用ABAP类实现队列

最新推荐文章于 2024-12-12 12:20:57 发布

cauwtj

最新推荐文章于 2024-12-12 12:20:57 发布

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分类专栏： ABAP 文章标签： returning constructor insert table methods report

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本文详细介绍了队列类的定义与实现过程，包括数据类型、方法构造、插入、删除操作及空队列判断等关键环节。通过实例解析，帮助读者掌握队列的基本原理与应用。

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REPORT ZPAB06_QUEUE.

CLASS QUEUE DEFINITION.
PUBLIC SECTION.
*Because the class is just for display.so the queue only can store
*integer.
    TYPES:BEGIN OF ST_QUEUE,
            ITEM TYPE I,
          END OF ST_QUEUE.
    DATA: NITEMS TYPE I READ-ONLY.                 "THE QUANTITY OF ITEM
    DATA: ITAB   TYPE TABLE OF ST_QUEUE,           "THE ITAB STORE ITEM
          WA     LIKE LINE OF ITAB.                "THE WA OF ITAB.
    METHODS:CONSTRUCTOR,                           "CONSTRUCTOR
            INSERT IMPORTING ITEM TYPE I,          "insert items
            REMOVE RETURNING VALUE(ITEM) TYPE I    "Remove the first ONE
                   EXCEPTIONS NOITEMS,             "NO ITEM IS QUEUE.
            PEEKFRONT RETURNING VALUE(ITEM) TYPE I "GET THE VALUE OF 1st
                      EXCEPTIONS NOITEMS,          "NO ITEM IS QUEUE.
*X='1' IF THE QUEUE IS EMPTY ELSE X = 0
            ISEMPTY   RETURNING VALUE(X) TYPE I.
ENDCLASS.
CLASS QUEUE IMPLEMENTATION.
METHOD CONSTRUCTOR.                              "CONSTRUCTOR
*initialize the queue
     NITEMS = 0.
     CLEAR ITAB.
ENDMETHOD.
METHOD INSERT.                                   "insert items
    CLEAR WA.                               "clear the work area
    WA-ITEM = ITEM.
    APPEND WA TO ITAB.                      "insert the items into queue
    NITEMS = NITEMS + 1.                           "ONE MORE ITEM
ENDMETHOD.
METHOD REMOVE.                                   "Remove the first one
    CLEAR WA.                               "clear the work area
    IF NITEMS <> 0.                   "Do while there are items in queue
      READ TABLE ITAB INTO WA INDEX 1."read the remove item into wa
      DELETE ITAB INDEX 1.            "REMOVE THE ITEM.
      ITEM = WA-ITEM.                 "Returning the value
      NITEMS = NITEMS - 1.            ""ONE LESS ITEM
    ELSE.
      RAISE NOITEMS.                  "there are no items.
    ENDIF.
ENDMETHOD.
METHOD PEEKFRONT.
    CLEAR WA.                         "clear the work area
    IF NITEMS <> 0.                   "Do while there are items in queue
      READ TABLE ITAB INTO WA INDEX 1."read the remove item into wa
      ITEM = WA-ITEM.                 "Returning the value
    ELSE.
      RAISE NOITEMS.                  "there are no items.
    ENDIF.
ENDMETHOD.
METHOD ISEMPTY.
     IF NITEMS = 0.                   "THE QUEUE IS EMPTY
       X = 1.
     ELSE.                            "THE QUEUE IS NOT EMPTY
       X = 0.
     ENDIF.
ENDMETHOD.
ENDCLASS.