排序

ArrayList<Integer> arrayList = new ArrayList<Integer>();
 arrayList.add(-1);
 arrayList.add(3);
 arrayList.add(3);
 arrayList.add(-5);
 arrayList.add(7);
 arrayList.add(4);
 arrayList.add(-9);
 arrayList.add(-7);
 System.out.println("原始数组:");
 System.out.println(arrayList);
 // void reverse(List list)：反转
 Collections.reverse(arrayList);
 System.out.println("Collections.reverse(arrayList):");
 System.out.println(arrayList);
 // void sort(List list),按⾃然排序的升序排序
 Collections.sort(arrayList);
 System.out.println("Collections.sort(arrayList):");
 System.out.println(arrayList);
 // 定制排序的⽤法
 Collections.sort(arrayList, new Comparator<Integer>() {
 @Override
 public int compare(Integer o1, Integer o2) {
 return o2.compareTo(o1);
 }
 });
 System.out.println("定制排序后：");
 System.out.println(arrayList);

结果
原始数组:
[-1, 3, 3, -5, 7, 4, -9, -7]
Collections.reverse(arrayList):
[-7, -9, 4, 7, -5, 3, 3, -1]
Collections.sort(arrayList):
[-9, -7, -5, -1, 3, 3, 4, 7]
定制排序后：
[7, 4, 3, 3, -1, -5, -7, -9]