Java 5泛型深入研究 泛型——精解
[size=medium][/size] 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,,
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);
}
}

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。

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