Java 泛型学习(Java 泛型的理解与等价实现)02

三、泛型的综合运用实例（代码参考java参考大全，有改动）

public class AvgGen<T extends Number> {
  public AvgGen() {
  }

  public double getAvg(T[] arr) {
    double sum = 0.0;
    for (int i = 0; i < arr.length; i++) {
      sum = sum + arr[i].doubleValue();
    }
    return sum / arr.length;
  }

  public static void main(String[] args) {
    // 整形数组求均值
    System.out.println("整形数组{1, 3}求均值:");
    Integer[] intArr = { 1, 3 };
    AvgGen<Integer> intObj = new AvgGen<Integer>();
    double intavg = intObj.getAvg(intArr);
    System.out.println(intavg);
    System.out.println();
    // 浮点型数组求均值
    System.out.println("浮点型数组{1.1f,2.9f}求均值:");
    Float[] fArr = { 1.1f, 2.9f };
    AvgGen<Float> fObj = new AvgGen<Float>();
    double favg = fObj.getAvg(fArr);
    System.out.println(favg);
  }
}

/**
 * Created by IntelliJ IDEA. User: leizhimin Date: 2007-9-18 Time: 11:08:14 使用通配符泛型参数：泛型参数是可变的，可在运行时来确定。
 */
public class AvgCompGen<T extends Number> {
  private T[] arr;

  /**
   * 构造函数
   *
   * @param arr
   */
  public AvgCompGen(T[] arr) {
    this.arr = arr;
  }

  /**
   * 求数组均值
   *
   * @return 数组均值
   */
  public double getAvg() {
    double sum = 0.0;
    for (int i = 0; i < arr.length; i++) {
      sum += arr[i].doubleValue();
    }
    return sum / arr.length;
  }

  /**
   * 比较数组均值是否相等(使用通配符泛型参数) AvgCompGen<?>表示可以匹配任意的AvgCompGen对象，有点类似Object
   *
   * @param x 目标对象
   * @return 均值是否相等
   */
  public boolean sameAvg(AvgCompGen<?> x) {
    if (getAvg() == x.getAvg())
      return true;
    return false;
  }

  /**
   * 主函数：用来测试
   *
   * @param args
   */
  public static void main(String[] args) {
    // 创建参数为Integer类型泛型对象
    Integer[] intArr = { 1, 3 };
    AvgCompGen<Integer> intObj = new AvgCompGen<Integer>(intArr);
    System.out.println("intObj的平均值=" + intObj.getAvg());
    // 创建参数为Double类型泛型对象
    Double[] douArr = { 1.0, 3.0 };
    AvgCompGen<Double> douObj = new AvgCompGen<Double>(douArr);
    System.out.println("douObj的平均值=" + douObj.getAvg());
    // 创建参数为Float类型泛型对象
    Float[] fltArr = { 0.8f, 3.2f };
    AvgCompGen<Float> fltObj = new AvgCompGen<Float>(fltArr);
    System.out.println("fltObj的平均值=" + fltObj.getAvg());
    // 两两比较对象的均值是否相等
    if (intObj.sameAvg(douObj))
      System.out.println("intArr与douArr的值相等,结果为:" + " intObj的均值=" + intObj.getAvg()
          + "   douObj的均值=" + douObj.getAvg());
    else
      System.out.println("intArr与douArr的值不相等,结果为:" + " intObj的均值=" + intObj.getAvg()
          + "   douObj的均值=" + douObj.getAvg());
    if (intObj.sameAvg(fltObj))
      System.out.println("intArr与fltObj的值相等,结果为:" + " intObj的均值=" + intObj.getAvg()
          + "   fltObj的均值=" + fltObj.getAvg());
    else
      System.out.println("intArr与fltObj的值不相等,结果为:" + " intObj的均值=" + intObj.getAvg()
          + "   fltObj的均值=" + fltObj.getAvg());
    if (douObj.sameAvg(fltObj))
      System.out.println("douObj与fltObj的值相等,结果为:" + " douObj的均值=" + intObj.getAvg()
          + "   fltObj的均值=" + fltObj.getAvg());
    else
      System.out.println("douObj与fltObj的值不相等,结果为:" + " douObj的均值=" + intObj.getAvg()
          + "   fltObj的均值=" + fltObj.getAvg());
  }
}

/**
 * Created by IntelliJ IDEA. User: leizhimin Date: 2007-9-18 Time: 16:09:37 三种坐标，用泛型实现坐标打印
 */
public class TwoD {
  int x, y;

  public TwoD(int x, int y) {
    this.x = x;
    this.y = y;
  }
}

class ThreeD extends TwoD {
  int z;

  public ThreeD(int x, int y, int z) {
    super(x, y);
    this.z = z;
  }
}

class FourD extends ThreeD {
  int t;

  public FourD(int x, int y, int z, int t) {
    super(x, y, z);
    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) {
    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 + "  "
          + 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);
  }
}

public class AvgGen<T extends Number> {
  public AvgGen() {
  }

  public double getAvg(T[] arr) {
    double sum = 0.0;
    for (int i = 0; i < arr.length; i++) {
      sum = sum + arr[i].doubleValue();
    }
    return sum / arr.length;
  }

  public static void main(String[] args) {
    // 整形数组求均值
    System.out.println("整形数组{1, 3}求均值:");
    Integer[] intArr = { 1, 3 };
    AvgGen<Integer> intObj = new AvgGen<Integer>();
    double intavg = intObj.getAvg(intArr);
    System.out.println(intavg);
    System.out.println();
    // 浮点型数组求均值
    System.out.println("浮点型数组{1.1f,2.9f}求均值:");
    Float[] fArr = { 1.1f, 2.9f };
    AvgGen<Float> fObj = new AvgGen<Float>();
    double favg = fObj.getAvg(fArr);
    System.out.println(favg);
  }
}

/**
 * Created by IntelliJ IDEA. User: leizhimin Date: 2007-9-18 Time: 11:08:14 使用通配符泛型参数：泛型参数是可变的，可在运行时来确定。
 */
public class AvgCompGen<T extends Number> {
  private T[] arr;

  /**
   * 构造函数
   * 
   * @param arr
   */
  public AvgCompGen(T[] arr) {
    this.arr = arr;
  }

  /**
   * 求数组均值
   * 
   * @return 数组均值
   */
  public double getAvg() {
    double sum = 0.0;
    for (int i = 0; i < arr.length; i++) {
      sum += arr[i].doubleValue();
    }
    return sum / arr.length;
  }

  /**
   * 比较数组均值是否相等(使用通配符泛型参数) AvgCompGen<?>表示可以匹配任意的AvgCompGen对象，有点类似Object
   * 
   * @param x 目标对象
   * @return 均值是否相等
   */
  public boolean sameAvg(AvgCompGen<?> x) {
    if (getAvg() == x.getAvg())
      return true;
    return false;
  }

  /**
   * 主函数：用来测试
   * 
   * @param args
   */
  public static void main(String[] args) {
    // 创建参数为Integer类型泛型对象
    Integer[] intArr = { 1, 3 };
    AvgCompGen<Integer> intObj = new AvgCompGen<Integer>(intArr);
    System.out.println("intObj的平均值=" + intObj.getAvg());
    // 创建参数为Double类型泛型对象
    Double[] douArr = { 1.0, 3.0 };
    AvgCompGen<Double> douObj = new AvgCompGen<Double>(douArr);
    System.out.println("douObj的平均值=" + douObj.getAvg());
    // 创建参数为Float类型泛型对象
    Float[] fltArr = { 0.8f, 3.2f };
    AvgCompGen<Float> fltObj = new AvgCompGen<Float>(fltArr);
    System.out.println("fltObj的平均值=" + fltObj.getAvg());
    // 两两比较对象的均值是否相等
    if (intObj.sameAvg(douObj))
      System.out.println("intArr与douArr的值相等,结果为:" + " intObj的均值=" + intObj.getAvg()
          + "   douObj的均值=" + douObj.getAvg());
    else
      System.out.println("intArr与douArr的值不相等,结果为:" + " intObj的均值=" + intObj.getAvg()
          + "   douObj的均值=" + douObj.getAvg());
    if (intObj.sameAvg(fltObj))
      System.out.println("intArr与fltObj的值相等,结果为:" + " intObj的均值=" + intObj.getAvg()
          + "   fltObj的均值=" + fltObj.getAvg());
    else
      System.out.println("intArr与fltObj的值不相等,结果为:" + " intObj的均值=" + intObj.getAvg()
          + "   fltObj的均值=" + fltObj.getAvg());
    if (douObj.sameAvg(fltObj))
      System.out.println("douObj与fltObj的值相等,结果为:" + " douObj的均值=" + intObj.getAvg()
          + "   fltObj的均值=" + fltObj.getAvg());
    else
      System.out.println("douObj与fltObj的值不相等,结果为:" + " douObj的均值=" + intObj.getAvg()
          + "   fltObj的均值=" + fltObj.getAvg());
  }
}

/**
 * Created by IntelliJ IDEA. User: leizhimin Date: 2007-9-18 Time: 16:09:37 三种坐标，用泛型实现坐标打印
 */
public class TwoD {
  int x, y;

  public TwoD(int x, int y) {
    this.x = x;
    this.y = y;
  }
}

class ThreeD extends TwoD {
  int z;

  public ThreeD(int x, int y, int z) {
    super(x, y);
    this.z = z;
  }
}

class FourD extends ThreeD {
  int t;

  public FourD(int x, int y, int z, int t) {
    super(x, y, z);
    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) {
    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 + "  "
          + 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);
  }
}

原文请见： http://www.java2000.net/p7927

                 http://www.java2000.net/p7926

注意：多个泛型类、接口，接口、类继承，这种设计方式往往会导致泛型很复杂，程序的可读性急剧下降，程序中应该兼顾代码的可读性。

总结：
泛型其实就是一个类型的参数化，没有它程序照样写！把这句话记心里。有两层含义：一是泛型的实质，二是要知其然还要知其所以然。泛型不可怕，泛型的设计也从开发者角度出发的，使用得当会大大提高代码的安全性和简洁性。