A set of new features JDK9

List interface, Set interfaces, Map Interface: which added a static method of, you can add more than one time to a set of elements

Use conditions: when the number stored in the collection of elements has been determined, no change

Note: 1.of method is only applied to the above three interfaces, does not apply to the interface implementation class, class does not implement the method of

　　　The return value is a 2.of method can not change the set , can not use the set of add, put the like to change the elements in the set, an exception is thrown

　　　3.set interfaces and map of the interface when you call the method, you can not have duplicate elements, otherwise it will throw an exception

public static void main(String[] args) {
        List<String> list = List.of("a", "b", "c", "d");
        System.out.println(list);
        // list.add("e"); // java.lang.UnsupportedOperationException

        // Set<String> set = Set.of("a", "b", "b", "c", "d"); // java.lang.IllegalArgumentException
        Set<String> set = Set.of("a", "b", "c", "d");
        System.out.println(set);
        // set.add("e"); // java.lang.An UnsupportedOperationException 

        //the Map <String, Integer> Map.of Map = ( "San", 12, "Wang Wu," 34, "Wang Wu", 18);// java.lang.IllegalArgumentException
        Map<String, Integer> map = Map.of("张三", 12, "李四", 16, "王五", 34);
        System.out.println(map); // java.lang.UnsupportedOperationException
        // map.put("lily", 25); // java.lang.UnsupportedOperationException
        // map.remove("王五"); // java.lang.UnsupportedOperationException
    }