java泛型

package e_10_09;

/** 
 * 三种坐标，用泛型实现坐标打印 
 */ 
class TwoD {//二维坐标
  int x, y;  
  public TwoD(int x, int y) {  
    this.x = x;  
    this.y = y;  
  }  
}  
 
class ThreeD extends TwoD {//三维坐标
  int z;  
 
  public ThreeD(int x, int y, int z) {  
    super(x, y);//必须写在第一行  
    this.z = z;  
  }  
}  
 
class FourD extends ThreeD {//四维坐标
  int t;  
 
  public FourD(int x, int y, int z, int t) {  
    super(x, y, z);//必须写在子类的第一行  
    this.t = t;  
  }  
}  
 
/** 
 * 存放泛型坐标的（数据结构）类 
 */ 
class Coords<T extends TwoD> {  
  T[] coords;  
 
  public Coords(T[] coords) {  
    this.coords = coords;  
  }  
}  
 
/** 
 * 工具类--打印泛型数据 并给出一个测试方法 
 */ 
class BoundeWildcard {  
  static void showXY(Coords<?> c) {  
    System.out.println("X Y Coordinates:");  
    for (int i = 0; i < c.coords.length; i++) {  
      System.out.println(c.coords[i].x + "  " + c.coords[i].y);  
    }  
    System.out.println();  
  }  
 
  static void showXYZ(Coords<? extends ThreeD> c) {  
    System.out.println("X Y Z Coordinates:");  
    for (int i = 0; i < c.coords.length; i++) {  
      System.out.println(c.coords[i].x + "  " + c.coords[i].y + "  " + c.coords[i].z);  
    }  
    System.out.println();  
  }  
 
  static void showAll(Coords<? extends FourD> c) {   
        for (int i = 0; i < c.coords.length; i++) {  
      System.out.println(c.coords[i].x + "  " + c.coords[i].y + "  " + c.coords[i].z + "  " 
          + c.coords[i].t);  
    }  
    System.out.println();  
  }  
 
  public static void main(String args[]) {  
    TwoD td[] = { new TwoD(0, 0), new TwoD(7, 9), new TwoD(18, 4), new TwoD(-1, -23) };  
    Coords<TwoD> tdlocs = new Coords<TwoD>(td);  
    System.out.println("Contents of tdlocs.");  
    showXY(tdlocs);  
    FourD fd[] = { new FourD(1, 2, 3, 4), new FourD(6, 8, 14, 8), new FourD(22, 9, 4, 9),  
        new FourD(3, -2, -23, 17) };  
    Coords<FourD> fdlocs = new Coords<FourD>(fd);  
    System.out.println("Contents of fdlocs.");  
    showXY(fdlocs);  
    showXYZ(fdlocs);  
    showAll(fdlocs);  
  }  
}