外观模式

    写了一个画曲线的Swing面板，

public class Test extends JPanel {

	protected void paintComponent(Graphics g) {
		super.paintComponent(g);

		// 画图像
		int nPoint = 201;
		double w = this.getWidth();
		double h = this.getHeight();
		int[] x = new int[nPoint];
		int[] y = new int[nPoint];

		for (int i = 0; i < nPoint; i++) {
			double t = ((double) i) / (nPoint - 1);
			x[i] = (int) (t * w);
			y[i] = (int) (2 * t * h);

		}
		g.drawPolygon(x, y, nPoint);
	}

	public static void main(String[] args) {
		Test t = new Test();
		JFrame f = new JFrame("Test");
		f.getContentPane().add(t);
		f.setLocation(200, 200);
		f.setSize(300, 300);
		f.setVisible(true);
	}
}

    虽然功能是实现了，但是并不怎么好，现在画的是Y=2X, 如果哪天我想画成Y=X*X，那么我必须修改原来的代码，这是比较麻烦的。我们尝试把可变的部分分离出来：

    我们可以看到drawPolygon()方法就只有三个参数，其中两个int数组中存储的数据是画图的关键，那么我们可以把int数组填充数据的方式单独提取出来。

public class PaintPath {
	private double w;
	private double h;

	public PaintPath(double w, double h) {
		this.w = w;
		this.h = h;
	}

	public int[] getX(int nPoint) {
		int[] x = new int[nPoint];
		for (int i = 0; i < nPoint; i++) {
			double t = ((double) i) / (nPoint - 1);
			x[i] = (int) (t * w);

		}
		return x;
	}
	
	public int[] getY(int nPoint) {
		int[] x = new int[nPoint];
		for (int i = 0; i < nPoint; i++) {
			double t = ((double) i) / (nPoint - 1);
			x[i] = (int) (2 * t * h);

		}
		return x;
	}

}

public class Test extends JPanel {

	protected void paintComponent(Graphics g) {
		super.paintComponent(g);

		// 画图像
		int nPoint = 201;
		double w = this.getWidth();
		double h = this.getHeight();

		PaintPath p = new PaintPath(w, h);
		g.drawPolygon(p.getX(nPoint), p.getY(nPoint), nPoint);

	}

	public static void main(String[] args) {
		Test t = new Test();
		JFrame f = new JFrame("Test");
		f.getContentPane().add(t);
		f.setLocation(200, 200);
		f.setSize(300, 300);
		f.setVisible(true);
	}
}