外观模式Facade

//Purpose.  Facade design pattern

//1. Identify the desired unified interface for a set of subsystems
//2. Design a "wrapper" class that can encapsulate the use of the subsystems
//3. The client uses (is coupled to) the Facade
//4. The facade/wrapper "maps" to the APIs of the subsystems

class PointCarte {                           // 1. Subsystem
private double x, y;
public PointCarte( double xx, double yy ) { x = xx;   y = yy; }
public void   move( int dx, int dy )      { x += dx;  y += dy; }
public String toString()                  { return "(" + x + "," + y + ")"; }
public double getX() { return x; }        public double getY() { return y; } 
}

class PointPolar {                           // 1. Subsystem
private double radius, angle;
public PointPolar( double r, double a )   { radius = r;  angle = a; }
public void   rotate( int ang )           { angle += ang % 360; }
public String toString()         { return "[" + radius + "@" + angle + "]"; }
}

class Point {                                // 1. Desired i/f: move(), rotate()
private PointCarte pc;                    // 2. Design a "wrapper" class
public Point( double xx, double yy ) { pc = new PointCarte( xx,yy ); }
public String toString()             { return pc.toString(); }
public void move( int dx, int dy )   { pc.move( dx,dy ); } // 4. Wrapper maps
public void rotate( int angle, Point o ) {
   double x = pc.getX() - o.pc.getX(), y = pc.getY() - o.pc.getY();
   PointPolar pp = new PointPolar( Math.sqrt(x*x+y*y),
                                   Math.atan2(y,x)*180/Math.PI );
   pp.rotate( angle );                                     // 4. Wrapper maps
   System.out.println( "   PointPolar is " + pp );
   String str = pp.toString();  int i = str.indexOf( '@' );
   double r = Double.parseDouble( str.substring(1,i) );
   double a = Double.parseDouble( str.substring(i+1,str.length()-1) );
   pc = new PointCarte(r*Math.cos(a*Math.PI/180) + o.pc.getX(),
                       r*Math.sin(a*Math.PI/180) + o.pc.getY() );
}  }

class Line {
private Point o, e;
public Line( Point ori, Point end )  { o = ori;  e = end; }
public void   move( int dx, int dy ) { o.move( dx, dy );  e.move( dx, dy ); }
public void   rotate( int angle )    { e.rotate( angle, o ); }
public String toString()       { return "origin is " + o + ", end is " + e; }
}

public class FacadeDemo {
public static void main( String[] args ) {
   Line line1 = new Line( new Point(2,4), new Point(5,7) );  // 3. Client
   line1.move(-2,-4);                                        //    uses the
   System.out.println( "after move:   " + line1 );           //    Facade
   line1.rotate(45);
   System.out.println( "after rotate: " + line1 );
   Line line2 = new Line( new Point(2,1), new Point(2.866,1.5) );
   line2.rotate(30);
   System.out.println( "30 degrees to 60 degrees: " + line2 );
}  }