Call a method of a class in a constructor of another class?

Is this good programming or should i do it in another way?
Consider an ordering system, where I have three classes, "Booking", "Table" and "Customer.
My idea is to create a booking assigned to a table and a customer, the fields in the booking class is a Customer and a Table and the constructor assigns values to these field.
In my Table class i have a method that books the table "bookTable(Customer customer)" and sets the availablility to 'false'.
So my question is, is it good programming to call the method 'bookTable()' in the table class from the constructor of the Booking class? Or should i do it in another way?
Edited by: DJHingapus on Jul 6, 2009 5:12 AM

This sounds the wrong way around. What is the return value of bookTable(Customer)?
I'd expect it to return a Booking object that it creates.
Generally, you want the constructor to do as little as possible (while still only ever returning in a valid state, of course!).
The problem you can get when you call other methods is that you introduce the possibility of other objects getting access to your object before the constructor has finished running (i.e. before the object is completely initialized). This can lead to nasty problems that are hard to find and debug.

Similar Messages

Calling a method of one class from another withing the same package

hi,
i've some problem in calling a method of one class from another class within the same package.
for eg. if in Package mypack. i'm having 2 files, f1 and f2. i would like to call a method of f2 from f1(f1 is a servlet) . i donno exactly how to instantiate the object for f2. can anybody please help me in this regard.
Thank u in advance.
Regards,
Fazli

This is what my exact problem.
i've created a bean (DataBean) to access the database. i'm having a servlet program (ShopBook). now to check some details over there in the database from the servlet i'm in need to use a method in the DataBean.
both ShopBook.java and DataBean.java lies in the package shoppack.
in ShopBook i tried to instantiate the object to DataBean as
DataBean db = new DataBean();
it shows the compiler error, unable to resolve symbol DataBean.
note:
first i compiled DataBean.java, it got compiled perfectly and the class file resides inside the shoppack.
when i'm trying to compile the ShopBook its telling this error.
hope i'm clear in explaining my problem. can u please help me?
thank u in advance.
regards,
Fazli

Calling a method in Runnable Class

Hello I am trying to water this down but how can I call a method in my class
If I am passed only thread t.
MyClass mc = new MyClass();
Thread t = new Thread(mc);
t.start(); //works because it is a method of Thread
t.myMethodInMyClass (); // wont work because it cant find it
I have attempted casting to MyClass but I get CCException.
Any help would be wonderful..
cheers and thanks in advance.
Scott

Well, you could potentially have too many things in one class. You may want to try and modularize your classes more. But 'if in several situations [you] need different things to run'... well, the logic is just going to have to be there for that in some form.
Now, if you've already performed the logic to determine what to run and you are going to have to perform the logic again (in your run() method), then there is a flaw in your design.

How do i call the method in a class using servlet

i am doing a project which need to use servlet to call a few methods in a class and display those method on the broswer. i tried to write the servlet myself but there are still some errors .. can anyone help:
The servlet i wrote :
package qm.minipas;
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class test extends HttpServlet {
Database database;
/** Initializes the servlet.
public void init(ServletConfig config) throws ServletException {
super.init(config);
database = FlatfileDatabase.getInstance();
/** Destroys the servlet.
public void destroy() {
/** Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
* @param request servlet request
* @param response servlet response
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException {
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet</title>");
out.println("</head>");
out.println("<body>");
out.println("this is my class wossname"+FlatfileDatabase.getInstance()); // this is calling the toString() method in the instance of myJavaClass
out.println("this is my method"+FlatfileDatabase.getAll());
out.println("</body>");
out.println("</html>");
out.close();
/** Handles the HTTP <code>GET</code> method.
* @param request servlet request
* @param response servlet response
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException {
processRequest(request, response);
/** Handles the HTTP <code>POST</code> method.
* @param request servlet request
* @param response servlet response
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException {
processRequest(request, response);
/** Returns a short description of the servlet.
public String getServletInfo() {
return "Short description";
my methods which i need to call are shown below:
public Collection getAll() {
return Collections.unmodifiableCollection(patientRecords);
public Collection getInpatients() {
Collection selection=new ArrayList();
synchronized(patientRecords) {
for(Iterator i=patientRecords.iterator(); i.hasNext();) {
PatientRecord next=(PatientRecord) i.next();
if(next.isInpatient())
selection.add(next);
return Collections.unmodifiableCollection(selection);
public Collection getByAdmissionDate(Date dateOfAdmission) {
List selection=new ArrayList();
for(Iterator i=patientRecords.iterator(); i.hasNext();) {
PatientRecord next=(PatientRecord) i.next();
if(dateOfAdmission.equals(next.getDateOfAdmission()))
selection.add(next);
return Collections.unmodifiableCollection(selection);
public Collection getByAdmissionDates(Date from,Date to)
throws IllegalArgumentException {
if(to.before(from))
throw new IllegalArgumentException("End date must not be before start date");
List selection=new ArrayList();
for(Iterator i=patientRecords.iterator(); i.hasNext();) {
PatientRecord next=(PatientRecord) i.next();
Date nextAD=next.getDateOfAdmission();
if((nextAD.after(from)||nextAD.equals(from))
&&(nextAD.before(to)||nextAD.equals(to)))
selection.add(next);
return Collections.unmodifiableCollection(selection);
public Collection getByDischargeDates(Date from,Date to)
throws IllegalArgumentException {
if(to.before(from))
throw new IllegalArgumentException("End date must not be before start date");
List selection=new ArrayList();
for(Iterator i=patientRecords.iterator(); i.hasNext();) {
PatientRecord next=(PatientRecord) i.next();
Date nextAD=next.getDateOfDischarge();
if(nextAD==null)
continue;
if((nextAD.after(from)||nextAD.equals(from))
&&(nextAD.before(to)||nextAD.equals(to)))
selection.add(next);
return Collections.unmodifiableCollection(selection);
public Collection getByConsultant(String consultant) {
List selection=new ArrayList();
for(Iterator i=patientRecords.iterator(); i.hasNext();) {
PatientRecord next=(PatientRecord) i.next();
if(consultant.equalsIgnoreCase(next.getConsultant()))
selection.add(next);
return Collections.unmodifiableCollection(selection);
public Collection getByDischargeDate(Date dateOfDischarge) {
List selection=new ArrayList();
for(Iterator i=patientRecords.iterator(); i.hasNext();) {
PatientRecord next=(PatientRecord) i.next();
if(dateOfDischarge.equals(next.getDateOfDischarge()))
selection.add(next);
return Collections.unmodifiableCollection(selection);
public Collection getBySurname(String surname) {
List selection=new ArrayList();
for(Iterator i=patientRecords.iterator(); i.hasNext();) {
PatientRecord next=(PatientRecord) i.next();
if(surname.equalsIgnoreCase(next.getSurname()))
selection.add(next);
return Collections.unmodifiableCollection(selection);
public Collection getByWard(String ward) {
List selection=new ArrayList();
for(Iterator i=patientRecords.iterator(); i.hasNext();) {
PatientRecord next=(PatientRecord) i.next();
if(ward.equalsIgnoreCase(next.getWard()))
selection.add(next);
return Collections.unmodifiableCollection(selection);

please provide a detail description of your errors.

Calling a method and setting an ImageIcon with source from anoth class

I am trying to make a simple game, first I am trying to set up a game board, and make it possible to place units on the board. (This game will probably never be possible to play, I am just using it to try to understand Java, GUI, Swing, and using more than one class).
So far I have 4 classes: Board (extends JFrame, sets up a gameboard, on which to place the pieces), Unit (a class from which the specific units types will inherit), Horse (my only type of unit, which extends the Unit class), and Game (which calls methods from the other classes).
(These don't do much now.. this is what they will do, hopefully).
All these classes are in a package called Gamev1.
In the main method of Game, I do:
---code--
public static void main (String[]args){
new Board().show();
Horse horseUnits[] = new Horse[1];
horseUnits[0] = new Horse();
horseUnits[0].moveUnit(squares[0]);
end of code--
when I debug it I get:
myjava/FirstGraphics/Gamev1/Game.java [25:1] cannot resolve symbol
symbol: variable squares
location: class.myjava.FirstGraphics.Gamev1.Game
horseUnits[0].moveUnitsquares[0]);
1 error
---code----
moveUnit(JLabel moveTo)
is a method in Unit class:
public void moveUnit(JLabel moveTo){
target=moveTo;
target.setIcon(this.image);
if (this.position !=null)
this.position.setIcon(noUnit);
this.position=moveTo;
---end of code---------
squares[] is an array of JLabels which is set up in the Board class, whenever a new Board is created:
---code---
JLabel squares[] = new JLabel[100];
for (int s=0; s<100; s++){
squares[s] = new JLabel();
---end of code---
I tried changing the reference from squares[0] to Board.squares[0] but I got the same error message in debug.
Any idea what is wrong?
I have another problem, which is probably similar.
in the Board class I call:
squares[s].setIcon(Unit.noUnit);
and in the Unit class I have:
static ImageIcon noUnit = new ImageIcon("images//none.gif");
I don't get an error message mentioning it, but (without the attempt to place the horse on the board) the program compiles, but doesn't put this image on the labels. Any idea what is the porblem here?
If I have not given enough information for anyone to help me, please tell me what further information I should give.
Thanks to anyone who answers.

I got it to work with
    Board board = new Board();
    horseUnits[0].moveUnit(board.squares[0]);To use Board.squares[0], squares would have to be static.
The ImageIcon seemed to work okay. I noticed that your post had two slashes in the url [/] - that might throw things off . . .
The code below has the icon call at the end of setLabeLProperties.
I got carried away playing with the graphics so the squares don't work very well.
import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
public class HumaniBlue {
public static void main(String[] args) {
    Board board = new Board();
    board.show();
    JLabel label5 = board.getLabel(5);
    //System.out.println("label5 name = " + label5.getText());
    Horse[] horseUnits = new Horse[1];
    horseUnits[0] = new Horse();
    horseUnits[0].moveUnit(board.squares[0]);
class Unit {
static ImageIcon noUnit = new ImageIcon("images/bclynx.jpg");
public void moveUnit(JLabel square) {
class Horse extends Unit {
public Horse() {}
class Board {
JFrame f;
JPanel gameBoard;
int labelSize;
JLabel[] squares = new JLabel[16];
GridBagConstraints gbc = new GridBagConstraints();
public Board() {
    gameBoard = new JPanel(new GridBagLayout()) {
      public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        double width = getSize().width;
        double height = getSize().height;
        g2.setPaint(Color.white);
        g2.fill(new Rectangle2D.Double(0, 0, width, height));
        g2.setPaint(Color.black);
        Shape line;
        double
          gridSize = (width < height ? width : height) * 0.8,
          gridUnit = (width < height ? width : height) / 5,
          x = (width - gridSize) / 2,
          y = (height - gridSize) / 2;
        labelSize = (int)gridUnit;
        for(int j = 0; j < 5; j++) {
          line = new Line2D.Double(x, y, x, y + gridSize);
          g2.draw(line);
          x += gridUnit;
        x = (width - gridSize) / 2;
        for(int j = 0; j < 5; j++) {
          line = new Line2D.Double(x, y, x + gridSize, y);
          g2.draw(line);
          y += gridUnit;
      //System.out.println("width = " + width + "\theight = " + height + "\n" +
      //                   "x = " + x + "\ty = " + y + "\n" +
      //                   "gridSize = " + gridSize + "\tgridUnit = " + gridUnit);
    f = new JFrame();
    f.getContentPane().add(gameBoard);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setSize(400,400);
    f.setLocation(600,200);
    //f.setVisible(true);
    setLabelProperties();
private void setLabelProperties() {
    int
      r   = 30,
      g   = 30,
      b   = 0,
      inc = 55;
    //System.out.println("labelSize = " + labelSize);
    for(int j = 0; j < squares.length; j++) {
      squares[j] = new JLabel("Square " + j, JLabel.CENTER);
      squares[j].setOpaque(true);
      squares[j].setPreferredSize(new Dimension(73, 73));
    // add labels
    int index = 0;
    gbc.gridx = 0;
    gbc.gridy = 0;
    for(int y = 0; y < 4; y++) {
      for(int x = 0; x < 4; x++) {
        index = y * 4 + x;
        squares[index].setBackground(new Color(r,g,b,90));
        gameBoard.add(squares[index], gbc);
        gbc.gridx++;
        r += inc;
      gbc.gridy++;
      gbc.gridx = 0;
      r = 90;
      g += inc;
    squares[9].setIcon(Unit.noUnit);
public void show() {
    f.setVisible(true);
public JLabel getLabel(int index) {
    return squares[index];
}

Calling a Method in other Class

I want to call a method in another class when an action is preformed can anyone suggest how I might do this??
     addSquare.addActionListener(new ActionListener()
               public void actionPerformed(ActionEvent e)


I want to call a method in another class when an
action is preformed can anyone suggest how I might do
this??
        addSquare.addActionListener(new ActionListener()
             public void actionPerformed(ActionEvent e)
             {               OtherClass oc = //getrefererncetootherclass
               oc.methodtocall(params, to, pass);

Calling a method from abstarct class

Hi Experts,
Am working on ABAP Objects.
I have created an Abstract class - with method m1.
I have implemented m1.
As we can not instantiate an abstract class, i tried to call the method m1 directly with class name.
But it it giving error.
Please find the code below.
CLASS c1 DEFINITION ABSTRACT.
PUBLIC SECTION.
    DATA: v1 TYPE i.
    METHODS: m1.
ENDCLASS.                    "c1 DEFINITION
CLASS c1 IMPLEMENTATION.
METHOD m1.
    WRITE: 'You called method m1 in class c1'.
ENDMETHOD. "m1
ENDCLASS.                    "c1 IMPLEMENTATION
CALL METHOD c1=>m1.
Please tell me what is wrong and how to solve this problem.
Thanks in Advance.

Micky is right, abstract means not to be instantiated. It is just a "template" which you can use for all subsequent classes. I.e you have general abstract class vehicle . For all vehicles you will have the same attributes like speed , engine type , strearing , gears etc and methods like start , move etc.
In all subsequent classes (which inherit from vehicle) you will have more specific attributes for each. But all of these classes have some common things (like the ones mentioned above), so they use abstract class to define these things for all of them.
Moreover there is no sense in creating instance (real object) of class vehicle . What kind of physical object would vehicle be? there is no such object in real world, right? For this we need to be more precise, so we create classes which use this "plan" for real vehicles. So the abstract class here is only to have this common properties and behaviour defined in one place for all objects which will have these. Abstract object however cannot be created per se. You can only create objects which are lower in hierarchy (which are specific like car , ship, bike etc).
Hope this claryfies what we need abstract classes for.
Regards
Marcin

Calling a method in a class extended from thread

I'm trying to use two threads of type ThreadTest to call the addNum method in the class below. I found that i couldnt call the addnum method with the instances I created but had to make the addnum method static and then call it with the class name ThreadTest.Is there anyway to get round this? i'm doing this exercise to try and understand synchronisation. Thanks
import java.lang.Thread;
import java.util.*;
class ThreadTest extends Thread implements Runnable{
     private int x;
     private static ArrayList intnumbers = new ArrayList();
     public ThreadTest(int no)
          x=no;
     public void run()
          for (int i=0; i<x; i++)
               try
               System.out.println(i);
               Thread.currentThread().sleep((long)(Math.random() * 1000));
          }catch(InterruptedException e ){e.getMessage();}
     public static void addNum(int n)
          synchronized(intnumbers){
                    intnumbers.add(new Integer(n));
public static void main(String[] args)
     Thread testThread = new Thread(new ThreadTest(50));
     Thread testThreadb = new Thread(new ThreadTest(50));
     testThread.start();
     testThreadb.start();
          ThreadTest.addNum(10);
    //*** this gives an error
    //testThread.addNumber(10);
    //testThreadb.addNumber(10);
}

ok here goes again. ;).
import java.lang.Thread;
import java.util.*;
class ThreadTest extends Thread implements Runnable{
     private int x;
     private static ArrayList intnumbers = new ArrayList();
     public ThreadTest(int no)
          x=no;
     public void run()
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               try
               System.out.println(i);
               Thread.currentThread().sleep((long)(Math.random() * 1000));
          }catch(InterruptedException e ){e.getMessage();}
     public static void addNum(int n)
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public static void main(String[] args)
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//works ok but I want to call addNum with 2 different threads
     ThreadTest.addNum(10);
}

Calling a method from custom Class in WD Application

Hi,
I wrote a piece of code in method SEARCH for my WD Application.
Instead of diectly callling the method I would like to create a class and then call the method.
How do we proceed?
Do we use SE24 first or can we start creating class from WD application itself?
Rgds
vara

Hi Vara,
Either way it is possible if you are creating from web dynpro then you can create assistance class from component properties there you can write one method and to access that method always you have an instance wd_assist.
From se24 create a class and declare a method. if you declare level of method is instance then you have to create object first in application and then access your method using created instance.

Call a method of a class file from an Applet

I have an Applet nmaed CountDown.java in which I have to call a method "doSelect" of a class file named DBConnection.java. How do I do this? Both the Applet and the class file are in the same directory.

You should put both classes in the same package and create a jar file containing the whole package.
Make sure the DBConnection class is public or protected and that the method you're trying to call is public or protected.

How to call main method in one class from another class

Suppose i have a code like this
class Demo
public static void main(String args[])
System.out.println("We are in First class");
class Demo1
public static void main(String args[])
System.out.println("We are in second class");
In the above program how to call main method in demo calss from Demo1 class......???????

No, i dont know how to call other than main methods from other classes
And one more doubt i have i.e. Like in C can we see the execution of the program like how the code is being compiled step by step and how the value of the variable changes from step to step like(Add Watch).........

How to call particular method in action class from Portlets StrutsContent

I am developing a web application which uses weblogic portlets and struts. This is what I have for now in the .portlet file.
+<netuix:strutsContent action="getStudentList" module = "people/students"+
refreshAction = "getStudentList" reqestAttrpersistence="none"/>
I want it to change something like this:
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refreshAction = "getStudentLis.do?method=allGrads" reqestAttrpersistence="none"/>
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Thanks
Edited by: user13634949 on Jun 23, 2011 1:22 PM
Edited by: user13634949 on Jun 23, 2011 1:22 PM

No, i dont know how to call other than main methods from other classes
And one more doubt i have i.e. Like in C can we see the execution of the program like how the code is being compiled step by step and how the value of the variable changes from step to step like(Add Watch).........

How to call a method of a class where the name of method is string

i have a method of a class in the form of a string and i have the object of the class to which it belongs .what i want to do is call this method.
for ex:
S1 s=new S1();
// this is the object of my class. this class has one method called executeMe()
String methodname="executeMe";
//i have the name of the method with me in the form of string.
so how can i call the class's method in this scenario from the string like what should i write in sucha way that i get s.executeMe(); it is not presumed that this will only be the method that will be called. there maybe some other method too and it has also to be called this way. so please guide.

S1 s = new S1();
String name = "executeMe";
Method m = s.getClass().getDeclaredMethod(name,null); // no parameters
m.invoke(s,null);Built from memory, maycontain flaws.

How to call a method in IMPL class from one context node

Hi, I´ve been only study the posibility to access a method in the IMPL class from one context node class...CN## without using events, is there a way to call it ??? I don´t have it as requierement just learning thanks !.

Hi,
Try this by following this you can get the custom controller instacne in the view context nodes, for your requirement you can keep the view implementation class instance instead of cuco..
To get the custom controller instance in Context node getter/setter method:
1. Declare Cuco instance reference variable in ctxt class..
2. Set this cuco ref. in the Create context node method of ctxt class:
try.
gr_cucoadminh ?= owner->get_custom_controller( 'ICCMP_BTSHEAD/cucoadminh' ). "#EC NOTEXT
catch cx_root.
endtry.
you can avoid this step as this is not needed in case of view isntance
3. Assign this instance to the respective context node Create method using:
BTStatusH->gr_cuco ?= gr_cucoadminh. " here assign the view implementation ref. " me" instead of gr_cucoadminh
Here gr_cuco is the ref. variable of custom controller in the respective context node for eg. BtstatusH
Sample implementation of this can be found in
ICCMP_BTSHEAD/BTSHeader ->context node BTACTIVITYH-> attr ->GR_CUCO(instance of cuco)
Cheers,
Sumit Mittal

Calling main method of a class

Hi
I have to call the Main method of a class in some other class becuass that class is accepting command line aurguments.
I test it and everything is working fine.
           String[] strings = new String[3];
           strings[0] = "E:/practice.cap";
           strings[1] = "-o";
           strings[2] = "E:/practice.txt";
           Main.main(strings);I now want to know is there any drawback of doing this ?
BR
regards

Muhammad Umer wrote:
Good Explanation. But my question is not to explain the importance of main method in classes :)As far as the Java language and APIs go, there's nothing wrong with calling main just like any other method, because it is just another method. It's only special to the JVM, and to programmers who assume that it's the entry point to the program.
As far as Java is concerned, you can call as many mains as you want. The only potential problem arises if some particular main is written in a way that relies on it being the entry point to the whole program. That is, if the author wrote it with the assumption that it would only be called by the JVM at startup time, and would not be called arbitrarily from within your code (EDIT: and if proper behavior relies on that assumption being upheld). However, this is just a particular case of a general issue that we always have to be aware of, namely, make sure you understand how a method is intended to be used, and use it in that fashion, or accept the consequences.
EDIT: However, having said that, it's unusual to call main explicitly, so if you can, I would suggest pulling the functionality that you want out of that main into a different method, and then both your code and the main can call that method. If you cannot do that, then at the point where you call main, clearly document why you're doing it. Otherwise, whoever reads the code a few months or years from now--maybe somebody else, maybe you--will be wondering if the programmer really knew what he was doing, or if that is a mistake. That kind of second-guessing is the source of a lot of maintenance nightmares.
Edited by: jverd on Nov 3, 2011 8:43 AM

How to call a method from a class without creating an instance fromthisclas

I want to create a class with methods but I want to call methods from this class without creating an instance from this class. Is this possible?
Is there in Java something like class methods and object methods????

keyword 'static' my friend.
public class foo {
public static void bar {
System.out.println ("hello");
foo.bar()

Call a method of a class in a constructor of another class?

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