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);
	}

}