集合框架 Map之HashMap

Map 接口定义 : 将键映射到值的对象。一个映射不能包含重复的键；每个键最多只能映射一个值。

 

          HashMap是Map接口的实现类，实现键到值的映射的哈希表。通过键来查找相对应的值。

 

           用法 ：

            Map 对象名  = new HashMap（）；

     

           HashMap的常用方法 ： put（object key ，ovbject value）; keySet（）；values（）；

                                               get（object key）； remove（object key）；

 

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           public Map findBoard() {

                 Map map = new HashMap();

                 List boardList = new ArrayList();

                 List sunBoardList1 = new ArrayList();

                 List sunBoardList2 = new ArrayList();

 

                 for (int i = 0; i < 2; i++) {

                        BoardBean board = new BoardBean();

                        board.setBoardId(i + 1);

                        board.setBoardTitle("主版块" + i);

                        board.setParentId(0);

                        boardList.add(board);

                 }

                 map.put("0", boardList);

 

                 for (int i = 0; i < 2; i++) {

                       BoardBean board = new BoardBean();

                       board.setBoardId(i + 1);

                       board.setBoardTitle("主版块为1的子版块Id：" + i);

                       board.setParentId(i);

                       sunBoardList1.add(board);

                 }

                 map.put("1", sunBoardList1);

  

                 for (int i = 0; i < 2; i++) {

                       BoardBean board = new BoardBean();

                       board.setBoardId(i + 1);

                       board.setBoardTitle("组板块为2的子版块Id：" + i);

                       board.setParentId(2);

                       sunBoardList2.add(board);

                 }

                 map.put("2", sunBoardList2);

           

                return map;

         }

 

 

 

         public class BoardDaoImplTest {

        

                public static void main(String [] args){

                      BoardDao boardDao = new BoardDao ();

                      Map mapBoard = boardDao.findBoard ();

                      List boardList  = (List) mapBoard.get("0");

                      for (int i = 0 ; i < boardList.size () ； i++){

                             BoardBean board = (BoardBean) boardList(i);

                             System.out.println(board.getBoardTitle() );

                             List sunBoardList1 = (List) mapBoard.get (board.getBoardId()+"");

                             for (int j= 0 ; j < 2 ; j++){

                                    BoardBean sunBoard = (BoardBean) sunBoardList1.get(j);

                                    System.out.println(sunBoard.getBoardTitle() );

 

                             }

                      }

               }

        }