泛型

Collections类
1.extends
X是X的子类
2.super
X是X的父类

public static <T extends Comparable<? super T>> void sort(List<T> list) {

Object[] a = list.toArray(); Arrays.sort(a); ListIterator<T> i = list.listIterator(); for (int j=0; j<a.length; j++) {     i.next();     i.set((T)a[j]); } } 

public static <T extends Comparable<? super T>> void sort(List<T> list) {

Object[] a = list.toArray(); Arrays.sort(a); ListIterator<T> i = list.listIterator(); for (int j=0; j<a.length; j++) {     i.next();     i.set((T)a[j]); } }   

测试类

Student没有实现比较接口Comparable，编译器报错。

代码
package sort;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class ArrayListtest {

public static void main(String[] args) {     List<Student> a = new ArrayList<Student>();     Collections.sort(a); } 

}