Public main method in a non-public class

Hi,
It is said that main method in a java class must be public so that it can be invoked by JVM. This works even if the class itself has default modifier.
But while programming, any method (be it public) of a class with default access modifier from one package can't be accessed by classes from other packages. For example,
1. Consider class A in package a.
package a;
class A {
public void methA() {}
2. Now consider class B in pakage b.
package b;
class B {
void methB() {
// Here it can't access class A and its method methA()
So how does JVM invoke the main method of a class with default access modifier. Assume that the class is in some package a.b.c
Regards,
Amit

Hi,
Maybe this can also be beneficial for you.
Standalone applications don't necessarily have init and start methods. They must have a public static void main routine to start things off. The main routine typically creates some object of the master class. It can't use any non-static variables or methods in the class with the implied this, since there is no this object. It typically quickly returns. Then the event loop processing starts. Even the static main method must live inside some public class, or at least in the top class, the first class and the class for whom the source file is named. There are no such thing as standalone static methods in Java. The signature of the main class must look exactly like this. Cut and paste it to be sure:

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How to add a code TestIfElse(10) to the Main method of the Program.cs class?

How to add a code TestIfElse(10) to the Main method of the Program.cs class?
Here is my code and I have copied from the Wiley book for Microsoft certification page 14,
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ifelse_Statement
class Program
static void Main(string[] args);
TestIfElse(10);
public static void TestIfElse(int n);
if(n < 10)
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Console. WriteLine("n is greater than or equal to 30");
Here is the error list I am getting,
Error 1 Method must have a return type C:\Users\PVS\documents\visual studio 2013\Projects\Lesson01\switch_Statement\Program.cs
12 13
switch_Statement
Error 2
Type expected C:\Users\PVS\documents\visual studio 2013\Projects\Lesson01\switch_Statement\Program.cs
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Error 10
Type or namespace definition, or end-of-file expected
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Error 12
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static void Main(string[] args){
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public static void TestIfElse(int n)
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Console.WriteLine("n is less than 10");
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Fouad Roumieh

"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.

How do I bring array into main method from class?

Can someone help?
If I add data to an array in a class. Then how do I bring it into the main method?
I instantiate the class in the main method.
Then I am not sure. Can some one comment and maybe show a short example?
Thanks

A catch,
try {
// Some code
} catch (Exception e) {
}...should be where you call a method trowing a particular exception.
Example:
try {
// parseInt(String value) throws NumberFormatException
int number = Integer.parseInt(string_value);
} catch (NumberFormatException e) {
/Andrew

Retrieve ServletContext from non-servlet class

A servlet calls a method which is located in another class which is not a servlet. Within this method of the non-servlet class, i need to access the ServletContext of the servlet that has called the method. What i am currently doing is simply passing the ServletContext as a parameter to the method.
I would like to avoid passing the ServletContext all the time, so i'm wondering if it's possible, from the non-servlet class, to retrieve the ServletContext of the servlet which has called the method of the non-servlet class.

Thanks J-Fine, that's a smart suggestion. BTW in the meantime i figured out that passing the ServletContext is not that bad idea, after all it reflects the structure of the app. However if i'll change my mind again i'll do like you suggested.

Are there non-public classes in Java SDK?

Or are ALL classes in all packages of the Java SDK public?
I have looked in the sources spot checking and didn't find a non public (default) class.
If all classes are public, why?
There exists a means in Java language to define a class as default ("class MyClass" instead of "public class MyClass") visibility. So why isn't it used by Java SDK (if this is really true)?

I dont know what language you're programming in.
If you don't specify
public class
or
private class
the class is "protected".
Read the spec.If you read the spec, you'll see that, with respect to a class:
(per section 6.6.2) Classes from outside the package the class lives in that extend the class have access to protected members.
(per section 6.6.5) Classes from outside the package this thing lives in that extend this class do not have access to default members.
Relevant part of section 6.6.5 (Example: Default-Access Fields, Methods, and Constructors) is:
If none of the access modifiers public, protected, or private are specified, a class member or constructor is accessible throughout the package that contains the declaration of the class in which the class member is declared, but the class member or constructor is not accessible in any other package.
This is default access, not protected access
Lee

Calling public class method from the servlet dopost() implementation

Hi!
My application is a simple application where i wrote a JSP page to enter the USERNAME and PASSWORD. And this JSP will call a HttpServlet
with in which i am calling another Java class ValidateUser which will check aginst the Oracle Database table whether that Username and password combination exists and returns the user's name.
But when i am trying to call that method is throwing me an error. here is the typical code i wrote.
servlet
package isispack;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import java.io.*;
public class Login extends HttpServlet{
public void doPost(HttpServletRequest req, HttpServletResponse res)
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String userId = req.getParameter("user_id");
String password = req.getParameter("user_pass");
// if uName is null .. user is not authorized.
String uName = Validate(userId, password);
and
Validate class
package isispack;
import java.sql.*;
import java.util.*;
import java.lang.*;
public class ValidateUser
public String ValidateUser(String inputUserid, String inputPwd) throws
SQLException{
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The ERROR
Error(18,18): method ValidateUser(java.lang.String, java.lang.String) not found in class isispack.Login
One more thing i forgot to tell you. I am trying to run this application on JDeveloper. Please helpme out if you can . Thank you.
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OK! I made it static method
and tried to call the method as follows
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even if i create the instence and
ValidateUser Validate;
then call
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In either case is giving me the following error.Tarun, am new to Java programming, please help me out. And can you please tell me where can i find things in consise to brush up my fundamentals?.
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Track public classes, interfaces and methods by ID

Hi All,
I'm wondering whether there is a tool to assign a unique ID to classes, interfaces and methods (eg. within Javadoc) and track these IDs.
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Does anybody know of such a tool (commercial or not)?
Thanks,
Daniel

I'm a bit confused as to whether or not I understand you correctly. Please tell me if the following pseudocode is somewhat like the solution you are looking for:
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    *   Returns true if the method is used for the specified
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   public String getMethodSignature() {
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   public int[] getCoverage() {
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class ClassFunctionality {
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   private List classFunctions;
   public MethodFunctionality getMethodDetails(String methodSignature) {
      return (MethodFunctionality) this.methodDetails.get(methodSignature);
    *   Returns true if the class is used for the specified
    *   requirement, false otherwise.
   public boolean fulfills(int requirementId) {
      if classFunctions.contains(requirementId)
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    *   Returns an array with IDs of each functional
    *   requirement covered by the class.
   public int[] getCoverage() {
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}Mapping classes and methods to functionality like this would both allow you to query each class and method for all the functional requirements they claim to cover and would allow you to collect all classes and methods involved for a particular functional requirement.

Question about access non-public class from other package.

Hi, everyone!
Suppose class A and class B are in the same java file of package pkg1
-- A.java. So, A is a public class and B is a non-public class.
If I want to access class B from another class class C and class
C is in package pkg2. When compiling, an error occurs indicating
that class B is not visible to class C.
So, If I defined serveral classes in one java file and I want to
access every class from other package. How should I do?
(I think in one java file, there should be only one public class and
only the public class can be accessed from other package.)
Thanks in advance,
George

So, If I defined serveral classes in one java file and
I want to
access every class from other package. How should I
do? As you already seem to know, there is at most one public class allowed per source file (at least, with javac and most popular compilers). So if you want more than one public class, you will need to use more than one file...

Main method not found and how to put event handlers in an inner class

How would I put all the event handling methods in an inner class and I have another class that just that is just a main function, but when i try to run the project, it says main is not found. Here are the two classes, first one sets up everything and the second one is just main.
mport java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
public class JournalFrame extends JFrame {
private JLabel dateLabel = new JLabel("Date: ");
private JTextField dateField = new JTextField(20);
private JPanel datePanel = new JPanel(new FlowLayout());
BorderLayout borderLayout1 = new BorderLayout();
JPanel radioPanel = new JPanel();
JPanel statusPanel = new JPanel();
JPanel textAreaPanel = new JPanel();
JPanel buttonPanel = new JPanel();
GridLayout gridLayout1 = new GridLayout();
FlowLayout flowLayout1 = new FlowLayout();
GridLayout gridLayout2 = new GridLayout();
GridLayout gridLayout3 = new GridLayout();
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JTextArea entryArea = new JTextArea();
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JButton saveButton = new JButton();
ButtonGroup entryType = new ButtonGroup();
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try {
jbInit();
catch(Exception e) {
e.printStackTrace();
private void initWidgets(){
private void jbInit() throws Exception {
this.getContentPane().setLayout(borderLayout1);
radioPanel.setLayout(gridLayout1);
statusPanel.setLayout(flowLayout1);
textAreaPanel.setLayout(gridLayout2);
buttonPanel.setLayout(gridLayout3);
personalButton.setSelected(true);
personalButton.setText("Personal");
personalButton.addActionListener(new JournalFrame_personalButton_actionAdapter(this));
businessButton.setText("Business");
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entryArea.setText("");
entryArea.setColumns(10);
entryArea.setLineWrap(true);
entryArea.setRows(30);
entryArea.setWrapStyleWord(true);
clearButton.setPreferredSize(new Dimension(125, 25));
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clearButton.addActionListener(new JournalFrame_clearButton_actionAdapter(this));
saveButton.setText("Save Journal Entry");
saveButton.addActionListener(new JournalFrame_saveButton_actionAdapter(this));
this.setTitle("Journal");
gridLayout3.setColumns(1);
gridLayout3.setRows(0);
this.getContentPane().add(datePanel, BorderLayout.NORTH);
this.getContentPane().add(radioPanel, BorderLayout.WEST);
this.getContentPane().add(textAreaPanel, BorderLayout.CENTER);
this.getContentPane().add(buttonPanel, BorderLayout.EAST);
entryType.add(personalButton);
entryType.add(businessButton);
datePanel.add(dateLabel);
datePanel.add(dateField);
radioPanel.add(personalButton, null);
radioPanel.add(businessButton, null);
textAreaPanel.add(entryArea, null);
buttonPanel.add(clearButton, null);
buttonPanel.add(saveButton, null);
this.getContentPane().add(statusPanel, BorderLayout.SOUTH);
statusPanel.add(status, null);
this.pack();
setDefaultCloseOperation(EXIT_ON_CLOSE);
private void saveEntry() throws IOException{
if( personalButton.isSelected())
String file = "Personal.txt";
BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
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bw.write(entryArea.getText());
bw.newLine();
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bw.flush();
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entryArea.setText("");
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public class JournalApp {
public static void main(String args[])
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Bet you're trying "java JournalFrame" when you need to "java JournalApp".
Couple pointers toward good code.
1) Use white space (extra returns) to separate your code into logical "paragraphs" of thought.
2) Add comments. At a minimum a comment at the beginning should name the file, state its purpose, identify the programmer and date written. A comment at the end should state that you've reached the end. In the middle, any non-obvious code should be commented and closing braces or parens should have a comment stating what they close (if there is non-trivial separation from where they open).
Here's a sample:
// JournalFrame.java - this does ???
// saisoft, 4/18/03
// constructor
private void jbInit() throws Exception {
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// end JournalFrame.java3) What would you expect to gain from that inner class? It might be more cool, but would it be more clear? I give the latter (clarity) a lot of importance.

Problem with constructors and using public classes

Hi, I'm totally new to Java and I'm having a lot of problems with my program :(
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continue;
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public static void main (String args[])
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for(int i=0; i<args.length; i++)
Prime(i);}

I've made changes and now my code looks like this:
public class ESieve {
ESieve(int n) {
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public static boolean sieve(int n)
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for(int i=2;i*i<n;i++){
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if (x=true)
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int n; int i, j;
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It shows an error for main:
{quote} ESieveTest.java:21: '.class' expected
int maximum=max(args[]); {quote}
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Class extending a Frame with main method in it - how do I use the methods?

Howdy.
Having a problem.. I want my "main" class, ie. the class with the main method in it to extend a Frame class.. because the main method is static, I can't use Frame's methods.
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When I use Forte to make a Frame program it sets up a constructor/etc. for the main class and then it does something akin to this (the class is called MazeGenerator) :
public static void main(String args[]) {
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Ta.
- Scutt.

Create an instance of the frame in main then the constructor can control it. Or you could add an init method or something:
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Calling main method in another class using command line arguements

Hi
My program need to use 4 strings command line arguments
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java programming for beginners // arguments
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So the output wil be
java
programming
for
beginners
import java.lang.*;
public class First extends Second{
public static void main(String[] args) {
for(int i = 0; i < args.length; i++){
Second.main(args); // Error I think
import java.lang.*;
public class Second {
public static void main(String[] args){
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Your style looks quite bad for starters..... Hows
this://import java.lang.*; /* NOT NEEDED */
public class First extends Second{
public First(String s) {
super(s);
public static void main(String[] args) {
for(int i = 0; i < args.length; i++){
new First(s);
public class Second {
public Second(String s)
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NOT NEEDED:
public static void main(String[] args){
System.out.println(args[0]);
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How would I put all the event handling methods in an inner class and I have another class that just that is just a main function, but when i try to run the project, it says main is not found. Here are the two classes, first one sets up everything and the second one is just main.
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JLabel status = new JLabel();
JTextArea entryArea = new JTextArea();
JButton clearButton = new JButton();
JButton saveButton = new JButton();
ButtonGroup entryType = new ButtonGroup();
public JournalFrame(){
try {
jbInit();
catch(Exception e) {
e.printStackTrace();
private void initWidgets(){
private void jbInit() throws Exception {
this.getContentPane().setLayout(borderLayout1);
radioPanel.setLayout(gridLayout1);
statusPanel.setLayout(flowLayout1);
textAreaPanel.setLayout(gridLayout2);
buttonPanel.setLayout(gridLayout3);
personalButton.setSelected(true);
personalButton.setText("Personal");
personalButton.addActionListener(new JournalFrame_personalButton_actionAdapter(this));
businessButton.setText("Business");
status.setText("");
entryArea.setText("");
entryArea.setColumns(10);
entryArea.setLineWrap(true);
entryArea.setRows(30);
entryArea.setWrapStyleWord(true);
clearButton.setPreferredSize(new Dimension(125, 25));
clearButton.setText("Clear Journal Entry");
clearButton.addActionListener(new JournalFrame_clearButton_actionAdapter(this));
saveButton.setText("Save Journal Entry");
saveButton.addActionListener(new JournalFrame_saveButton_actionAdapter(this));
this.setTitle("Journal");
gridLayout3.setColumns(1);
gridLayout3.setRows(0);
this.getContentPane().add(datePanel, BorderLayout.NORTH);
this.getContentPane().add(radioPanel, BorderLayout.WEST);
this.getContentPane().add(textAreaPanel, BorderLayout.CENTER);
this.getContentPane().add(buttonPanel, BorderLayout.EAST);
entryType.add(personalButton);
entryType.add(businessButton);
datePanel.add(dateLabel);
datePanel.add(dateField);
radioPanel.add(personalButton, null);
radioPanel.add(businessButton, null);
textAreaPanel.add(entryArea, null);
buttonPanel.add(clearButton, null);
buttonPanel.add(saveButton, null);
this.getContentPane().add(statusPanel, BorderLayout.SOUTH);
statusPanel.add(status, null);
this.pack();
setDefaultCloseOperation(EXIT_ON_CLOSE);
private void saveEntry() throws IOException{
if( personalButton.isSelected())
String file = "Personal.txt";
BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
entryArea.getText();
bw.write("Date: " + dateField.getText());
bw.newLine();
bw.write(entryArea.getText());
bw.newLine();
bw.flush();
bw.close();
status.setText("Journal Entry Saved");
else if (businessButton.isSelected())
String file = "Business.txt";
BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
bw.write("Date: " + dateField.getText());
bw.newLine();
bw.write(entryArea.getText());
bw.newLine();
bw.flush();
bw.close();
status.setText("Journal Entry Saved");
void clearButton_actionPerformed(ActionEvent e) {
dateField.setText("");
entryArea.setText("");
status.setText("");
void saveButton_actionPerformed(ActionEvent e){
try{
saveEntry();
}catch(IOException error){
status.setText("Error: Could not save journal entry");
void personalButton_actionPerformed(ActionEvent e) {
class JournalFrame_clearButton_actionAdapter implements java.awt.event.ActionListener {
JournalFrame adaptee;
JournalFrame_clearButton_actionAdapter(JournalFrame adaptee) {
this.adaptee = adaptee;
public void actionPerformed(ActionEvent e) {
adaptee.clearButton_actionPerformed(e);
class JournalFrame_saveButton_actionAdapter implements java.awt.event.ActionListener {
JournalFrame adaptee;
JournalFrame_saveButton_actionAdapter(JournalFrame adaptee) {
this.adaptee = adaptee;
public void actionPerformed(ActionEvent e) {
adaptee.saveButton_actionPerformed(e);
class JournalFrame_personalButton_actionAdapter implements java.awt.event.ActionListener {
JournalFrame adaptee;
JournalFrame_personalButton_actionAdapter(JournalFrame adaptee) {
this.adaptee = adaptee;
public void actionPerformed(ActionEvent e) {
adaptee.personalButton_actionPerformed(e);
public class JournalApp {
public static void main(String args[])
JournalFrame journal = new JournalFrame();
journal.setVisible(true);
}

Here is the complete code (with crappy indentation) :
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
public class JournalFrame extends JFrame {
    private JLabel dateLabel = new JLabel("Date: ");
    private JTextField dateField = new JTextField(20);
    private JPanel datePanel = new JPanel(new FlowLayout());
    BorderLayout borderLayout1 = new BorderLayout();
    JPanel radioPanel = new JPanel();
    JPanel statusPanel = new JPanel();
    JPanel textAreaPanel = new JPanel();
    JPanel buttonPanel = new JPanel();
    GridLayout gridLayout1 = new GridLayout();
    FlowLayout flowLayout1 = new FlowLayout();
    GridLayout gridLayout2 = new GridLayout();
    GridLayout gridLayout3 = new GridLayout();
    JRadioButton personalButton = new JRadioButton();
    JRadioButton businessButton = new JRadioButton();
    JLabel status = new JLabel();
    JTextArea entryArea = new JTextArea();
    JButton clearButton = new JButton();
    JButton saveButton = new JButton();
    ButtonGroup entryType = new ButtonGroup();
    public JournalFrame(){
        try {
            jbInit();
        catch(Exception e){
            e.printStackTrace();
    private void initWidgets(){
    private void jbInit() throws Exception {
        this.getContentPane().setLayout(borderLayout1);
        radioPanel.setLayout(gridLayout1);
        statusPanel.setLayout(flowLayout1);
        textAreaPanel.setLayout(gridLayout2);
        buttonPanel.setLayout(gridLayout3);
        personalButton.setSelected(true);
        personalButton.setText("Personal");
        personalButton.addActionListener(new JournalFrame_personalButton_actionAdapter(this));
        businessButton.setText("Business");
        status.setText("");
        entryArea.setText("");
        entryArea.setColumns(10);
        entryArea.setLineWrap(true);
        entryArea.setRows(30);
        entryArea.setWrapStyleWord(true);
        clearButton.setPreferredSize(new Dimension(125, 25));
        clearButton.setText("Clear Journal Entry");
        clearButton.addActionListener(new JournalFrame_clearButton_actionAdapter(this));
        saveButton.setText("Save Journal Entry");
        saveButton.addActionListener(new JournalFrame_saveButton_actionAdapter(this));
        this.setTitle("Journal");
        gridLayout3.setColumns(1);
        gridLayout3.setRows(0);
        this.getContentPane().add(datePanel, BorderLayout.NORTH);
        this.getContentPane().add(radioPanel, BorderLayout.WEST);
        this.getContentPane().add(textAreaPanel, BorderLayout.CENTER);
        this.getContentPane().add(buttonPanel, BorderLayout.EAST);
        entryType.add(personalButton);
        entryType.add(businessButton);
        datePanel.add(dateLabel);
        datePanel.add(dateField);
        radioPanel.add(personalButton, null);
        radioPanel.add(businessButton, null);
        textAreaPanel.add(entryArea, null);
        buttonPanel.add(clearButton, null);
        buttonPanel.add(saveButton, null);
        this.getContentPane().add(statusPanel, BorderLayout.SOUTH);
        statusPanel.add(status, null);
        this.pack();
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    private void saveEntry() throws IOException{
        if( personalButton.isSelected()){
            String file = "Personal.txt";
            BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
            entryArea.getText();
            bw.write("Date: " + dateField.getText());
            bw.newLine();
            bw.write(entryArea.getText());
            bw.newLine();
            bw.flush();
            bw.close();
            status.setText("Journal Entry Saved");
        else if (businessButton.isSelected()){
            String file = "Business.txt";
            BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
            bw.write("Date: " + dateField.getText());
            bw.newLine();
            bw.write(entryArea.getText());
            bw.newLine();
            bw.flush();
            bw.close();
            status.setText("Journal Entry Saved");
    void clearButton_actionPerformed(ActionEvent e) {
        dateField.setText("");
        entryArea.setText("");
        status.setText("");
    void saveButton_actionPerformed(ActionEvent e){
        try{saveEntry();}catch(IOException error){
            status.setText("Error: Could not save journal entry");
    void personalButton_actionPerformed(ActionEvent e) {
    class JournalFrame_clearButton_actionAdapter implements java.awt.event.ActionListener {
    JournalFrame adaptee;
    JournalFrame_clearButton_actionAdapter(JournalFrame adaptee) {
        this.adaptee = adaptee;
    public void actionPerformed(ActionEvent e) {
        adaptee.clearButton_actionPerformed(e);
class JournalFrame_saveButton_actionAdapter implements java.awt.event.ActionListener {
    JournalFrame adaptee;
    JournalFrame_saveButton_actionAdapter(JournalFrame adaptee) {
        this.adaptee = adaptee;
    public void actionPerformed(ActionEvent e) {
        adaptee.saveButton_actionPerformed(e);
class JournalFrame_personalButton_actionAdapter implements java.awt.event.ActionListener {
    JournalFrame adaptee;
    JournalFrame_personalButton_actionAdapter(JournalFrame adaptee) {
        this.adaptee = adaptee;
    public void actionPerformed(ActionEvent e) {
        adaptee.personalButton_actionPerformed(e);
}BadLands

Can we call main method in another class?

Hi...
can we call main method in another class?
If no, please tell me the exact reason why can't we call that....

ok
can u give that code for me?
class A {
public static void main(String [] args){
System.out.println("In A");
class B {
public static void main(String [] args){
A.main(null);
}

Public main method in a non-public class

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