Use method of parent instance ...

It is possible to use method of parent instance?
For example:
Instance A of class B create instance C of class D.
I want to use method of instance A from method of instance C.
Class B and D have no relation.
Passing reference to instance A as parameter is not useable.
Thanks for any idea.
Marcel

Hello,
If you have no link between A and C, you must use references.
You can use this:
class B
   public D createC()
      return new D(this)
   public void something()
class D
   B Aref = null;
   public D(B newARef)
      Aref = newARef;
   public void aMethod()
      something()
      ARef.something();
   public void something()
}

Similar Messages

Not able to access parent instance variable in outside of methods in child

Hi,
I am not getting why i am not able to access parent class instance variable outside the child class intance methods.
class Parent
     int a;
class Child extends Parent
     a = 1; // Here i am getting a compilation error that Syntax error on token "a", VariableDeclaratorId expected after this token
     void someMethod()
          a = 1; // Here i am not getting any compilation error while accessing parent class variable
}Can any one please let me know exact reason for this and what is the error talks about?
Thanks,
Uday
Edited by: Udaya Shankara Gandhi on Jun 13, 2012 3:30 AM

You can only put assignments or expressions inside methods, constructors or class initializors, or when declaring a variable.
It has nothing to the with Child extending Parent.
class Parent {
    int a = 1;
    { a = 1; }
    public Parent() {
        a = 1;
   public void method() {
       a = 1;
}

ALV Grid Using Methods-handle_top_of_page

riends please explain how to resolve the below issue.
I am working on ALV Grid using methods & trying to display
page heading using handle_top_of_page event.
I have defined & implemented the above method and in the implementation I have
given a write statement, which has to be displayed on the top of page.
I have also set the handler for top of page.
The program does not have any errors, but top of page event is not triggered, what might be the problem.
Regards,
Usha

Hi,
Check this code
Class definition :
      CLASS v_lcl_event_receiver DEFINITION
CLASS v_lcl_event_receiver DEFINITION.
PUBLIC SECTION.
    METHODS:
    handle_print_top_of_page FOR EVENT print_top_of_page OF
                                       cl_gui_alv_grid,
    handle_top_of_page FOR EVENT top_of_page OF
                                 cl_gui_alv_grid.
ENDCLASS.
      CLASS V_LCL_EVENT_RECEIVER IMPLEMENTATION
CLASS v_lcl_event_receiver IMPLEMENTATION.
METHOD handle_print_top_of_page.
    IF sy-pagno = 1.
        PERFORM top_of_page.
    ENDIF.
ENDMETHOD.
METHOD handle_top_of_page.
      PERFORM top_of_page.
ENDMETHOD.
ENDCLASS.
DATA:        v_event_receiver      TYPE REF TO v_lcl_event_receiver.
FORM top_of_page.
WRITE: text-020,
ENDFORM.                    " top_of_page
In PBo of the screen
   DATA: v_split            TYPE REF TO cl_gui_easy_splitter_container,
         v_contnr_top       TYPE REF TO cl_gui_container,
         v_contnr_bot       TYPE REF TO cl_gui_container,
         v_grid_02          TYPE REF TO cl_gui_alv_grid,
         v_html             TYPE REF TO cl_dd_document,
         v_text20(255)      TYPE c,
         v_text16(255)      TYPE c,
FORM f9000_objects_create.
IF cl_gui_alv_grid=>offline( ) IS INITIAL.
Create a container
    CREATE OBJECT o_dockingcontainer
      EXPORTING
        ratio                       = '95'
      EXCEPTIONS
        cntl_error                  = 1
        cntl_system_error           = 2
        create_error                = 3
        lifetime_error              = 4
        lifetime_dynpro_dynpro_link = 5
        others                      = 6.
    IF sy-subrc NE 0.
      MESSAGE i000 WITH text-e01."Error in creating Docking container
      LEAVE LIST-PROCESSING.
    ENDIF.
    CREATE OBJECT v_split
         EXPORTING
           parent            = o_dockingcontainer
         ORIENTATION       = 0
           sash_position     = 25
           with_border       = 0
         EXCEPTIONS
           cntl_error        = 1
           cntl_system_error = 2
           others            = 3.
    IF sy-subrc NE 0.
      MESSAGE i000 WITH text-e01."Error in creating Docking container
      LEAVE LIST-PROCESSING.
    ENDIF.
Get the containers of the splitter control
    v_contnr_top = v_split->top_left_container.
    v_contnr_bot = v_split->bottom_right_container.
    CREATE OBJECT o_alvgrid
   EXPORTING
     i_parent = o_dockingcontainer.
Create an instance of alv control
    CREATE OBJECT o_alvgrid
         EXPORTING i_parent = v_contnr_bot.
Object for display of selection parameters in HTML top container
    CREATE OBJECT v_html
         EXPORTING
           style = 'ALV_GRID'.
Must be after the SET HANDLER for TOP_OF_PAGE and foreground only
    CALL METHOD o_alvgrid->list_processing_events
                     EXPORTING i_event_name = 'TOP_OF_PAGE'
                               i_dyndoc_id = v_html.
    v_text20 = text-020(summary Record counts)Any text.
    CALL METHOD v_html->add_gap
                EXPORTING
                  width         = 120.
    CALL METHOD v_html->add_text
           EXPORTING
             text          = v_text20.
    CALL METHOD v_html->new_line.
Display Text-016
    v_text16 = text-016.
    CALL METHOD v_html->add_gap
                EXPORTING
                  width         = 1.
    CALL METHOD v_html->add_text
           EXPORTING
             text          = v_text16.
    v_text16 = v_sap_recon.
    CALL METHOD v_html->add_gap
                EXPORTING
                  width         = 1.
    CALL METHOD v_html->add_text
           EXPORTING
             text          = v_text16.
    CALL METHOD v_html->new_line.
Display the data
    CALL METHOD v_html->display_document
      EXPORTING
         parent             = v_contnr_top.
Handle the event
    CALL METHOD o_alvgrid->list_processing_events
                        EXPORTING i_event_name = 'PRINT_TOP_OF_PAGE'.
IN PBO while populating in the output table
FORM f9004_display_data TABLES   p_report_tab
                                 p_fieldcat.
CALL METHOD o_alvgrid->set_table_for_first_display
    EXPORTING
       is_variant                    = w_variant
       i_save                        = c_a
       is_layout                     = w_layout
    CHANGING
       it_outtab                     = p_report_tab[]
       it_fieldcatalog               = p_fieldcat[]
    EXCEPTIONS
       invalid_parameter_combination = 1
       program_error                 = 2
       too_many_lines                = 3
       OTHERS                        = 4.
IF sy-subrc <> 0.
    MESSAGE i000 WITH text-e06."Error in ALV report display
    LEAVE LIST-PROCESSING.
ENDIF.
Create object
IF v_event_receiver IS INITIAL.
    CREATE OBJECT v_event_receiver.
ENDIF.
SET HANDLER v_event_receiver->handle_print_top_of_page FOR o_alvgrid.
SET HANDLER v_event_receiver->handle_top_of_page FOR o_alvgrid.
Hope this helps.

SQL Server Express Performance Limitations With OGC Methods on Geometry Instances

I will front load my question. Specifically, I am wondering if any of the feature restrictions with SQL Server Express cause performance limitations/reductions with OGC methods on geometry instances, e.g., STIntersects? I have spent time reading
various documents about the different editions of SQL Server, including the Features Supported by the Editions of SQL Server 2014, but nothing is jumping out at me. The
limited information on spatial features in the aforementioned document implies spatial is the same across all editions. I am hoping this is wrong.
The situation.... I have roughly 200,000 tax parcels within 175 taxing districts. As part of a consistency check between what is stored in tax records for taxing district and what is identified spatially, I set up a basic point-in-polygon query
to identify the taxing district spatially and then count the number of parcels within in taxing district. Surprisingly, the query took 66 minutes to run. As I pointed out, this is being run on a test machine with SQL Server Express.
Some specifics.... I wrote the query a few different ways and compared the execution plans, and the optimizer always choose the same plan, which is good I guess since it means it is doing its job. The execution plans show a 'Clustered Index Seek
(Spatial)' being used and only costing 1%. Coming in at 75% cost is a Filter, which appears to be connected to the STIntersects predicate. I brute forced alternate execution plans using HINTS, but they only turned out worse, which I guess is also
good since it means the optimizer did choose a good plan. I experimented some with changing the spatial index parameters, but the impact of the options I tried was never that much. I ended up going with "Geometry Auto Grid" with 16 cells
per object.
So, why do I think 66 minutes is excessive? The reason is that I loaded the same data sets into PostgreSQL/PostGIS, used a default spatial index, and the same query ran in 5 minutes. Same machine, same data, SQL Server Express is 13x slower than
PostgreSQL. That is why I think 66 minutes is excessive.
Our organization is mostly an Oracle and SQL Server shop. Since more of my background and experience are with MS databases, I prefer to work with SQL Server. I really do want to understand what is happening here. Is there something I can
do different to get more performance out of SQL Server? Does spatial run slower on Express versus Standard or Enterprise? Given I did so little tuning in PostgreSQL, I still can't understand the results I am seeing.
I may or may not be able to strip the data down enough to be able to send it to someone.

Tessalating the polygons (tax districts) is the answer!
Since my use of SQL Server Express was brought up as possibly contributing to the slow runtime, the first thing I did was download an evaluation version of Enterprise Edition. The runtime on Enterprise Edition dropped from 66 minutes to 57.5 minutes.
A reduction of 13% isn't anything to scoff at, but total runtime was still 11x longer than in PostgreSQL. Although Enterprise Edition had 4 cores available to it, it never really spun up more than 1 when executing the query, so it doesn't seem
to have been parallelizing the query much, if at all.
You asked about polygon complexity. Overall, a majority are fairly simple but there are some complex ones with one really complex polygon. Using the complexity index discussed in the reference thread, the tax districts had an average complexity
of 4.6 and a median of 2.7. One polygon had a complexity index of 120, which was skewing the average, as well as increasing the runtime I suspect. Below is a complexity index breakdown:
Index
NUM_TAX_DIST
1
6
<2
49
<3
44
<4
23
<5
11
<6
9
<7
9
<8
4
<9
1
<10
4
>=10
14
Before trying tessellation, I tweaked the spatial indexes in several different ways, but the runtimes never changed by more than a minute or two. I reset the spatial indexes to "geometry auto grid @ 32" and tried out your tessellation functions
using the default of 5000 vertices. Total runtime 2.3 minutes, a 96% reduction and twice as fast as PostgresSQL! Now that is more what I was expecting before i started.
I tried using different thresholds, 3,000 and 10,000 vertices but the runtimes were slightly slower, 3.5 and 3.3 minutes respectively. A threshold of 5000 definitely seems to be a sweet spot for the dataset I am using. As the thread you referenced
discussed, SQL Server spatial functions like STIntersect appear to be sensitive to the number of vertices of polygons.
After reading your comment, it reminded me of some discussions with Esri staff about ArcGIS doing the same thing in certain circumstances, but I didn't go as far as thinking to apply it here. So, thanks for the suggestion and code from another post.
Once I realized the SRID was hard coded to 0 in tvf_QuarterPolygon, I was able to update the code to set it to the same as the input shape, and then everything came together nicely.

Problem in using methods in Interface, CharacterData in org.w3c.dom

Hi,
I am trying to use two methods provided by CharacterData Interface. The getData() and getLength() methods. It is giving error when I use it like this
String dat3 = myNode.getData();
Is there anything wrong in the way I am using it? Can somebody please help me with this?
Please find below the code I am using.
One more question - I have the below statement in my code which is giving an error when there is no data in the XML node.
String dat = myNode.getFirstChild().getNodeValue();
Is there any way to bypass this?
Thankyou
NodeList myNodeList=myElement.getElementsByTagName("EVENT-EXPIRY-DATE");
for (int i = myNodeList.getLength(); i>0;i--)
Node myNode = myNodeList.item(i-1);
boolean delflag = false;
String dat3 = myNode.getData();
int len = myNode.getLength();
}

CharacterData, which is an extension of Node, is the interface that define the getData resposability. In your code you try to use that method in an instance of type Node which doesn't have it.

Using methods from another Form C#

Hello!
I'm having some trouble using methods from one Form in another one. Here's the deal:
This is a snippet from my 'main' form:
public partial class PRINCIPAL : Form
//some variables here
Form2 Config = new Form2();
Form3 Cadastro = new Form3();
public PRINCIPAL()
InitializeComponent();
//code goes on and on
//Here's the method I want to call on the other forms (Form2 and Form3)
public void salva_banco()
this.Validate();
this.projetoBindingSource.EndEdit();
this.modulosBindingSource.EndEdit();
this.funcaoBindingSource.EndEdit();
this.estadosBindingSource.EndEdit();
this.tableAdapterManager.UpdateAll(this.database1DataSet);
//And here is where I show Form3
private void projetoDataGridView_CellDoubleClick_1(object sender, DataGridViewCellEventArgs e)
Cadastro.ShowDialog();
//And here is where I show Form2
private void funcaoDataGridView1_CellDoubleClick(object sender, DataGridViewCellEventArgs e)
Config.ShowDialog();
}// And the code keeps on going}
And this is a snippet from Form3:
public partial class Form3 : Form
public Form3()
InitializeComponent();
private void Form3_Load(object sender, EventArgs e)
this.projetoTableAdapter.Fill(this.database1DataSet.Projeto);
this.modulosTableAdapter.Fill(this.database1DataSet.Modulos);
private void btnOK_Click(object sender, EventArgs e)
if (projetoTextBox.Text == "")
MessageBox.Show("some text here");
else
////// HERE IS THE PLACE WHERE I WANT TO CALL THE METHOD! "salva_banco()"
I've read lots of suggestions but none satisfied my condition.
I appreciate any help.
Thanks.

You need to find the instance of the PRINCIPAL form to call the method on. If you know there will always be exactly one open you can use:
var principalForm = Application.OpenForms.OfType<PRINCIPAL>().Single();
principalForm.salva_banco();
David
David http://blogs.msdn.com/b/dbrowne/

How can I apply a timestretch to different null objects and then use them to parent layers?

I am using several hundred stills which are held on screen for different lengths of time. Is there a way to create null objects with various timestretch values and then use them to parent my stills?
I'm trying to find an equivalent to the 'paste attributes' function in Final Cut Pro.
Thanks in advance
A

If you have movement on the stills you can set up expressions based on in and out points. That's what I do. I then drop all my stills in order into a comp then set the out point for all stills for the longest duration. I then set group colors for layers that I want to make different lengths, do a group select and then adjust the out points for those layers. When I'm done I sequence the layers using the keyframe assistant.
The other way I work is to use an audio track with markers for timing. I have an expression that reads the markers and sets opacity for the layers based on pairs of markers. The motion is also controlled by expressions. That's an even faster way to set up an animated slide show.
The last way I work is just to set in an out points for all layers, sequence the layers, use expressions to do the motion and then use time remapping on a pre-comp to adjust the timing of the slide show. All methods are quick and easy.
Here's a fly in bounce and then drop out fxx preset that will give you an idea of how expressions based on in and out point work for slide shows. You just drag the layer to it's resting position, apply the animatiokn preset and the layer flys in, bounces, and then drops out the bottom of the comp. Works in 2D and 3D space.

Last use of RMI object instance

I have an RMI object with instance variables. As clients of this
remote object method make calls on it, these instance variables
are used and modified. My question is; Is there a way where I can
check when the last call from the client where made using a certain
instance?
Do I have to have separate timer methods for each instance to track
the time elapsed since last use?
Any answers are appreciated.
/Mats

Perhaps you could post something describing what you are trying to do. (Sounds like you want to keep track of last-used-time on a bunch of data elements?)

Static Classes/Methods vs Objects/Instance Classes/Methods?

Hi,
I am reading "Official ABAP Programming Guidelines" book. And I saw the rule:
Rule 5.3: Do Not Use Static Classes
Preferably use objects instead of static classes. If you don't want to have a multiple instantiation, you can use singletons.
I needed to create a global class and some methods under that. And there is no any object-oriented design idea exists. Instead of creating a function group/modules, I have decided to create a global class (even is a abstract class) and some static methods.So I directly use these static methods by using zcl_class=>method().
But the rule above says "Don't use static classes/methods, always use instance methods if even there is no object-oriented design".
The book listed several reasons, one for example
1-) Static classes are implicitly loaded first time they are used, and the corresponding static constructor -of available- is executed. They remain in the memory as long as the current internal session exists. Therefore, if you use static classes, you cannot actually control the time of initialization and have no option to release the memory.
So if I use a static class/method in a subroutine, it will be loaded into memory and it will stay in the memory till I close the program.
But if I use instance class/method, I can CREATE OBJECT lo_object TYPE REF TO zcl_class then use method lo_object->method(), then I can FREE lo_object to delete from the memory. Is my understanding correct?
Any idea? What do you prefer Static Class OR Object/Instance Class?
Thanks in advance.
Tuncay

@Naimesh Patel
So you recommend to use instance class/methods even though method logic is just self-executable. Right?
<h3>Example:</h3>
<h4>Instance option</h4>
CLASS zcl_class DEFINITION.
METHODS add_1 IMPORTING i_input type i EXPORTING e_output type i.
METHODS subtract_1 IMPORTING i_input type i EXPORTING e_output type i.
ENDCLASS
CLASS zcl_class IMPLEMENTATION.
METHOD add_1.
    e_output = i_input + 1.
ENDMETHOD.
METHOD subtract_1.
    e_output = i_input - 1.
ENDMETHOD.
ENDCLASS
CREATE OBJECT lo_object.
lo_object->add_1(
exporting i_input = 1
importing e_output = lv_output ).
lo_object->subtract_1(
exporting i_input = 2
importing e_output = lv_output2 ).
<h4>Static option</h4>
CLASS zcl_class DEFINITION.
CLASS-METHODS add_1 IMPORTING i_input type i EXPORTING e_output type i.
CLASS-METHODS subtract_1 IMPORTING i_input type i EXPORTING e_output type i.
ENDCLASS
CLASS zcl_class IMPLEMENTATION.
METHOD add_1.
    e_output = i_input + 1.
ENDMETHOD.
METHOD subtract_1.
    e_output = i_input - 1.
ENDMETHOD.
ENDCLASS
CREATE OBJECT lo_object.
lo_object->add_1(
zcl_class=>add_1(
exporting i_input = 1
importing e_output = lv_output ).
lo_object->subtract_1(
zcl_class=>subtract_1(
exporting i_input = 2
importing e_output = lv_output2 ).
So which option is best? Pros and Cons?

Parent Instance creating many child instances in SOA-INFRA

Hi,
We have deleted a parent instance from SOA-INFRA database.Even after deletion it keeps on creating child instances. How to identify all the child instances of the parent instance in SOA-INFRA schema . Also, we searched a lot but were unable to get much details about SOA_INFRA schema.
Please suggest and tell us the reasoning behind why many child instances getting created? Any suggestions will help us.
Thanks in advance.

It just provides the table names but doesnt provide information like which table is referred which table. Also, can anyone let me know how the instance id(when a request is submitted) is created in SOA-INFRA schema and how it is used other tables because we still see the child instances is getting created from the parent instance.
Any help will be appreciated.
Thanks.

Executing Child Taskflow Method from parent taskflow page

Hi All,
I have one issue with checking dirty data form Parent Taskflow button to check dirty data update in Child Taskflow page's view Object.
JDev version: 11.1.1.3
Scenario :
Outer Container page has back button which need to check wherethere child taskflow has dirty data update or not. Child Taskflow transaction is always create new transaction and non-shared. But from ControllerContext, the root am service still associated with other viewobjects i.e. is loaded in others tabs in that outer container page, which is also checking dirty data from another tabs' viewobject dirty data checking (I need to avoid this issue that's why not working for me with controller context). I am thining to execute the child taskflow method from parent page on back button to check dirty data update for that tabs' page only. For it, how can we get access child taskflow method from parent page with static region taskflow. Is there any solution to implement like this? thank you so much.
- Robin

Hi,
this should work:
1. child task flow has input parameter "parentBean" defined.
2. The child task flow has a managed bean "ChildBean" defined in pageFlowScope with a property "parentBean" with setter/getter.
3. the parentBean input parameter references (in its value roperty) #{pageFlowScope.childBean.parentBean}
4. The parent bean is configured on the parent view task flow (viewScope) and passed as a task flow binding input parameter. The parent bean has a boolean property "childFlowTransactionDirty"
This allows the child bean to invoke the parent bean childFlowTransactionDirty to tell it that the transaction is dirty. On the parent view, you would just check the parentBean state for this property.
Next is how you set the value on the parentBean from the childTaskFlow. One option is to use a RegionController on the PageDef file of ADF bound views in the child task flow.
public class MyRegionController implements RegionController {
    public MyRegionController(){
    public boolean refreshRegion(RegionContext regionContext) {
     int refreshFlag = regionContext.getRefreshFlag();
      //get access to the ChildBean and its parentBean property. Then call
      //ControllerContext .... to check the transaction state
      //update the childFlowTransactionDirty property
      ((DCBindingContainer)regionContext.getRegionBinding()).refresh(refreshFlag);
      return true;
    @Override
    public boolean validateRegion(RegionContext regionContext) {
        regionContext.getRegionBinding().validate();
        return false;
    public boolean isRegionViewable(RegionContext regionContext) {
        return regionContext.getRegionBinding().isViewable();
    @Override
    public String getName() {
        return this.getClass().toString();
}Next: When users press the back button in the parent view, you call the ParentView bean childFlowTransactionDirty to check the child task flow transaction to be dirty or not
Frank

What is the advantage of using methods to return objects?

Hello there,
What is the advantage of using static methods to return
objects? Isnt this a Factory Pattern ?
What is the real advantage of using methods to return objects
rather than using public constructors to create objects ?
Can some one please explain
Regards

I think there were two questions. The first (why
static) is well answered but I hope somebody can
answer the general question - why whatever =
createSomething(); as opposed to whatever
= new Something(); - because inquiring minds
want to know.I thought I answered that question. Perhaps I need to be more specific.
For the Singleton pattern, you don't want a new instance (except possibly the first time, if you're using lazy instantiation).
For the Factory pattern, you might not always want an instance of the actual class containing the static methods, so new won't work.
If, on the other hand, neither of the above holds, there is no reason not to use new (unless, of course, anyone can come up with another use of static creators).
RObin

Use methods of another class

Dear Sir/madam,
i have a question about using methods of another class. I will explane:
i have made a class which is called A. This class has some attributes (studentName and examRank) and some methods.
Now i need to made another class called B. Now i want to make an array where i can add some attributes of objects which i made of class A. How can i do that?
Kind regards

Here's a for-instance that doesn't use your exact program but demonstrates the point:
public class A
int value;
String name;
public A(int value, String name)
    this.name = name;
    this.value = value;
public int getValue()
    return value;
public String getName()
    return name;
public String toString()
    return name + ": " + value;
import java.util.Arrays;
import java.util.Random;
public class B
private static final String[] NAMES =
    "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
private static final int MAX = 100;
private A[] myAs = new A[NAMES.length];
private Random random = new Random();
public B()
    for (int i = 0; i < myAs.length; i++)
      myAs[i] = new A(random.nextInt(MAX), NAMES);
public String toString()
return Arrays.toString(myAs);
public int getTotal()
int temp = 0;
for (int i = 0; i < myAs.length; i++)
temp += myAs[i].getValue();
return temp;
public static void main(String[] args)
B b = new B();
System.out.println(b);
System.out.println("Total: " + b.getTotal());

Class methods vs. Instance methods

When shall we use class methods instead of instance methods , and vice versa?
By going through the Java Tutorial, it only says the following.
A common use for static methods is to access static fields....
I am definitely sure that class methods aren't just exist for accessing static fields of a class.
PS. I understand that instance methods belong to the object that is instantiated and class methods belong to the class itself.

Jay-K wrote:
JoachimSauer wrote:
P.S.: I wouldn't call them "class methods". They are called static methods in Java. It helps to stay with the common, widely-used terminology.Thanks, its good to know what the norms are.
but i wonder why the Java Tutorial states it clearly "Class Methods" over here [http://java.sun.com/docs/books/tutorial/java/javaOO/classvars.html|http://java.sun.com/docs/books/tutorial/java/javaOO/classvars.html]
Because strictly speaking that's what they are. They belong to classes, rather than instances of classes. The world-at-large, though, has found that term to be a bit ambiguous, especially when discussing fields - it's not uncommon to see instance variables referred to as "class variables" by newbies - so it's kind-of self-corrected.

Use methods in other classes

Can I use methods from other classes than the class that myClass extends?
ex. myClass extends parentClass{
myMethod()
myMethod() is declared in i third class. Is this possible or can I only use classes from the parent class?
-Thanks-

I'm not really sure what the previous two answers were getting at.
Yes, you can use methods all the way up the class hierarchy, as long as they are visible.
For example, Object implements toString(). You can call toString() on any object in Java and it will render the object to a string in one way or another. That is because toString() is public.
If toString() were protected, you would only be able to call the method if you were a subclass of of that object (or in the same package), which would make the toString() method much less useful.
I would suggest reading up on the differences in the four visibility modifiers (private, (default), protected, and public). Private is the only one which nothing else can call. If you are public or protected, any subclass can call the method, even if there are 20 superclasses between the implementor and the caller.
Good luck!
Steve

Use method of parent instance ...

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