Generic Methods and Bounded Type Parameters泛型方法和有界类型参数

Bounded type parameters are key to the implementation of generic algorithms. 有界类型参数是实现泛型算法的关键。Consider the following method that counts the number of elements in an array T[] that are greater than a specified element elem.考虑下面的方法，它计算数组T[]中元素大于指定元素elm的数目。

public static <T> int countGreaterThan(T[] anArray, T elem) {
    int count = 0;
    for (T e : anArray)
        if (e > elem)  // compiler error
            ++count;
    return count;
}

The implementation of the method is straightforward, but it does not compile because the greater than operator (>) applies only to primitive types such as short, int, double, long, float, byte, and char. 该方法的实现非常简单，但由于使用了大于运算符（>），因此无法编译仅适用于基本类型，如short、int、double、long、float、byte和char。You cannot use the > operator to compare objects. 您不能使用>运算符来比较对象。To fix the problem, use a type parameter bounded by the Comparable<T> interface:要解决此问题，请使用由Comparable<T>接口限定的类型参数：

public interface Comparable<T> {
    public int compareTo(T o);
}

The resulting code will be:生成的代码将是：

public static <T extends Comparable<T>> int countGreaterThan(T[] anArray, T elem) {
    int count = 0;
    for (T e : anArray)
        if (e.compareTo(elem) > 0)
            ++count;
    return count;
}