/*
   Point: 
     a class whose objects represent 2d points
 */

class Point extends Object
{
  private double x;
  private double y;

  // method: two-argument constructor
  //     in: two doubles, x and y
  //    out: a new Point
  public Point(double x_in, double y_in)
  {
    this.x = x_in;
    this.y = y_in;
  }

  // method: zero-argument constructor
  //     in: no inputs
  //    out: a new Point (at the origin)
  public Point() // a zero-input constructor!
  {
    this.x = 0.0;
    this.y = 0.0;
  }

  // method: nudgeBy
  //     in: two doubles, the amount to nudge the point
  //    out: nothing (a void function)
  //  ** But, this point itself has changed **
  public void nudgeBy(double delta_x, double delta_y)
  {
    this.x = this.x + delta_x;
    this.y += delta_y;         // shorter way
    return;
  }

  // method: equals
  //     in: a Point, other
  //    out: a boolean, whether or not this and p are at
  //         the same coordinates.the same Point
  public boolean equals(Point other)
  {
    if ( this.x == other.x  &&  this.y == other.y ) {
      return true;
    } else {
      return false;
    }
    
    // Alternatively, we could say it in one line:
    //   return ( this.x == other.x  &&  this.y == other.y );
  }

  // method: toString
  //     in: none
  //    out: a String representation of this Point
  public String toString()
  {
    String s = "(" + this.x + "," + this.y + ")";
    return s;
  }  

  // method: magnitude
  //   in: nothing (no arguments)
  //   out: a double, the distance from the origin to 'this'.
  public double magnitude()
  {
    // An example of calling Math (static) methods
    // The Java API lists them all (Google for "Java 1.6 API")
    return Math.sqrt( this.x*this.x + this.y*this.y );
  }

  // static method: add
  //     in: two Points, p1 and p2
  //    out: a new Point that is the sum of p1 and p2
  static public Point add( Point p1, Point p2 )
  {
    return new Point( p1.x + p2.x, p1.y + p2.y );
  }

  // static method: displaySmaller
  //   in: Two points
  //   out: nothing (a void function)
  public static void displaySmaller(Point a, Point b)
  {
    double aMag = a.magnitude();
    double bMag = b.magnitude();
    
    if (aMag < bMag)  {
      System.out.println(a + " is smaller than " + b);
      System.out.println("Smallest magnitude is " + aMag);
    } else {
      System.out.println(a + " is not smaller than " + b);
      System.out.println("Smallest magnitude is " + bMag);
    }
  }
  
  // static method: main
  //     in: any parameters specified with the run command (ignored)
  //    out: nothing (a void function)
  // ** printing stuff is quite different from returning stuff! **
  public static void main(String[] args)
  {
    Point p1 = new Point(30, 40);
    Point p2 = new Point(12,  2);

    System.out.println( "p1 is " + p1.toString() );
    System.out.println( "p2 is " + p2 );

    p1.nudgeBy( 30, 20 );
    System.out.println("now p1 is " + p1);

    Point p3 = Point.add( p1, p2 );
    System.out.println( "p3 (their sum) is " + p3 );

    Point.displaySmaller(p1, p2);
    
    Point p4 = new Point();
    p4.nudgeBy( 60, 60 );
    
    System.out.println("p1 == p4 is " + (p1 == p4) );
    System.out.println("p1.equals(p4) is " + p1.equals(p4));
    
    Point p5 = p2;
    System.out.println("Before nudge:");
    System.out.println("p2 is " + p2);
    System.out.println("p5 is " + p5);
 
    p2.nudgeBy(5, 5);
    
    System.out.println("After nudge:");
    System.out.println("p2 is " + p2);
    System.out.println("p5 is " + p5);
    System.out.println("p2 == p5 is " + (p2 == p5) );
    
    return;
  }

}