// This class defines a blueprint for PositivePoint objects.
// PositivePoint have an x and y value that are never negative.
//
// If something happens that would set the x or y value to a 
// negative number, it gets set to 0 instead.
// 
// PositivePoints have methods for translating, finding the 
// distance to the origin and converting to Strings.
public class PositivePoint {
   //fields: data / information
   
   // These fields are private so that no client can change them directly
   private int x;
   private int y;
   
   //Constructors:
   public PositivePoint(int x, int y){
      //since the arguments and fields have the same name, Java could
      // get confused, so "x" refers to the argument and "this.x" refers
      // to the field.
      this.x = x;
      this.y = y;
      // fix x and y if either were set to a negative value
      guaranteePositive();
   }
   
   public PositivePoint(){
      this.x = 0;
      this.y = 0;
   }
   
   //instance methods: behavoir / actions
   
   // Translates this point by the given dx and dy
   public void translate(int dx, int dy) {
      this.x += dx;
      this.y += dy;
      // fix x and y if either were set to a negative value
      guaranteePositive();
   }
   
   // Returns this Point's distance from origin
   public double distanceFromOrigin() {
      return Math.sqrt(x * x + y * y);
   }
   
   // Returns the String representation of this Point.
   public String toString(){
      return this.x + ", " + this.y;
   }
   
   // This is an internal helper method to make sure the x and y values
   // never end up negative.
   // It labeled "private" since no one outside the object needs it, but
   // it would still work if it were labeled "public".
   private void guaranteePositive(){
      if(this.x < 0) {
         this.x = 0;
      }
      if(this.y < 0) {
         this.y = 0;
      }
   }
}