "elephant"};
    String s = String.format("The zoo contains: %s, %s, %s, %s.", aAnimals);
    System.out.println(s); // The zoo contains: horse, lion, zebra, elephant.
  }
 
}