Scala Days 2013

Videos of Scala Days 2013 (http://scaladays.org/) on Parleys:

http://www.parleys.com/channel/51ae1022e4b01033a7e4b6ca

MOOC: Introduction to Programming (Java)

Learn programming with Java from Cay Horstmann, Cheng-Han Lee and Sara Tansey of the San José State University in the MOOC at Udacity:

"Introduction to Programming (Java)"

starting Jun 3rd 2013.

OOP Tutorial: 2-dimensional Vector as Scala Object

As before in Java: When starting to learn object orientated programming, a good first example is the following: Modelling a 2-dimensional vector over the real numbers could result in this (pay attention to the overloading of * and +. Compare to the verbose Java variant):

package de.bigdev

class Vector(val x: Double, val y: Double) {
    
  /**
   * Addition of two vectors
   *
   * @param v
   * @return the sum with v
   */
  def +(v: Vector) = new Vector(x + v.x, y + v.y)
  
  /**
   * Scalar Mulitplication with a constant
   *
   * @param c
   * @return the scalar multiplication with c
   */
  def *(c: Double) = new Vector(c * x, c * y)

  /**
   * Length of two vectors
   *
   * @return length
   */
  def length = math.sqrt(x * x + y * y)

  /**
   * Scalar Product of two vectors
   *
   * @param v
   * @return the scalar product with v
   */
  def *(v: Vector) = x * v.x + y * v.y
  
  /**
   * Angle between two vectors
   *
   * @param v
   * @return the angle with v in degrees
   */
  def angle(v: Vector) = math.acos(this * v / (this.length * v.length)) *
    180.0 / Math.PI

  override def toString = "[" + x + "," + y + "]"
}

For execution we need a main method (pay attention to the usage of *, + and angle):

package de.bigdev

object VectorTest {

  /**
   * for testing only... or use ScalaTest!
   */
  def main(args: Array[String]) {

    val v = new Vector(1, 1)
    val w = new Vector(-1, -1)

    println("Vector algebra")
    println("==============")
    println("addition      : " + v + " + " + w + " = " + (v + w))
    println("scalar multip.: 2 * " + v + " = " + v * 2)
    println("length        : ||" +v + "|| = " + v.length)
    println("scalar product: " + v + " * " + w + " = " + v * w)
    println("angle         : angle(" + v + ", " + w
      + ") = " + math.round(v angle w) + "°")
  }
}

The output on the console is:

Vector algebra
==============
addition      : [1.0,1.0] + [-1.0,-1.0] = [0.0,0.0]
scalar multip.: 2 * [1.0,1.0] = [2.0,2.0]
length        : ||[1.0,1.0]|| = 1.4142135623730951
scalar product: [1.0,1.0] * [-1.0,-1.0] = -2.0
angle         : angle([1.0,1.0], [-1.0,-1.0]) = 180°

OOP Tutorial: 2-dimensional Vector as Java Object

When starting to learn object orientated programming, a good first example is the following: Modelling a 2-dimensional vector over the real numbers could result in this

package de.bigdev;

public class Vector {

    private double x;
    private double y;

    public Vector(double x, double y) {
        super();
        this.x = x;
        this.y = y;
    }
    
    /**
     * Addition of two vectors
     *
     * @param v
     * @return the sum with v
     */
    public Vector add(Vector v) {
        return new Vector(x + v.x, y + v.y);
    }
    
    /**
     * Scalar Mulitplication with a constant
     *
     * @param c
     * @return the scalar multiplication with c
     */
    public Vector scalarMult(double c) {
        return new Vector(c * x, c * y);
    }

    /**
     * Length of two vectors
     * 
     * @return length
     */
    public double length() {
        return Math.sqrt(x * x + y * y);
    }

    /**
     * Scalar Product of two vectors
     * 
     * @param v
     * @return the scalar product with v
     */
    public double scalarProd(Vector v) {
        return this.x * v.getX() + this.y * v.getY();
    }

    /**
     * Angle between two vectors
     * 
     * @param v
     * @return the angle with v in degrees
     */
    public double angle(Vector v) {
        return Math.acos(this.scalarProd(v) / (this.length() * v.length()))
                * 180.0 / Math.PI;
    }

    public double getX() { return x; }
    public double getY() { return y; }

    @Override
    public String toString() {
        return "[" + x + ", " + y + "]";
    }

    /**
     * for testing only. should be factored out into another class... or use
     * JUnit!
     * 
     * @param args
     */
    public static void main(String[] args) {
        Vector v = new Vector(1, 1);
        Vector w = new Vector(-1, -1);

        System.out.println("Vector algebra");
        System.out.println("==============");
        System.out.println("addition      : " + v + " + " + w + " = " + v.add(w));
        System.out.println("scalar multip.: 2 * " + v + " = " + v.scalarMult(2));
        System.out.println("length        : ||" +v + "|| = " + v.length());
        System.out.println("scalar product: " + v + " * " + w + " = " + v.scalarProd(w));
        System.out.println("angle         : angle(" + v + ", " + w
          + ") = " + Math.round(v.angle(w)) + "°");
    }
}

The output on the console is


Vector algebra
==============
addition      : [1.0, 1.0] + [-1.0, -1.0] = [0.0, 0.0]
scalar multip.: 2 * [1.0, 1.0] = [2.0, 2.0]
length        : ||[1.0, 1.0]|| = 1.4142135623730951
scalar product: [1.0, 1.0] * [-1.0, -1.0] = -2.0
angle         : angle([1.0, 1.0], [-1.0, -1.0]) = 180°