Collection工具类

/**
 * Collections工具类使用
 */
public class Demo03 {
    public static void main(String[] args) {

        List<Integer> list = new ArrayList<Integer>();
        list.add(20);
        list.add(5);
        list.add(8);
        list.add(15);
        //sort排序
        System.out.println("排序前:"+list.toString());
        Collections.sort(list);//默认从小到大
        System.out.println("排序后:"+list.toString());

        //二分查找
        int i = Collections.binarySearch(list,15);//二分查找需要先进行排序，找到返回下标
        System.out.println(i);

        //copy
        List<Integer> list1 = new ArrayList<Integer>();
        for(int k=0; k<list.size();k++){
            list1.add(0);
        }
        Collections.copy(list1,list);
        System.out.println("copy:"+list1.toString());//复制，需要先使dest和src大小相同

        //reverse反转
        Collections.reverse(list);
        System.out.println("reverse:"+list);

        //shuffle 打乱
        Collections.shuffle(list);
        System.out.println("Shuffle:"+list);

        //补充：list转为数组
        System.out.println("list转为数组");
        Integer[] arr = list.toArray(new Integer[0]);
        System.out.println(Arrays.toString(arr));

        //数组转为list
        System.out.println("数组转为list");
        String[] names = {"A","B","C","D"};
        //集合是一个受限集合，不能添加和删除
        List<String> list2 = Arrays.asList(names);
        System.out.println(list2.toString());

        //把基本类型数组转成集合时，需要修改为包装类型（基本类型对应的引用类型）
        Integer[] nums = {100,200,300,400,500};
        List<Integer> list3 = Arrays.asList(nums);
        System.out.println(list3);

    }
}