public class TestApp {

    public static void main(String[] args) {

        //List-->数组

        List<String> list = new ArrayList<String>();

        list.add("蹇伟");

        list.add("Jerval");

        list.add("杰威");

        Object[] objects = list.toArray();//返回Object数组

        System.out.println("objects:"+Arrays.toString(objects));

        String[] strings1 = new String[list.size()];

        list.toArray(strings1);//将转化后的数组放入已经创建好的对象中

        System.out.println("strings1:"+Arrays.toString(strings1));

        String[] strings2 = list.toArray(new String[0]);//将转化后的数组赋给新对象

        System.out.println("strings2:"+Arrays.toString(strings2));

        //数组-->List

        String[] ss = {"JJ","KK"};

        List<String> list1 = Arrays.asList(ss);

        List<String> list2 = Arrays.asList("AAA","BBB");

        System.out.println(list1);

        System.out.println(list2);

        //List-->Set

        List<String> list3 = new ArrayList<String>(new HashSet<String>());

        //Set-->List

        Set<String> set = new HashSet<String>(new ArrayList<String>());

        //数组-->Set

        String[] strs = {"AA","BB"};

        Set<String> set2 = new HashSet<String>(Arrays.asList(strs));

        System.out.println(set2);

        //Set-->数组

        Set<String> set3 = new HashSet<String>(Arrays.asList("PP","OO"));

        String[] strSet = new String[set3.size()];

        set3.toArray(strSet);

        System.out.println(Arrays.toString(strSet));

        //Map操作

        Map<String, String> map = new HashMap<String, String>();

        map.put("YYY", "UUU");

        map.put("RRR", "TTT");

        // 将键转化为Set

        Set<String> mapKeySet = map.keySet();

        // 将值转化为Set

        Set<String> mapValuesSet = new HashSet<String>(map.values());

        // 将值转化为List

        List<String> mapValuesList = new ArrayList<String>(map.values());

    }

}