ADAPTER（适配器） --- 类对象结构型模式

1、意图
    将一个类的接口转化成客户希望的另外一个接口。Adapter模式使得原本由于接口不兼容而不能一起工作的那些类可以一起工作。
2、别名
    包装类  Wrapper
3、动机
   有时，为复用而设计的工具类不能被复用的原因仅仅是因为它的接口与专业应用领域所需要的接口不匹配。
4、适用性
  以下情况使用Adapter模式
    你想使用一个已经存在的类，而它的接口不符合你的需求
    你想创建一个可以复用的类，该类可以与其它不相关的类或不可预见的类（即那些接口可能不一定兼容的类）协同工作
   （仅适用于对象Adapter）你想使用一些已经存在的子类，但是不可能对每一个都进行子类化以匹配它们的接口。对象适配器可以适配它的父亲接口。
5、结构
  类适配器使用多重继承对一个接口与另外一个接口进行匹配，如下图所示


  对象匹配器依赖于对象组合，如下图所示


6、代码实例

Before

Because the interface between Line and Rectangle objects is incapatible, the user has to recover the type of each shape and manually supply the correct arguments.

class LegacyLine
{
    public void draw(int x1, int y1, int x2, int y2)
    {
        System.out.println("line from (" + x1 + ',' + y1 + ") to (" + x2 + ',' 
          + y2 + ')');
    }
}

class LegacyRectangle
{
    public void draw(int x, int y, int w, int h)
    {
        System.out.println("rectangle at (" + x + ',' + y + ") with width " + w
          + " and height " + h);
    }
}

public class AdapterDemo
{
    public static void main(String[] args)
    {
        Object[] shapes = 
        {
            new LegacyLine(), new LegacyRectangle()
        };
        // A begin and end point from a graphical editor
        int x1 = 10, y1 = 20;
        int x2 = 30, y2 = 60;
        for (int i = 0; i < shapes.length; ++i)
          if (shapes[i].getClass().getName().equals("LegacyLine"))
            ((LegacyLine)shapes[i]).draw(x1, y1, x2, y2);
          else if (shapes[i].getClass().getName().equals("LegacyRectangle"))
            ((LegacyRectangle)shapes[i]).draw(Math.min(x1, x2), Math.min(y1, y2)
              , Math.abs(x2 - x1), Math.abs(y2 - y1));
    }
}

line from (10,20) to (30,60) rectangle at (10,20) with width 20 and height 40

After

The Adapter’s “extra level of indirection” takes care of mapping a user-friendly common interface to legacy-specific peculiar interfaces.

class LegacyLine
{
    public void draw(int x1, int y1, int x2, int y2)
    {
        System.out.println("line from (" + x1 + ',' + y1 + ") to (" + x2 + ',' 
          + y2 + ')');
    }
}

class LegacyRectangle
{
    public void draw(int x, int y, int w, int h)
    {
        System.out.println("rectangle at (" + x + ',' + y + ") with width " + w
          + " and height " + h);
    }
}

interface Shape
{
  void draw(int x1, int y1, int x2, int y2);
}

class Line implements Shape
{
    private LegacyLine adaptee = new LegacyLine();
    public void draw(int x1, int y1, int x2, int y2)
    {
        adaptee.draw(x1, y1, x2, y2);
    }
}

class Rectangle implements Shape
{
    private LegacyRectangle adaptee = new LegacyRectangle();
    public void draw(int x1, int y1, int x2, int y2)
    {
        adaptee.draw(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1),
          Math.abs(y2 - y1));
    }
}

public class AdapterDemo
{
    public static void main(String[] args)
    {
        Shape[] shapes = 
        {
            new Line(), new Rectangle()
        };
        // A begin and end point from a graphical editor
        int x1 = 10, y1 = 20;
        int x2 = 30, y2 = 60;
        for (int i = 0; i < shapes.length; ++i)
          shapes[i].draw(x1, y1, x2, y2);
    }
}

line from (10,20) to (30,60) rectangle at (10,20) with width 20 and height 40