<T extends Comparable<? super T>> 啥意思啊

public class minStack<T extends Comparable<? super T>> {[br][/br][br][/br]Stack<T> data;[br][/br][br][/br]Stack<T> min;[br][/br][br][/br]T minimum;[br][/br][br][/br]int N;[br][/br][br][/br] [br][/br][br][/br]public minStack() {[br][/br][br][/br]data = new Stack<T>();[br][/br][br][/br]min = new Stack<T>();[br][/br][br][/br]N = 0;[br][/br][br][/br]}