Java Basic Learning Note "08" Generics-qualified, generic operation

2. When inheriting the method of implementing an interface, if the generic interface directly specifies the type without subsequent casts, this directly represents the type, and the parameter is the type
4. 1 public static void up (list<? extends number> l) { //method implementation}
6. 1 public Static void down (list<? super number> l) { //method implementation  }
8. Generic Erase

   12	List<Integer> l1 = newArrayList<Integer>();  List l2 = l1;

10. Map cannot traverse the for loop directly because the interface is not implemented
12. List wildcard lsit<?> generally as a method parameter does not indicate what type is not yet known, can receive all the list
14. If you add the same key in the map, overwrite the previous
16. Collections: The tool Class of the collection: it contains the methods of sorting, finding, exchanging elements, and getting synchronized set objects; See API for details;
17. Arrays:

    1	publicstatic<T>List<T> asList(T ... t){}

    returns a fixed-length list set, and a T array element that consists of a list collection element; The returned list collection length cannot be changed, otherwise, an error occurs;

    12345678910111213

    int[] arr = {1,2,3};   List<Integer> l1 = Arrays.asList(arr);//ERROR   List<int[]> l2 = Arrays.asList(arr);//YES     Integer[] arr1 = arr;//ERROR   Integer[] arr1 = {1,2,3};   List<Integer> l3 = Arrays.asList(arr1);     List <----> 数组   List-->数组: Collection接口里的 Object[] toArray();    List l = new ArrayList();      l.add(1);   l.add("a");   l.add(false); Object[] arr= l.toArray();

18. generics: Simple to use (must be mastered):

    123	List list = newArrayList();      String ele = (String)set.get(0);   List<String> list = newArrayList<String>();

    indicates that the set collection can only be loaded as a string type element;

    1	String ele = set.get(0);

    at the bottom are still:
    

    1	String ele = (String)set.get(0);

    123456789

    Map<String,Date> map = new HashMap<String,Date>();     map.put("A",new Date());    Set<Map.Entry<String,Date>> entrys = map.entrySet();   //取出Map里所有Entry对象Iterator<Map.Entry<String,Date>> it = entrys.iterator();//使用迭代器//迭代出每一个Entry对象   while(it.hasNext())    {Map.Entry<String,Date> entry = it.next();     //取出每个entry里的 key和 valueString key = entry.getKey();Date value = entry.getValue();    }  //show(new HashMap<>());

20. Generic method://The declaration placeholder for a generic method can only be placed in front of the method return type;

    1	publicstatic<T> List<T> asList(T ... t){     }

    Static methods of arrays change some mutable parameters to list objects
22. get classname permissions named class bytes static method for code object   class

    1	static class<?> forname (String className)

      Represents all types that are indeterminate and can accept all types;   But you can't add elements to it
24. The upper and lower limits of the list<> cannot be used simultaneously
26. The delimiter for a generic file path uses "/" to be compatible with multiple platforms, "\ \" generally only supports Windows
28. Generally using the file file class to create files does not specify the path is the abstract path is the bin directory, the default is created below
    
    
    
    

Java Basic Learning Note "08" Generics-qualified, generic operation