Having trouble with "main" method
I have just installed j2re1.4.1 and I am having trouble running my applications. Every time I try to run even the smallest of apps I get an error message about the "Main" method.
In textpad i get this message:
"Exception in thread "main" java.lang.NoClassDefFoundError:"
and in Jcreator I get this message:
"The system couldnt find a suitable main method"
what is going wrong?How can I fix this?
It could be something as simple as Case :-/
If you have a file Foo.java with a class Foo with a main()
you can compile it with javac foo.javawhich will create Foo.classbut you cannot run it with java fooyou will get Exception in thread "main" java.lang.NoClassDefFoundError: roids (wrong name: Foo)whereas java Foowill work just fine.
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Calculator: having problem with main method
This is a program that converts Infix expression to Postfix and evaluates it.I used eclipse to run this.
In my main method, how do i get it to loop? when the user still wants to input another expression? i just can't seem to figure this out.
import java.io.*;
import java.util.*;
import javax.swing.*;
public class Calculator {
private static Stack operators = new Stack();
private static Stack operands = new Stack();
private static int precedence( char operator ) {
if (operator == '+' || operator == '-' )
return 1;
else if (operator == '*' || operator == '/' || operator == '%')
return 2;
return 0;
private static String convertToPostfix( String infix ) {
StringTokenizer input = new StringTokenizer( infix );
String symbol;
String postfix = "";
while (input.hasMoreTokens()) {
symbol = input.nextToken();
if (Character.isDigit(symbol.charAt(0))){
postfix = postfix + " " + (Integer.parseInt(symbol));
}else if (symbol.equals("(")){
Character isOperator = new Character('(');
operators.push( isOperator );
}else if (symbol.equals(")")) {
while (((Character)operators.peek()).charValue() != '(') {
postfix = postfix + " " + operators.pop();
}operators.pop();
} else {
while (!operators.empty() && !(operators.peek()).equals("(") && precedence(symbol.charAt(0)) <= precedence(((Character)operators.peek()).charValue()))
postfix = postfix + " " + operators.pop();
Character isOperator = new Character(symbol.charAt(0));
operators.push( isOperator );
while (!operators.empty())
postfix = postfix + " " + operators.pop();
return postfix;
private static int evaluate( String postfix ) {
StringTokenizer input2 = new StringTokenizer( postfix );
int value;
String symbol;
while (input2.hasMoreTokens()) {
symbol = input2.nextToken();
if (Character.isDigit(symbol.charAt(0))) {
Integer isOperand = new Integer(Integer.parseInt(symbol));
operands.push( isOperand );
}else{
int op2 = ((Integer)operands.pop()).intValue();
int op1 = ((Integer)operands.pop()).intValue();
int result = 0;
switch(symbol.charAt(0)){
case '*': result = op1 * op2;
break;
case '+': result = op1 + op2;
break;
case '-': result = op1 - op2;
break;
case '/': result = op1 / op2;
break;
case '%': result = op1 % op2;
break;
Integer isOperand = new Integer(result);
operands.push( isOperand );
value = ((Integer)operands.pop()).intValue();
return value;
public static void main(String args[]) throws IOException {
JOptionPane.showMessageDialog(null, "Hello user! I hope you have a wonderful time using the
calculator. = ]" , "Welcome", JOptionPane.PLAIN_MESSAGE);
JOptionPane.showMessageDialog(null, "Note: Enter Infix expressions with spaces in between.",
"Welcome", JOptionPane.PLAIN_MESSAGE);
String infix = JOptionPane.showInputDialog("Enter Mathematical Expression Here: ");
String output = "The expression in Postfix is: " + convertToPostfix(infix);
JOptionPane.showMessageDialog(null, output);
String answer = "The answer to the equation: " + evaluate(convertToPostfix(infix));
JOptionPane.showMessageDialog(null, answer);
String options[] = {"Yes","No",}
int option = JOptionPane.showOptionDialog(null,"Do you want evaluate an expression?", "Calculator",
JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE, null,options,options[0]);
JOptionPane.showMessageDialog(null, "Thank you for using the calculator.\n Have a nice day! = ]");
}Can probably be done better...
boolean stop = false;
while(!stop) {
//your optionpanes..
if(option == 0) {
stop = true;
}Also, your yes/no optionpane could be exchanged to:
int option = JOptionPane.showConfirmDialog(null,"Do you want evaluate an expression?", "Calculator", JOptionPane.YES_NO_OPTION);Edited by: prigas on Sep 20, 2008 12:04 PM -
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Hey there.
I'm fairly new to java so bear with me here.
I'm having trouble with a program that, in short, reads from a file.
Let me shorten a show the code to you...
//main opens up and in a bit we get to...
if (loginVerify())
//and the if continues.
fileIn.close();
//main ends
public boolean loginVerify() throws IOException
openIn(); //Checks for validity - It's a long story why I //didn't just put the code in loginVerify(). I //don't think it should matter.
String str = verifyLog(); //Does the actual reading
str = str.substring(1);
if (str == placeHold) //Don't worry about not making placeHold,
//I made it global for testing reasons.
return true;
else
return false;
private String verifyLog() throws IOException
String str;
while (true)
str = fileIn.readLine();
if (str == null)
break;
else if (str.charAt(0) == 1)
return str;
//ADDITION OF OTHER NUMBERS
else
return str = "invalid";
private void readIn() throws IOException
BufferedReader console =
new BufferedReader(new InputStreamReader(System.in));
openInputFile(fileName);
if (fileIn == null)
System.out.println("*** Can't open " + fileName + " ***");
return;
private static void openInputFile(String fileName)
try
fileIn = new BufferedReader(new FileReader(fileName));
catch (FileNotFoundException e)
So it's fairly simple. It checks for validity and then reads lines until it finds one with the first char as '1' when it finds it, it reads the rest of the line off.
The error I'm getting is as follows: Exception java.io.IOException must be caught, or it must be declared in the throws clause of this method.
I've added throws IOException to them in attempts to fix the error but to no avail. I've tryed putting the catch in different spots... again, doesn't work.
I'm using codewarrior IDE version 5. I'm fairly sure it's the newest. I installed Java SDK 1.3 with codewarrior originally but I installed 1.4.1 recently.
If you need to see anything else about it, please tell me. I'd be more than happy to post a little more if it'll help.
ThanksOk. I worked through a bunch of throws and now I've found one I can't seem to conquer.
private String verifyLog()
String str = "";
while (true)
try {
str = fileIn.readLine();
catch (FileNotFoundException g) {
if (str == null)
break;
else if (str.charAt(0) == 1)
return str;
//ADDITION OF OTHER PEOPLE
else
return str = "invalid";
return str = "invalid";
}This time the error is at the reference to readLine() and it tells me the same error as before. I have a catch set up there, don't I?
readLine() is something I didn't create so I don't know how I'd tell it to throw an exception if I had to...
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Resetting your settings
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http://www.apple.com/contact/ -
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order entity -
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@Id
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//getters and setters...
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long orderId=order.getOrderId(); //get order id after persisting
for(SCItem item : listOfItems) //save details of order
DetailsOfOrders detail=new DetailsOfOrders(orderId,"1");
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thanks in advanced.yes, the entity classes have no-arg constructors (i just tried to write it shortly here...)
about the other thing , well i'm sorry , the right code is-
session bean (order method) -
List<SCItem> listOfItems; //SCItem is a regular class
Orders order=new Orders(userName);
manager.persist(order);
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for(SCItem item : listOfItems) //save details of order
DetailsOfOrders detail=new DetailsOfOrders(orderId,item.getProductId());
manager.persist(detail); //exception occures here
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