Collections以及Arrays

Collections方法:

public static void main(String[] args) {
    
        List<Integer> list = new ArrayList<>();
        list.add(1);
        list.add(2);
        list.add(5);
        list.add(4);

        //sort排序
        System.out.println(list.toString());
        Collections.sort(list);
        System.out.println(list.toString());

       // binarySearch二分查找
       int n =  Collections.binarySearch(list,5);
        System.out.println(n);
     // copy复制
        List<Integer> list2 = new ArrayList<>();
        for (int i=0;i<5;i++){
    
            list2.add(0);
        }
        //该方法要求目标容量必须大于原目标
        Collections.copy(list2,list);
        System.out.println(list2.toString());
      // reserse反转
        Collections.reverse(list);
        System.out.println(list.toString());
       // shuffle 打乱
        Collections.shuffle(list);
        System.out.println(list);
        //list转成数组
        Integer[] arr = list.toArray(new Integer[0]);
        System.out.println(arr.length);
        //数组转集合
        String[] namelist ={
    "ls","he"};
        //受限集合,不能添加和删除
        List<String> list3 = Arrays.asList(namelist);
        System.out.println(list3.toString());
    }

Arrays方法:

public static void main(String[] args) {
    
        int[] arr = {
    1,2,5,6,3};
        //数组排序
// Arrays.sort(arr);
// for (int a:arr
// ) {
    
// System.out.println(a);
// }
        //将数组里面的内容全部打印出来
        System.out.println(Arrays.toString(arr));
        //比较数组元素是否相等
        int[] arr1 = {
    1,2,5,6,3};
        System.out.println(Arrays.equals(arr,arr1));

        //binarysearch 二分查找法找指定元素的索引值
        System.out.println(Arrays.binarySearch(arr,2));
        //截取数组 copeof()
        int n[] = Arrays.copyOf(arr,3);
        System.out.println(Arrays.toString(n));

    }