Ramifications of extending subclass by creating abstract method in base
What r the ramification of extending subclass functionality by creating abstract method in base class?
javax.swing.JComponent is an example of an abstract
class with no abstract methods. That is why the
following works:
JComponent component = new JComponent(){};
Not to forget you cannot instantiate abstarct classes
public abstract class Test
public String getName()
return "Mike";
public static void main(String[] args)
Test tt = new Test();
System.out.println(tt.getName());
}and you would get the error
The type Test cannot be instantiated.
You remove the abstract keyword and it would compile
good.No I am not misinterpreting I know what he is saying but I am closing the door of misinterpretation which I felt was possible. ;)
cheers
Similar Messages
-
Getting error while creating abstract method
hi folks,
i facing issue for ABSTRACT Class.
I am trying to create abstarct method, (refered example from saptechnical site),
I created one attribute i-num, created one method AREA, in implementation area , i made it as Abstract, then i did syntax check, then it is giving below error.
*Class ZTEST_CLASS01_AB,Method AREA
The abstract method "AREA" can only be implemented after its
redefinition (METHODS AREA REDEFINITION).*
i tried all the ways..
created subclass for this, i writted some code in AREA of Sub-class, there it is giving dump, because first one is not activated properly..
could you please somebody help me on this.
SriHello Arshad,
Create a class(ZABSTRACT) and make its type as Abstract( Which means atleast one of its methods is abstract)
We can have abstract classes with all it's methods as non-abstract or concrete. A small example is given below:
CLASS gcl_abstract DEFINITION ABSTRACT.
PUBLIC SECTION.
METHODS concrete. "Concrete
ENDCLASS. "gcl_abstract DEFINITION
* CLASS gcl_abstract IMPLEMENTATION
CLASS gcl_abstract IMPLEMENTATION.
METHOD concrete.
WRITE: / `I'm a concrete method`.
ENDMETHOD. "concrete
ENDCLASS. "gcl_abstract IMPLEMENTATION
* CLASS gcl_abstract_sub DEFINITION
CLASS gcl_abstract_sub DEFINITION INHERITING FROM gcl_abstract.
PUBLIC SECTION.
METHODS concrete REDEFINITION.
ENDCLASS. "gcl_abstract_sub DEFINITION
* CLASS gcl_abstract_sub IMPLEMENTATION
CLASS gcl_abstract_sub IMPLEMENTATION.
METHOD concrete.
super->concrete( ).
WRITE: / 'Abstract class might not have abstract methods at all!'.
ENDMETHOD. "concrete
ENDCLASS. "gcl_abstract_sub IMPLEMENTATION
START-OF-SELECTION.
DATA: go_abstract TYPE REF TO gcl_abstract_sub.
CREATE OBJECT go_abstract.
go_abstract->concrete( ).
Although i will agree there is no point in making a class as abstract & having no abstract method
@Sri: Looks like you're trying to implement the abstract method "AREA" in the abstract class hence the error. For abstract method you cannot define their implementation in the corres. abstract class.
BR,
Suhas
Edited by: Suhas Saha on Mar 30, 2011 12:04 PM -
Implement abstract method from base class problem
Here is the example:
public abstract class AbstractClass{
protected double aVariable;
protected abstract double abstractMethod();
public class RealClass extends AbstractClass{
public double abstractMethod(){
return aVariable;
Error message:
RealClass should be declared abstract; it does not define abstractMethod() in AbstractClassI also compiled the code with Jdk1.3 and it
worked.. The code would not have compiled
if the access modifier in the derived class
was more restrictive(eg private )... -
Superclass and subclass and abstract method
Hi all,
I am a little bit confused about abstract methods.
I define a superclass without abstract keyword and an abstract method inside the superclass. Then I write a subclass to extend the superclass.
When I compile the source code I get error. It looks like I can't initiate an instance from the supercalss and/or subclass. If I put abstract key word in the superclass definition there is no problem at all. So my question: does abstract method needed to be defined in an abstract superclass only?
Thank for you input.Abstract methods can only be declared in an abstract class.
-
I'm a beginner in Java and just learn about abstract method and class.
However, i am wondering what is the point of using abstract method/class?
Because when I delete the abstract method and change the class name to public class XXXX( changed from "abstract class XXXX), my program still runs well, nothing goes different.
Is it because I haven't encountered any situation that abstract method is necessary or ?
Thanks!Yes - you probably haven't encountered a situation where you need an abstract.
Abstract classes are not designed to do anything on their own. They are designed to provide a template for other classes to extend by inheritance. What you have build sounds like a concrete class - one which you are creating instances of. Abstract classes are not designed to be ever instantiated in their pure form - they act like a partial building block, which you will complete in a class which extends the abstract.
An example might be a button class, which provides some core functionality (like rollover, rollout etc) but has an empty action method which has to be overwritten by a relevant subclass like 'StartButton'. In general, abstract classes may not be the right answer, and many people would argue that it is better to use an interface, which can be implemented instead of extended, meaning that you can ADD instead of REPLACING.
Not sure if that helps.. there are whole chapters in books on this kind of thing, so it's hard to explain in a couple of paragraphs. Do some google searches to find out more about how they work. -
Is not abstract and does not override abstract method actionPerformed
I dont how to corr. Please help!! and thank you very much!!
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class test extends JFrame implements ActionListener, ItemListener
private CenterPanel centerPanel;
private QuestionPanel questionPanel;
private ButtonPanel buttonPanel;
private ResponsePanel responsePanel;
private JButton b1,b2,b3,b4,b5; //Create five references to Jbutton instances
private JTextField t1,t2,t3,t4,t5; //Create five references to JTextField instances
private JLabel label1; //Create one references to JLabel instances
private JRadioButton q1,q2,q3; //Create three references to JRadioButton instances
private ButtonGroup radioGroup; //Create one references to Button Group instances
private int que1[] = new int[5]; //Create int[4] Array
private int que2[] = new int[5];
private int que3[] = new int[5];
private String temp1, temp2, temp3, temp4, temp5, temp6, temp7, temp8, temp9, temp10,
temp11, temp12, temp13, temp14, temp15;
public test (String header)
super(header);
Container container = getContentPane();
label1 = new JLabel ("PLease click on your response to ");
q1 = new JRadioButton("I understand most of the content of this subject",true);
add(q1);
q2 = new JRadioButton("I see the relevance of the subject to my degree",false);
add(q2);
q3 = new JRadioButton("The workload in this subject is appropriate",false);
add(q3);
radioGroup = new ButtonGroup(); //JRadioButton belong to ButtonGroup
radioGroup.add(q1);
radioGroup.add(q2);
radioGroup.add(q3);
JPanel buttonPanel = new JPanel();
JPanel responsePanel = new JPanel();
JPanel questionPanel = new JPanel();
JPanel centerPanel = new JPanel();
b1 = new JButton ("Strongly DISAGREE"); //Instantiate JButton with text
b1.addActionListener (this); //Register JButtons to receive events
b2 = new JButton ("DISAGREE");
b2.addActionListener (this);
b3 = new JButton ("Neither AGREE or DISAGREE");
b3.addActionListener (this);
b4 = new JButton ("AGREE");
b4.addActionListener (this);
b5 = new JButton ("Strongly AGREE");
b5.addActionListener (this);
buttonPanel.setLayout(new GridLayout(5,1));
buttonPanel.add(b1);
buttonPanel.add(b2);
buttonPanel.add(b3);
buttonPanel.add(b4);
buttonPanel.add(b5);
t1 = new JTextField ("0",3); //JTextField contains empty string
t2 = new JTextField ("0",3);
t3 = new JTextField ("0",3);
t4 = new JTextField ("0",3);
t5 = new JTextField ("0",3);
t1.setEditable( false );
t2.setEditable( false );
t3.setEditable( false );
t4.setEditable( false );
t5.setEditable( false );
responsePanel.setLayout(new GridLayout(5,1));
responsePanel.add(t1);
responsePanel.add(t2);
responsePanel.add(t3);
responsePanel.add(t4);
responsePanel.add(t5);
questionPanel.setLayout(new GridLayout(4,1));
questionPanel.add(label1);
questionPanel.add(q1);
questionPanel.add(q2);
questionPanel.add(q3);
centerPanel.add(buttonPanel,BorderLayout.CENTER);
centerPanel.add(responsePanel,BorderLayout.EAST);
container.add(centerPanel,BorderLayout.WEST);
container.add(questionPanel,BorderLayout.NORTH);
q1.addActionListener(
new ActionListener(){
public void actionPerformed( ActionEvent e )
{ //actionPerformed of all registered listeners
if (e.getSource() == b1) {
que1[0] = Integer.parseInt(t1.getText()) + 1;
String temp1 = String.valueOf(que1[0]);
t1.setText(temp1);
else if (e.getSource() == b2) {
que1[1] = Integer.parseInt(t2.getText()) + 1;
String temp2 = String.valueOf(que1[1]);
t2.setText(temp2);
else if (e.getSource() == b3) {
que1[2] = Integer.parseInt(t3.getText()) + 1;
String temp3 = String.valueOf(que1[2]);
t3.setText(temp3);
else if (e.getSource() == b4) {
que1[3] = Integer.parseInt(t4.getText()) + 1;
String temp4 = String.valueOf(que1[3]);
t4.setText(temp4);
else if (e.getSource() == b5) {
que1[4] = Integer.parseInt(t5.getText()) + 1;
String temp5 = String.valueOf(que1[4]);
t5.setText(temp5);
} //end action performed
q2.addActionListener(
new ActionListener(){
public void actionPerformed( ActionEvent e )
{ //actionPerformed of all registered listeners
if (e.getSource() == b1) {
que2[0] = Integer.parseInt(t1.getText()) + 1;
String temp6 = String.valueOf(que2[0]);
t1.setText(temp1);
else if (e.getSource() == b2) {
que2[1] = Integer.parseInt(t2.getText()) + 1;
String temp7 = String.valueOf(que2[1]);
t2.setText(temp7);
else if (e.getSource() == b3) {
que2[2] = Integer.parseInt(t3.getText()) + 1;
String temp8 = String.valueOf(que2[2]);
t3.setText(temp8);
else if (e.getSource() == b4) {
que2[3] = Integer.parseInt(t4.getText()) + 1;
String temp9 = String.valueOf(que2[3]);
t4.setText(temp9);
else if (e.getSource() == b5) {
que2[4] = Integer.parseInt(t5.getText()) + 1;
String temp10 = String.valueOf(que2[4]);
t5.setText(temp10);
} //end action performed
q3.addActionListener(
new ActionListener(){
public void actionPerformed( ActionEvent e )
{ //actionPerformed of all registered listeners
if (e.getSource() == b1) {
que3[0] = Integer.parseInt(t1.getText()) + 1;
String temp11 = String.valueOf(que3[0]);
t1.setText(temp11);
else if (e.getSource() == b2) {
que3[1] = Integer.parseInt(t2.getText()) + 1;
String temp12 = String.valueOf(que3[1]);
t2.setText(temp12);
else if (e.getSource() == b3) {
que3[2] = Integer.parseInt(t3.getText()) + 1;
String temp13 = String.valueOf(que3[2]);
t3.setText(temp13);
else if (e.getSource() == b4) {
que3[3] = Integer.parseInt(t4.getText()) + 1;
String temp14 = String.valueOf(que3[3]);
t4.setText(temp14);
else if (e.getSource() == b5) {
que3[4] = Integer.parseInt(t5.getText()) + 1;
String temp15 = String.valueOf(que3[4]);
t5.setText(temp15);
} //end action performed
}//end constructor test
public void itemStateChanged(ItemEvent item) {
//int state = item.getStateChange();
//if (q1 == item.SELECTED)
public class ButtonPanel extends JPanel
public ButtonPanel()
public class CenterPanel extends JPanel
public CenterPanel()
public class QuestionPanel extends JPanel
public QuestionPanel()
public class ResponsePanel extends JPanel
public ResponsePanel()
public static void main(String [] args)
test surveyFrame = new test("Student Survey") ;
surveyFrame.setSize( 500,300 );
surveyFrame.setVisible(true);
surveyFrame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
}//end main
}//end class testis not abstract and does not override abstract method actionPerformed
Oh, I see that the title of your post is an error message? Ok. Well, the test class is declared as implementing an ActionListener. That means the test class must have an actionPerformed() method. Your test class apparently does not.
It does not appear that the test class needs to implement ActionListener. You are using annonymous classes as listeners. -
Is not abstract and does not override abstract method tablechanged
I will remove all the gui code to make it shorter, but my problem lies with my InteractiveTableModelListener.
public class Meet extends JPanel{
private static void createAndShowGUI() {
JFrame frame = new JFrame("MEET_dataTable");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new Meet(), BorderLayout.CENTER);
frame.pack();
frame.setVisible(true);
public class InteractiveTableModelListener implements TableModelListener {
public void TableChanged(TableModelEvent evt) {
if (evt.getType() == TableModelEvent.UPDATE) {
int column = evt.getColumn();
int row = evt.getFirstRow();
dataTable.setColumnSelectionInterval(column + 1, column + 1);
dataTable.setRowSelectionInterval(row, row);
class InteractiveRenderer extends DefaultTableCellRenderer {
protected int interactiveColumn;
public InteractiveRenderer(int interactiveColumn) {
this.interactiveColumn = interactiveColumn;
public Component getTableCellRendererComponent(JTable dataTable,
Object value, boolean isSelected, boolean hasFocus, int row,
int column)
Component c = super.getTableCellRendererComponent(dataTable, value, isSelected, hasFocus, row, column);
if (column == interactiveColumn && hasFocus) {
if ((Meet.this.tableModel.getRowCount() - 1) == row &&
!Meet.this.tableModel.hasEmptyRow())
Meet.this.tableModel.addEmptyRow();
highlightLastRow(row);
return c;
public void highlightLastRow(int row) {
int lastrow = tableModel.getRowCount();
if (row == lastrow - 1) {
dataTable.setRowSelectionInterval(lastrow - 1, lastrow - 1);
else {
dataTable.setRowSelectionInterval(row + 1, row + 1);
dataTable.setColumnSelectionInterval(0, 0);
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
UIManager.put("swing.boldMetal", Boolean.FALSE);
createAndShowGUI();
}As i say, i have removed all the gui code to make it shorter, but in this code i create the table and add all the model to it. I am being returned with the error
Meet.InteractiveTableModelListener is not abstract and does not override abstract method tableChanged(javax.swing.event.TableModelEvent)in javax.swing.event.TableModelListener
what would be causing this error?
CheersSorry, just figured out my silly error, the method is tableChanged not TableChanged.
cheers
TOPIC CLOSED
Edited by: nick2price on Sep 11, 2008 7:08 AM -
Abstract method called in an abstract class
Hello,
I am writing some code that I'd like to be as generic as possible.
I created an abstract class called Chromozome. This abstract class has a protected abstract method called initialize().
I also created an abstract class called Algorithm which contains a protected ArrayList<Chromozome>.
I would like to create a non abstract method (called initializePopulation()) which would create instances of Chromozome, call their method initialize() and full the ArrayList with them.
In a practical matter, only subclass of Algorithm will be used, using an ArrayList of a subclass of Chromozome implementing their own version of initialize.
I have been thinking of that and concluded it was impossible to do. But I'd like to ask more talented peaple before forgetting it !
Thanks,
VincentOk, let's it is not impossible, juste that I had no idea of how doing it :-)
The difficulty is that Algorithm will never have to deal with Chromozome itself, but always with subclass of Chromozome. This is usually not an issue, but in that case, Algorithm is required to create instances of the desired subclass of Chromozome, but without knowing in advance wich subclass will be used (I hope what I say makes any sense).
Actually I may have found a way in the meantime, but maybe not the best one.
I created in Algorithm an abstract method :
protected abstract Chromozome createChromozome()The method initializePopulation will call createChromozome instead of calling directly the constructor and the initialize() method of Chromozome.
Then subclass of Algorithm will implement the method createChromozome using the desired subclass of Chromozome. -
Hi,
I want to use abstract methods in ABAP. I created an abstract class as base and another 'child' class that extends that class. Now, I want to have different implementations in different child classes. The problem is that the IDE redirects me to the base class when trying to to this. There is no possibility to set the method as abstract.
Do you know if that concept is implemented at all? Maybe I just forgot to configure something?!
What do you propose?
Thank you and best regards,
DanielHi,
If you are creating Local class using SE38, then just by writing "abstact" to the method it behaves like an abstract method.
If you are creating global class SE24, then genrally all interface methods are "abstract" methods so that we can ihberit and can redefine the methods for example: "IF_FLUSH_NOTIFY~BEFORE_FLUSH_NOTIFY" symbol ~ shows that it is an abstract method in the interface before to that.
So, even if it refer to its base class you can just implement them in the child classes by inheriting it.
Hope this helps you if yes try to assign some app. points.
Regards,
Suman -
"Abstract" method in a non-abstract class
Hi all.
I have a class "SuperClass" from which other class are extended...
I'd like to "force" some methods (method1(), method2, ...) to be implemented in the inherited classes.
I know I can accomplish this just implementing the superclass method body in order to throw an exception when it's directly called:
void method1(){
throw new UnsupportedOperationException();
}...but I was wondering if there's another (better) way...
It's like I would like to declare some abstract methods in a non-abstract class...
Any ideas?The superclass just models the information held by
the subclasses.
The information is taken from the database, by
accessing the proper table (one for each subclass).??
What do you mean by "models the information"?
You should use inheritance (of implementation) only when the class satisfies the following criteria:
1) "Is a special kind of," not "is a role played by a";
2) Never needs to transmute to be an object in some other class;
3) Extends rather than overrides or nullifies superclass;
4) Does not subclass what is merely a utility class (useful functionality you'd like to reuse); and
5) Within PD: expresses special kinds of roles, transactions, or things.
Why are you trying to force these mystery methodsfrom the superclass?
It's not mandatory for me to do it... I 'd see it
just like a further way to check that the subclasses
implements these methods, as they have to do.That's not a good idea. If the superclass has no relation to the database, it shouldn't contain methods (abstract or otherwise) related to database transactions.
The subclasses are the classes that handle db
transaction.
They are designed as a binding to a db table.And how is the superclass designed to handle db transactions? My guess (based on your description) is that it isn't. That should tell you right away that the subclasses should not extend your superclass. -
Non-abstract methods in a Abstract class
Abstract Class can contain Non-abstract methods.
and Abstract Classes are not instantiable as well
So,
What is the purpose of Non-abstract methods in a Abstract class.
since we can't create objects and use it
so these non-abstract methods are only available to subclasses.
(if the subclass is not marked as abstract)
is that the advantage that has.(availability in subclass)
??For example, the AbstractCollection class (in
java.util) provides an implementation for many of the
methods defined in the Collection interface.
Subclasses only have to implement a few more methods
to fulfill the Collection contract. Subclasses may
also choose to override the AbstractCollection
functionality if - for example - they know how to
provide an optimized implementation based on
characteristics of the actual subclass.Another example is the abstract class MouseAdapter that implements MouseListener, MouseWheelListener, MouseMotionListener, and that you can use instead of these interfaces when you want to react to one or two types of events only.
Quoting the javadocs: "If you implement the MouseListener, MouseMotionListener interface, you have to define all of the methods in it. This abstract class defines null methods for them all, so you can only have to define methods for events you care about." -
About abstract method read() in class InputStream (third message)
The subclass FilterInputStream is not abstract and extend InputStream: have you ever seen the implementation of that method in the source code available in SDK? It only calls that abstract method!!! I think it is not a very simple problem and anyway the answer is not in my diffrent books. Thanks for your non trivial answer.
Please post this as a "reply" in your original thread
http://forum.java.sun.com/thread.jspa?threadID=5192979&tstart=0
Don't start a new thread, simply reply to one of the other posts in the original thread (there is a button "reply" on the right hand side). -
Abstract method which when implemented will have different parameters
Hello to all,
I have an assignment but not looking for someone to do it for me. I am only searching for a suggestion on how to do the following.
Imagine having an application that needs to provide an estimate of the rent for different buildings.
Basically I start with by having a class name Building. This class has an abstract method called estimateRent.
I then create two classes that extend the class Building which are named Apartment and House. Both need to have the method estimateRent.
However the problem is that the rent for the Apartment is calculated on the nights passed in the flat and the people in it, while the rent for the House is just calculated on a month bases.
This means the estimateRent method requires to have different parameters depending if it is implemented inside the Apartment class or the House class.
Now I only know of two options.
The first option is to not declare the estimateRent method as an abstract method inside the Building class and just implemented inside the Apartment and House with different parameters. I do not like this option since in the future if a new Building comes in then I would like to impose the fact that that object needs to have a calculate method.
The second option is to make the estimateRent method as abstract inside the Building class however takes a parameter of either a String array or else a Map. Then the estimateRent within the Apartment class would search for the elements tagged as nights and people, and the House class would only search for the elements tagged as months!
However do not know if there are any other, better ways on how to do this. I am using Java 1.4 however if you only have answers for Java 5.0 then please post them again since I always like to learn something new :)
Thank You for any comments.
txThe implementation changes, yes.Yes that I could understand in the Strategy Pattern (in the document I read it was being compared with the Template Pattern).
Then you need to refactor your design.I tought about that, however if you read my first post you will notice that I have different criteria on which the costs need to be estimated. While the costs for a flat are estimated on the people staying in and nights slept there, the costs for the house are based only on the months stayed there regardless of the people living in. Now for me I feel that it is bad programming practice to create one method that can have all the parameters required for any scenario. I mean the following is NOT something I am going to do:
estimateCosts(int nights, int people, int months ... etc);
That's not a very elegant way of going about it.
What is the "Context" going to have?Yep I agree, but so far my limited brain has only come up with that! I am open to any other sugestion! always if i understand it first!
Basically the Context would better be named as Criteria and it would be an interface as follows:
interface Criteria{}
Then I would create two classes that implement the Criteria object as follows:
class AppartmentCriteria implements Criteria{
public Result estimateCosts(int nights, int people);
class HouseCriteria implements Criteria{
public Result estimateCosts(int months);
Now when I recieve the inputs, depending on the scenario the Criteria is typecasted and the correct parameters passed and we recieve the Result.
I feel the above sucks since I am not seeing it as an object oriented way of doing this out! Is there any other sugestions! The refactoring thing I am intrested in! however really I can not see how such a call to that method could be refectored!
Thank You,
tx.
PS: Sun has blocked my other account as well, and this time they did not even send me an email to confirm that I was registered successfuully :( Is there someone I can contact on this? I guess next time I will reply with tx53m :) -
Parent constructor calls abstract method
Hi everybody!
I'm wondering if there is something wrong with java or if the idea is just too ill?
Anyway, I think it would be great if this hierachy would work...
Two classes A and B.
Class A defines an astract method.
In A's constructor this abstract method is called.
Class B extends A and provides an implementation for the abstract method in A.
Class B also defines a member variable that is set in B's implementation of the abstract method.
In class' B constructor the parent constructor A() is called.
example:
public abstract class A {
public A() {
createComponents();
public abstract void createComponents();
public class B extends A {
private String string = null;
public B() {
super();
System.out.println("B::B() " + string);
public void createComponents() {
System.out.println("B::createComponents() begin");
string = new String("test");
System.out.println("B::createComponents() " + string);
public void describe() {
System.out.println("B::describe() " + string);
public static void main(String[] args) {
B b = new B();
b.describe();
}running the code above produces the following output:
B::createComponents() begin
B::createComponents() test
B::B() null
B::describe() null
why is the string member variable null in B's constructor??
thanks in advance
Peter Bachl
Polytechnic University of Upper Austria, Hagenberg
[email protected]The answer is that the call of the super-constructor
is allways done before the initialization
of the member variable. That's all and that's the
normal behavior.
order :
- initialization of static variables
- call to the super-constructor
- initialization of the instance variables
- execution of the constructor
Since this is the advanced forum it is relevant to point out that that is not exactly true.
There is a step in java that 'initializes' member variables before any constructors are called, super or other wise.
From the JLS 12.5...
Otherwise, all the instance variables in the new object, including those declared in superclasses, are initialized to their default values (4.5.5)
Using the following code as an example
class MyClass
int i1;
int i2 = 1;
.When creating an instance of the above there will be three 'initializations'
// Part of object creation...
i1 = 0; // The default value
i2 = 0; // The default value
// Part of construction...after super ctors called.
i2 = 1; // The variable initializer (see step 4 of JLS 12.5)
Unfortunately the descriptions are rather similar and so confusion can result as to when the assignment actually occurs. -
Abstract methods in ByteBuffer class
I'am a little confused with abstract methods get() and put() in ByteBuffer class.
Java API says:
public abstract class ByteBuffer
extends Buffer implements Comparable
// This is a partial API listing
public abstract byte get( );
public abstract byte get (int index);
public abstract ByteBuffer put (byte b);
public abstract ByteBuffer put (int index, byte b);
}Question is:
How can I call methods get() and/or put() when they are abstract - not implemented in ByteBuffer class?
ThanksYeah, it's a subclass of ByteBuffer. You can find out more about the class by using introspection.
But, you don't have to, to use this API. This is called "design-by-contract" (well, part of it anyway), and that's why the class is hidden with respect to the API docs. The idea is that an API is kind of like a contract, an agreement between the designer and the user of the API. The user of the API is given just what s/he needs to do the job. The designer might implement the API with more stuff that is immediately apparent, but the user doesn't need to know that stuff to use the API. This provides a good layer of abstraction around the API and makes code more flexible.
So, it's good to know how these things work -- that the ByteBuffer contract is serviced by hidden implementing classes -- but you don't have to know that to use ByteBuffer, and in fact you'd probably only make things difficult (buggy and hard to maintain) if you wrote code that used the fact that apparently the implementing subclass of ByteBuffer is HeapByteBuffer.
Maybe you are looking for
-
Wi-fi option on my ipod touch is greyed out?
Hi, My ipod touch won't connect via wi-fi and the option is greyed out when I try to connect manually. Two other ipod touches in my house are working fine. I've already reset it 3 times and no change. Help!
-
Is it possible for me to trade in my near-new iPhone 5 for a 5C?
I just signed-up for a iPhone 5 with Virgin Mobile Australia , just before the new iphones came out . Is it possible for me to trade it in to apple for a 5C and pay the difference? Many Thanks.
-
I clicked a link that says "Email" which is an option for me to select. It asks how I would like to contact someone, by email, phone, fax, etc. When I click "Email," a window pops up saying: "There is no email program associated to perform the reques
-
My iMac does not recognize or see an external drive.
Ref.: External USB M-DISC DVD+-RW CD RW Burner Writer Drive For Apple MacBook Air Pro iMac made by YunSen Tech. My iMac, Mac (27-inch, Late 2013), I bought in August 2014. Its SN is: C02MT0YWF8J4/OS X Yosemite. Version 10.10.1 Could you please help m
-
has anyone created any PLSQL using the XMLAGG and XMLELEMENT to create XML file output that can be read natively by MS Excel? I'd like to have/make something relatively simple that would have an API like this: make_me_excel( p_query => 'select a,b