适配器模式Adapter

//Purpose.  Adapter design pattern

//1. Identify the desired interface
//2. Design a "wrapper" class that can "impedance match" the old to the new
//3. The adapter/wrapper class "has a" instance of the legacy class
//4. The adapter/wrapper class "maps" (or delegates) to the legacy object
//5. The client uses (is coupled to) the new interface

class SquarePeg {
	/*** The OLD ***/
	private double width;

	public SquarePeg(double w) {
		width = w;
	}

	public double getWidth() {
		return width;
	}

	public void setWidth(double w) {
		width = w;
	}
}

class RoundHole {
	/*** The NEW ***/
	private int radius;

	public RoundHole(int r) {
		radius = r;
		System.out.println("RoundHole: max SquarePeg is " + r * Math.sqrt(2));
	}

	public int getRadius() {
		return radius;
	}
}

// 2. Design a "wrapper" class that can "impedance match" the old to the new
class SquarePegAdapter {

	// 3. The adapter/wrapper class "has a" instance of the legacy class
	private SquarePeg sp;

	public SquarePegAdapter(double w) {
		sp = new SquarePeg(w);
	}

	// 1. Identify the desired interface
	public void makeFit(RoundHole rh) {
		// 4. The adapter/wrapper class delegates to the legacy object
		double amount = sp.getWidth() - rh.getRadius() * Math.sqrt(2);
		System.out.println("reducing SquarePeg " + sp.getWidth() + " by "
				+ ((amount < 0) ? 0 : amount) + " amount");
		if (amount > 0) {
			sp.setWidth(sp.getWidth() - amount);
			System.out.println("   width is now " + sp.getWidth());
		}
	}
}

public class AdapterDemoSquarePeg {
	public static void main(String[] args) {
		RoundHole rh = new RoundHole(5);
		SquarePegAdapter spa;

		for (int i = 6; i < 10; i++) {
			spa = new SquarePegAdapter((double) i);
			// 5. The client uses (is coupled to) the new interface
			spa.makeFit(rh);
		}
	}
}