📅 最后修改于: 2020-11-15 04:04:44 🧑 作者: Mango
有时您可能想限制允许传递给类型参数的类型的种类。例如，对数字进行操作的方法可能只希望接受Number或其子类的实例。这就是有界类型参数的用途。
要声明一个有界的类型参数，请列出类型参数的名称，然后列出extends关键字，然后列出其上限。
以下示例说明了在一般意义上如何使用扩展来表示“扩展”(如在类中)或“实现”(如在接口中)。这个例子是通用方法，返回三个Comparable对象中的最大对象-
public class MaximumTest {
// determines the largest of three Comparable objects
public static > T maximum(T x, T y, T z) {
T max = x; // assume x is initially the largest
if(y.compareTo(max) > 0) {
max = y; // y is the largest so far
}
if(z.compareTo(max) > 0) {
max = z; // z is the largest now
}
return max; // returns the largest object
}
public static void main(String args[]) {
System.out.printf("Max of %d, %d and %d is %d\n\n",
3, 4, 5, maximum( 3, 4, 5 ));
System.out.printf("Max of %.1f,%.1f and %.1f is %.1f\n\n",
6.6, 8.8, 7.7, maximum( 6.6, 8.8, 7.7 ));
System.out.printf("Max of %s, %s and %s is %s\n","pear",
"apple", "orange", maximum("pear", "apple", "orange"));
}
}
这将产生以下结果-
Max of 3, 4 and 5 is 5
Max of 6.6,8.8 and 7.7 is 8.8
Max of pear, apple and orange is pear