What is the advantage of abstract class and method???

hi,
* Why a class is declared as abstract???
* What is the use of declaring a class as abstract???
* At what situation abstract class will be used???Thanks
JavaImran

To save you from the wrath of the Java experts on this forum, allow me as a relatively new Java user to advise you: do NOT post homework problems here; you're just going to get told to go google the answer. Which would be a good move on your part. Especially since I found the answer to your questions by googling them myself.

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  • ABSTRACT class and method

    Dear all Abaper experts,
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      PUBLIC SECTION.
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      PROTECTED SECTION.
        DATA speed TYPE i.
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    CLASS plane DEFINITION INHERITING FROM vehicle.
      PUBLIC SECTION.
        METHODS: rise.
      PROTECTED SECTION.
        DATA altitude TYPE i.
    ENDCLASS.
    CLASS ship DEFINITION INHERITING FROM vehicle.
    ENDCLASS.
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    CLASS vehicle IMPLEMENTATION.
      METHOD accelerate.
        speed = speed + 1.
      ENDMETHOD.
    ENDCLASS.
    CLASS plane IMPLEMENTATION.
      METHOD rise.
        altitude = altitude + 1.
      ENDMETHOD.
      METHOD write_status.
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        WRITE: / 'Altitude:', altitude.
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    ENDCLASS.
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          ship_ref  TYPE REF TO ship.
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    All answers are welcome and appreciate for the help.

    Hi,
    try this code I've rearranged your Class Implementation and just added the foll code;
      write_status REDEFINITION in the Definition part of the Subclass.
    * Class Declaration
    CLASS vehicle DEFINITION ABSTRACT.
      PUBLIC SECTION.
        METHODS: accelerate,
                 write_status ABSTRACT.
      PROTECTED SECTION.
        DATA speed TYPE i.
    ENDCLASS.
    * Class Implementation
    CLASS vehicle IMPLEMENTATION.
      METHOD accelerate.
        speed = speed + 1.
      ENDMETHOD.
    ENDCLASS.
    CLASS plane DEFINITION INHERITING FROM vehicle.
      PUBLIC SECTION.
        METHODS: rise,
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      PROTECTED SECTION.
        DATA altitude TYPE i.
    ENDCLASS.
    CLASS plane IMPLEMENTATION.
      METHOD rise.
        altitude = altitude + 1.
      ENDMETHOD.
      METHOD write_status.
        WRITE: / 'Plane speed:', speed.
        WRITE: / 'Altitude:', altitude.
      ENDMETHOD.
    ENDCLASS.
    CLASS ship DEFINITION INHERITING FROM vehicle.
      PUBLIC SECTION.
        METHODS: write_status redefinition. 
    ENDCLASS.
    CLASS ship IMPLEMENTATION.
      METHOD write_status.
        WRITE: / 'In Ship Class.'.
      ENDMETHOD.
    ENDCLASS.
    * Global Data
    DATA: plane_ref TYPE REF TO plane,
          ship_ref  TYPE REF TO ship.
    * Classical Processing Blocks
    START-OF-SELECTION.
      CREATE OBJECT: plane_ref,
                     ship_ref.
      CALL METHOD: plane_ref->accelerate,
                   plane_ref->rise,
                   plane_ref->write_status,
                   plane_ref->accelerate,
                   plane_ref->write_status,
                   ship_ref->write_status.
    Best Regards,
    Sunil.

  • Java abstract classes and methods

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  • Could you please send me the material Opps concepts Classes and Methods

    Hi Experts,
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    TABLES: zsflight.
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    G L O B A L I N T E R N A L T A B L E S
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    table must include fields for the traffic light and/or the color
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    Field for line color
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    TYPES: END OF st_sflight.
    TYPES: tt_sflight TYPE STANDARD TABLE OF st_sflight.
    DATA: gi_sflight TYPE tt_sflight.
    G L O B A L D A T A
    DATA: ok_code LIKE sy-ucomm,
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    DATA:
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    go_custom_container TYPE REF TO cl_gui_custom_container,
    o_event_receiver TYPE REF TO lcl_event_receiver.
    DATA:
    Work area for screen 200
    g_screen200 LIKE zsflight.
    Data for storing information about selected rows in the grid
    DATA:
    Internal table
    gi_index_rows TYPE lvc_t_row,
    Information about 1 row
    g_selected_row LIKE lvc_s_row.
    C L A S S E S
    CLASS lcl_event_receiver DEFINITION.
    PUBLIC SECTION.
    METHODS:
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    IMPORTING
    e_object e_interactive,
    handle_user_command FOR EVENT user_command OF cl_gui_alv_grid
    IMPORTING e_ucomm.
    ENDCLASS.
    CLASS lcl_event_receiver IMPLEMENTATION
    CLASS lcl_event_receiver IMPLEMENTATION.
    METHOD handle_toolbar.
    Event handler method for event toolbar.
    CONSTANTS:
    Constants for button type
    c_button_normal TYPE i VALUE 0,
    c_menu_and_default_button TYPE i VALUE 1,
    c_menu TYPE i VALUE 2,
    c_separator TYPE i VALUE 3,
    c_radio_button TYPE i VALUE 4,
    c_checkbox TYPE i VALUE 5,
    c_menu_entry TYPE i VALUE 6.
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    MOVE icon_change TO ls_toolbar-icon.
    MOVE 'Change flight' TO ls_toolbar-quickinfo.
    MOVE 'Change' TO ls_toolbar-text.
    MOVE ' ' TO ls_toolbar-disabled.
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    METHOD handle_user_command.
    Handle own functions defined in the toolbar
    CASE e_ucomm.
    WHEN 'CHANGE'.
    PERFORM change_flight.
    LEAVE TO SCREEN 0.
    ENDCASE.
    ENDMETHOD.
    ENDCLASS.
    S T A R T - O F - S E L E C T I O N.
    START-OF-SELECTION.
    SET SCREEN '100'.
    *& Module USER_COMMAND_0100 INPUT
    MODULE user_command_0100 INPUT.
    CASE ok_code.
    WHEN 'EXIT'.
    LEAVE TO SCREEN 0.
    ENDCASE.
    ENDMODULE. " USER_COMMAND_0100 INPUT
    *& Module STATUS_0100 OUTPUT
    MODULE status_0100 OUTPUT.
    DATA:
    For parameter IS_VARIANT that is sued to set up options for storing
    the grid layout as a variant in method set_table_for_first_display
    l_layout TYPE disvariant,
    Utillity field
    l_lines TYPE i.
    After returning from screen 200 the line that was selected before
    going to screen 200, should be selected again. The table gi_index_rows
    was the output table from the GET_SELECTED_ROWS method in form
    CHANGE_FLIGHT
    DESCRIBE TABLE gi_index_rows LINES l_lines.
    IF l_lines > 0.
    CALL METHOD go_grid->set_selected_rows
    EXPORTING
    it_index_rows = gi_index_rows.
    CALL METHOD cl_gui_cfw=>flush.
    REFRESH gi_index_rows.
    ENDIF.
    Read data and create objects
    IF go_custom_container IS INITIAL.
    Read data from datbase table
    PERFORM get_data.
    Create objects for container and ALV grid
    CREATE OBJECT go_custom_container
    EXPORTING container_name = 'ALV_CONTAINER'.
    CREATE OBJECT go_grid
    EXPORTING
    i_parent = go_custom_container.
    Create object for event_receiver class
    and set handlers
    CREATE OBJECT o_event_receiver.
    SET HANDLER o_event_receiver->handle_user_command FOR go_grid.
    SET HANDLER o_event_receiver->handle_toolbar FOR go_grid.
    Layout (Variant) for ALV grid
    l_layout-report = sy-repid. "Layout fo report
    Setup the grid layout using a variable of structure lvc_s_layo
    Set grid title
    gs_layout-grid_title = 'Flights'.
    Selection mode - Single row without buttons
    (This is the default mode
    gs_layout-sel_mode = 'B'.
    Name of the exception field (Traffic light field) and the color
    field + set the exception and color field of the table
    gs_layout-excp_fname = 'TRAFFIC_LIGHT'.
    gs_layout-info_fname = 'LINE_COLOR'.
    LOOP AT gi_sflight INTO g_wa_sflight.
    IF g_wa_sflight-paymentsum < 100000.
    Value of traffic light field
    g_wa_sflight-traffic_light = '1'.
    Value of color field:
    C = Color, 6=Color 1=Intesified on, 0: Inverse display off
    g_wa_sflight-line_color = 'C610'.
    ELSEIF g_wa_sflight-paymentsum => 100000 AND
    g_wa_sflight-paymentsum < 1000000.
    g_wa_sflight-traffic_light = '2'.
    ELSE.
    g_wa_sflight-traffic_light = '3'.
    ENDIF.
    MODIFY gi_sflight FROM g_wa_sflight.
    ENDLOOP.
    Grid setup for first display
    CALL METHOD go_grid->set_table_for_first_display
    EXPORTING i_structure_name = 'SFLIGHT'
    is_variant = l_layout
    i_save = 'A'
    is_layout = gs_layout
    CHANGING it_outtab = gi_sflight.
    *-- End of grid setup -
    Raise event toolbar to show the modified toolbar
    CALL METHOD go_grid->set_toolbar_interactive.
    Set focus to the grid. This is not necessary in this
    example as there is only one control on the screen
    CALL METHOD cl_gui_control=>set_focus EXPORTING control = go_grid.
    ENDIF.
    ENDMODULE. " STATUS_0100 OUTPUT
    *& Module USER_COMMAND_0200 INPUT
    MODULE user_command_0200 INPUT.
    CASE ok_code.
    WHEN 'EXIT200'.
    LEAVE TO SCREEN 100.
    WHEN'SAVE'.
    PERFORM save_changes.
    ENDCASE.
    ENDMODULE. " USER_COMMAND_0200 INPUT
    *& Form get_data
    FORM get_data.
    Read data from table SFLIGHT
    SELECT *
    FROM zsflight
    INTO TABLE gi_sflight.
    ENDFORM. " load_data_into_grid
    *& Form change_flight
    Reads the contents of the selected row in the grid, ans transfers
    the data to screen 200, where it can be changed and saved.
    FORM change_flight.
    DATA:l_lines TYPE i.
    REFRESH gi_index_rows.
    CLEAR g_selected_row.
    Read index of selected rows
    CALL METHOD go_grid->get_selected_rows
    IMPORTING
    et_index_rows = gi_index_rows.
    Check if any row are selected at all. If not
    table gi_index_rows will be empty
    DESCRIBE TABLE gi_index_rows LINES l_lines.
    IF l_lines = 0.
    CALL FUNCTION 'POPUP_TO_DISPLAY_TEXT'
    EXPORTING
    textline1 = 'You must choose a line'.
    EXIT.
    ENDIF.
    Read indexes of selected rows. In this example only one
    row can be selected as we are using gs_layout-sel_mode = 'B',
    so it is only ncessary to read the first entry in
    table gi_index_rows
    LOOP AT gi_index_rows INTO g_selected_row.
    IF sy-tabix = 1.
    READ TABLE gi_sflight INDEX g_selected_row-index INTO g_wa_sflight.
    ENDIF.
    ENDLOOP.
    Transfer data from the selected row to screenm 200 and show
    screen 200
    CLEAR g_screen200.
    MOVE-CORRESPONDING g_wa_sflight TO g_screen200.
    LEAVE TO SCREEN '200'.
    ENDFORM. " change_flight
    *& Form save_changes
    Changes made in screen 200 are written to the datbase table
    zsflight, and to the grid table gi_sflight, and the grid is
    updated with method refresh_table_display to display the changes
    FORM save_changes.
    DATA: l_traffic_light TYPE c.
    Update traffic light field
    Update database table
    MODIFY zsflight FROM g_screen200.
    Update grid table , traffic light field and color field.
    Note that it is necessary to use structure g_wa_sflight
    for the update, as the screen structure does not have a
    traffic light field
    MOVE-CORRESPONDING g_screen200 TO g_wa_sflight.
    IF g_wa_sflight-paymentsum < 100000.
    g_wa_sflight-traffic_light = '1'.
    C = Color, 6=Color 1=Intesified on, 0: Inverse display off
    g_wa_sflight-line_color = 'C610'.
    ELSEIF g_wa_sflight-paymentsum => 100000 AND
    g_wa_sflight-paymentsum < 1000000.
    g_wa_sflight-traffic_light = '2'.
    clear g_wa_sflight-line_color.
    ELSE.
    g_wa_sflight-traffic_light = '3'.
    clear g_wa_sflight-line_color.
    ENDIF.
    MODIFY gi_sflight INDEX g_selected_row-index FROM g_wa_sflight.
    Refresh grid
    CALL METHOD go_grid->refresh_table_display.
    CALL METHOD cl_gui_cfw=>flush.
    LEAVE TO SCREEN '100'.
    ENDFORM. " save_changes
    chk this blog
    /people/vijaybabu.dudla/blog/2006/07/21/topofpage-in-alv-using-clguialvgrid
    with regards,
    Hema.
    pls give points if helpful.

  • What is the benefit of abstract classes?

    I am little bit confuse regarding the benefits of the abstract classes. Can anybody helps me in this regard. I just want to know when and what situation we may decide that particular class needs an abstract method.
    Thanx

    I am little bit confuse regarding the benefits of the
    abstract classes. Can anybody helps me in this
    regard. I just want to know when and what situation
    we may decide that particular class needs an abstract
    method.Sorry if I sound weary of this question, but it is asked about 3-4 times a week. Rather than have us go through this tired exercise again, please search the forum for previous threads on this subject. You'll find about a gazillion. In fact, it's often a good idea to search the forum before asking a question as very often it has been asked and answered before.

  • What is the relation between main class and inner classes

    hi
    i want to make a UML design and o want to know how to draw the relation betwwen the main public class and inner classes?
    and what is the relation?

    BaffyOfDaffyA wrote:
    Please keep in mind that if you spell better you will get better answers and if you add duke stars you will get better answers and if you mark the thread as a question you will get better answers. That will make it look like you are paying attention and that you really want an answer.
    My best answer based on your rather vague question:
    A minimal public class in a file named "Minimal.java" in the directory named "minimal":
    package minimal;
    public class Minimal {
    private int variable;
    public Minimal(int var) {
    variable = var;
    public int getVariable() {
    return variable;
    }This would be an example of adding an inner class:
    package minimal;
    public class Minimal {
    private int variable;
    public Minimal(int var) {
    variable = var;
    public int getVariable() {
    return variable;
    public class Inner {
    private int innerVariable;
    public Inner(int var) {
    innerVariable = var;
    public int getInnerVariable() {
    return innerVariable;
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  • Abstract classes and methods with dollar.decimal not displaying correctly

    Hi, I'm working on a homework assignment and need a little help. I have two classes, 1 abstract class, 1 extends class and 1 program file. When I run the program file, it executes properly, but the stored values are not displaying correctly. I'm trying to get them to display in the dollar format, but it's leaving off the last 0. Can someone please offer some assistance. Here's what I did.
    File 1
    public abstract class Customer//Using the abstract class for the customer info
    private String name;//customer name
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    private int branchNumber;//The bank branch number
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        acctNo = acct;
        branchNumber = b;
    //toString method
    public String toString()
    String str;
        str = "Name: " + name + "\nAccount Number: " + acctNo + "\nBranch Number: " + branchNumber;
        return str;
    //Using the abstract method for the getCurrentBalance class
    public abstract double getCurrentBalance();
    }file 2
    public class AccountTrans extends Customer //
        private final double
        MONTHLY_DEPOSITS = 100,
        COMPANY_MATCH = 10,
        MONTHLY_INTEREST = 1;
        private double monthlyDeposit,
        coMatch,
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        //The constructor accepts as arguments the name, acctNo, and branchNumber
        public AccountTrans(String n, String acct, int b)
            super(n, acct, b);
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            monthlyDeposit = deposit;
        //The setCompanyMatch accepts the value for the monthly company match amount
        public void setCompanyMatch(double match)
            coMatch = match;
        //The setMonthlyInterest accepts the value for the monthly interest amount
        public void setMonthlyInterest(double interest)
            monthlyInt = interest;
        //toString method
        public String toString()
            String str;
            str = super.toString() +
            "\nAccount Type: Hybrid Retirement" +
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        //Using the getter method for the customer.java fields
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        public static void main(String[] args)
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            AccountTrans acctTrans = new AccountTrans("Jane Smith", "A123ZW", 435);
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            System.out.println(acctTrans);
            //This will display the current balance times 2 since the current
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    Get a hair cut!
    h1. The Ubiquitous Newbie Tips
    * DON'T SHOUT!!!
    * Homework dumps will be flamed mercilessly. [Feelin' lucky, punk? Well, do ya'?|http://www.youtube.com/watch?v=1-0BVT4cqGY]
    * Have a quick scan through the [Forum FAQ's|http://wikis.sun.com/display/SunForums/Forums.sun.com+FAQ].
    h5. Ask a good question
    * Don't forget to actually ask a question. No, The subject line doesn't count.
    * Don't even talk to me until you've:
        (a) [googled it|http://www.google.com.au/] and
        (b) had a squizzy at the [Java Cheat Sheet|http://mindprod.com/jgloss/jcheat.html] and
        (c) looked it up in [Sun's Java Tutorials|http://java.sun.com/docs/books/tutorial/] and
        (d) read the relevant section of the [API Docs|http://java.sun.com/javase/6/docs/api/index-files/index-1.html] and maybe even
        (e) referred to the JLS for "advanced" questions.
    * [Good questions|http://www.catb.org/~esr/faqs/smart-questions.html#intro] get better Answers. It's a fact. Trust me on this one.
        - Lots of regulars on these forums simply don't read badly written questions. It's just too frustrating.
          - FFS spare us the SMS and L33t speak! Pull your pants up, and get a hair cut!
        - Often you discover your own mistake whilst forming a "Good question".
        - Often you discover that you where trying to answer "[the wrong question|http://blog.aisleten.com/2008/11/20/youre-asking-the-wrong-question/]".
        - Many of the regulars on these forums will bend over backwards to help with a "Good question",
          especially to a nuggetty problem, because they're interested in the answer.
    * Improve your chances of getting laid tonight by writing an SSCCE
        - For you normal people, That's a: Short Self-Contained Compilable (Correct) Example.
        - Short is sweet: No-one wants to wade through 5000 lines to find your syntax errors!
        - Often you discover your own mistake whilst writing an SSCCE.
        - Often you solve your own problem whilst preparing the SSCCE.
        - Solving your own problem yields a sense of accomplishment, which makes you smarter ;-)
    h5. Formatting Matters
    * Post your code between a pair of &#123;code} tags
        - That is: &#123;code} ... your code goes here ... &#123;code}
        - This makes your code easier to read by preserving whitespace and highlighting java syntax.
        - Copy&paste your source code directly from your editor. The forum editor basically sucks.
        - The forums tabwidth is 8, as per [the java coding conventions|http://java.sun.com/docs/codeconv/].
          - Indents will go jagged if your tabwidth!=8 and you've mixed tabs and spaces.
          - Indentation is essential to following program code.
          - Long lines (say > 132 chars) should be wrapped.
    * Post your error messages between a pair of &#123;code} tags:
        - That is: &#123;code} ... errors here ... &#123;code}
        - OR: &#91;pre]&#123;noformat} ... errors here ... &#123;noformat}&#91;/pre]
        - To make it easier for us to find, Mark the erroneous line(s) in your source-code. For example:
            System.out.println("Your momma!); // <<<< ERROR 1
        - Note that error messages are rendered basically useless if the code has been
          modified AT ALL since the error message was produced.
        - Here's [How to read a stacktrace|http://www.0xcafefeed.com/2004/06/of-thread-dumps-and-stack-traces/].
    * The forum editor has a "Preview" pane. Use it.
        - If you're new around here you'll probably find the "Rich Text" view is easier to use.
        - WARNING: Swapping from "Plain Text" view to "Rich Text" scrambles the markup!
        - To see how a posted "special effect" is done, click reply then click the quote button.
    If you (the newbie) have covered these bases *you deserve, and can therefore expect, GOOD answers!*
    h1. The pledge!
    We the New To Java regulars do hereby pledge to refrain from flaming anybody, no matter how gumbyish the question, if the OP has demonstrably tried to cover these bases. The rest are fair game.

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