I have been working on an assignment for my class in programming. I am working with NetBeans. I finished my project and it worked fine. I am getting a message that says "No main class found" when I try to run it. Here is some of the code with the main:
package luisrp3;
import java.io.FileNotFoundException;
import java.io.PrintStream;
public class LuisRp3 {
public static void main(String[] args) throws FileNotFoundException {
java.io.File newFile = new java.io.File("LuisRamosp4.txt");
if (newFile.exists()) {
newFile.delete();
}
System.setOut(new PrintStream(newFile));
Guitar guitar = new Guitar();
I posted this before but had a couple issues. i have fixed the others and now have just this one remaining. Any advice will be greatly appreciated.
Right click on your Project in the project explorer
Click on properties
Click on Run
Make sure your Main Class is the one you want to be the entry point. (Make sure to use the fully qualified name i.e. mypackage.MyClass)
Click OK.
Run Project :)
If you just want to run the file, right click on the class from the package explorer, and click Run File, or (Alt + R, F), or (Shift + F6)
Also, for others out there with a slightly different problem where Netbeans will not find the class when you want when doing a browse from "main classes dialog window".
It could be that your main method does have the proper signature. In my case I forgot the args.
example:
public static void main(String[] args)
The modifiers public and static can be written in either order (public static or static public), but the convention is to use public static as shown above.
Args: You can name the argument anything you want, but most programmers choose "args" or "argv".
Read more here:
http://docs.oracle.com/javase/tutorial/getStarted/application/
When creating a new project - Maven - Java application in Netbeans
the IDE is not recognizing the Main class on 1st class entry. (in Step 8 below we see no classes).
When first a generic class is created and then the Main class is created Netbeans is registering the Main class and the app could be run and debugged.
Steps that worked for me:
Create new project - Maven - Java application
(project created: mytest; package created: com.me.test)
Right-click package: com.me.test
New > Java Class > Named it 'Whatever' you want
Right-click package: com.me.test
New > Java Main Class > named it: 'Main' (must be 'Main')
Right click on Project mytest
Click on Properties
Click on Run > next to 'Main Class' text box: > Browse
You should see: com.me.test.Main
Select it and click "Select Main Class"
Hope this works for others as well.
The connections I made in preparing this for posting really cleared it up for me, once and for all. It's not completely obvious what goes in the Main Class: box until you see the connections. (Note that the class containing the main method need not necessarily be named Main but the main method can have no other name.)
I had the same problem in Eclipse, so maybe what I did to resolve it can help you.
In the project properties I had to set the launch configurations to the file that contains the main-method (I don't know why it wasn't set to the right file automatically).
In project properties, under the run tab, specify your main class.
Moreover, To avoid this issue, you need to check "Create main class" during creating new project. Specifying main class in properties should always work, but if in some rare case it doesn't work, then the issue could be resolved by re-creating the project and not forgetting to check "Create main class" if it is unchecked.
If the advice to add the closing braces work, I suggest adding indentation to your code so every closing brace is on a spaced separately, i.e.:
public class LuisRp3 {
public static void main(String[] args) throws FileNotFoundException {
// stuff
}
}
This just helps with readability.
If, on the other hand, you just forgot to copy the closing braces in your code, or the above suggestion doesn't work: open up the configuration and see if you can manually set the main class. I'm afraid I haven't used NetBeans much, so I can't help you with where that option is. My best guess is under "Run Configuration", or something like that.
Edit: See peeskillet's answer if adding closing braces doesn't work.
There could be a couple of things going wrong in this situation (assuming that you had code after your example and didn't just leave your code unbracketed).
First off, if you are running your entire project and not just the current file, make sure your project is the main project and the main class of the project is set to the correct file.
Otherwise, I have seen classmates with their code being fine but they still had this same problem. Sometimes, in Netbeans, a simple fix is to:
Copy your current code (or back it up in a different location)
Delete your current file
Create a new main class in your project (you can name it the old one)
Paste your code back in
If this doesn't work then try to clear the Netbeans cache, and if all else fails, then just do a clean un-installation and re-installation of Netbeans.
In the toolbar search for press the arrow and select Customize...
It will open project properties.In the categories select RUN.
Look for Main Class.
Clear all the Main Class character and type your class name.
Click on OK.
And run again.
The problem is solved.
If that is all your code, you forgot to close the main method.
Everything else looks good to me.
public class LuisRp3 {
public static void main(String[] args) throws FileNotFoundException {
java.io.File newFile = new java.io.File("LuisRamosp4.txt");
if (newFile.exists()) {
newFile.delete();
}
System.setOut(new PrintStream(newFile));
Guitar guitar = new Guitar();
}}
Try that.
You need to add }} to the end of your code.
You need to rename your main class to Main, it cannot be anything else.
It does not matter how many files as packages and classes you create, you must name your main class Main.
That's all.
import java.util.Scanner;
public class FarenheitToCelsius{
public static void main(String[]args){
Scanner input= new Scanner(System.in);
System.out.println("Enter Degree in Farenheit:");
double Farenheit=input.nextDouble();
//convert farenheit to celsius
double celsuis=(5.0/9)*(farenheit 32);
system.out.println("Farenheit"+farenheit+"is"+celsius+"in celsius")
{
I also experienced Netbeans complaining to me about "No main classes found". The issue was on a project I knew worked in the past, but failed when I tried it on another pc.
My specific failure reasons probably differ from the OP, but I'll still share what I learnt on the debugging journey, in-case these insights help anybody figure out their own unique issues relating to this topic.
What I learnt is that upon starting NetBeans, it should perform a step called "Scanning projects..."
Prior to this phase, you should notice that any .java file you have with a main() method within it will show up in the 'Projects' pane with its icon looking like this (no arrow):
After this scanning phase finishes, if a main() method was discovered within the file, that file's icon will change to this (with arrow):
So on my system, it appeared this "Scanning projects..." step was failing, and instead would be stuck on an "Opening Projects" step.
I also noticed a little red icon in the bottom-right corner which hinted at the issue ailing me:
Unexpected Exception
java.lang.ExceptionInInitializerError
Clicking on that link showed me more details of the error:
java.security.NoSuchAlgorithmException: MD5 MessageDigest not available
at sun.security.jca.GetInstance.getInstance(GetInstance.java:159)
at java.security.Security.getImpl(Security.java:695)
at java.security.MessageDigest.getInstance(MessageDigest.java:167)
at org.apache.lucene.store.FSDirectory.<clinit>(FSDirectory.java:113)
Caused: java.lang.RuntimeException
at org.apache.lucene.store.FSDirectory.<clinit>(FSDirectory.java:115)
Caused: java.lang.ExceptionInInitializerError
at org.netbeans.modules.parsing.lucene.LuceneIndex$DirCache.createFSDirectory(LuceneIndex.java:839)
That mention of "java.security" reminded me that I had fiddled with this machine's "java.security" file (to be specific, I was performing Salvador Valencia's steps from this thread, but did it incorrectly and broke "java.security" in the process :))
Once I repaired the damage I caused to my "java.security" file, NetBeans' "Scanning projects..." step started to work again, the little green arrows appeared on my files once more and I no longer got that "No main classes found" issue.
Had the same problem after opening a project that I had downloaded in NetBeans.
What worked for me is to right-click on the project in the Projects pane, then selecting Clean and Build from the drop-down menu.
After doing that I ran the project and it worked.
Make sure the access modifier is public and not private. I keep having this problem and always that's my issue.
public static void main(String[] args)
I'm working on a JavaFX project in Netbeans that's currently around 3000 lines long, and I've packaged as an .exe regularly for testing but never come across an issue like this curious incident.
When packaging natively as a Windows .exe file, I found that after installing the .exe and launching my program I was getting a popup saying "Class {mypackage}/{mymainclass} not found." followed by "Failed to launch JVM."
Launching the program in Netbeans, packaging as an .exe, and launching the .jar in Powershell with "java -jar {app}.jar" all gave absolutely no errors. Even the .jar inside the installed application folder was fine, with no errors on the command line.
After a few hours of trawling through git commits and packaging natively, I managed to trace the issue down to a single line of code:
private static ComboBox choices = new ComboBox();
When I initialise the ComboBox in an initialiser, the program magically works after being installed from an .exe:
private static ComboBox choices;
{
choices = new ComboBox();
}
However, when I use a static initialiser (by placing static in front of the first curly brace), even though Netbeans states "initialiser can be static", I get the same error as before.
This is puzzling, because Java is obviously fine with the code itself, but after it's been through the native packager it will not launch. I've used plenty of similar lines of code to initialise static variables in other classes, with no ill effects.
I tried adding a similar line to the main class: private static CheckBox chkbox = new CheckBox();
It caused the exact same error after the .exe was installed (as before, the .jar was fine), but when I cut-and-pasted the line to a different class, it had no effect.
Interestingly, my main class already has a static boolean that is initialised in the same way that the ComboBox and CheckBox were: private static boolean someBool = true; but the boolean causes no problems.
Can anyone explain the reason behind this? Thank you.
Edit: I also tried packaging on a different machine, but it stopped working after the same git commit.
I'm using version 1.8.0_144 of the JDK and JRE.
Edit 2: here is the main class of a simple example that produces the error.
package testproject;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.CheckBox;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
public class MainApplication extends Application {
private static CheckBox testCheckBox = new CheckBox(); // Causes error after launching from installed .exe
/* UNCOMMENT THIS SECTION AND REMOVE THE " = new CheckBox()" ABOVE TO FIX THE ERROR
{
testCheckBox = new CheckBox();
}
*/
#Override
public void start(Stage primaryStage) {
StackPane root = new StackPane();
Scene scene = new Scene(root, 300, 250);
primaryStage.setTitle("Empty window");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
I would avoid creating JavaFX widgets in static initializers (such as a static field or static block), as this would create them when class is loaded, which might happen in any thread. You want that to happen in JavaFX Application Thread.
In your case it happens in main thread, which is definitely not correct.
Check this answer for more details about JavaFX application startup, and how threads are involved in the process.
Trying to initialize a JavaFX widget outside of "JavaFX Application Thread" is (to my understanding) undefined behavior, and might fail in many different ways (or succeed by luck). If that creation fails, then the class loading fails (because static init has failed), hence "class not found". Unfortunately, since this happens while loading main class, you don't get to see the initial error, just "class XXX not found".
Possibly in your case, the java launcher can deal with this initialization just fine, but the launcher used by your .exe is different. I'm not too surprised it fails. I'm equally surprised it works with regular java :)
When I input the following Java code into eclipse, it returns an error. I am told by the eclipse tutorials that this should work. What am I doing wrong?
This is a picture of my code.
import org.eclipse.swt;
public class SWTHELLOWORLD{
public static void main(String[] args){
Display display=new Display();
Shell shell = new Shell(display);
shell.setText("Hello world");
shell.open();
while(!shell.isDisposed()){
if(!display.readAndDispatch())display.sleep();
}
display.dispose();
}
}
When I run as a java application, it returns this error:
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
Display cannot be resolved to a type
Display cannot be resolved to a type
Shell cannot be resolved to a type
Shell cannot be resolved to a type
You are not importing the Display and Shell classes.
You should add the following imports to the top of your class:
import org.eclipse.swt.widgets.Display
import org.eclipse.swt.widgets.Shell
Just importing org.eclipse.swt will not import all the classes that you need.
You used
public static void main (Strings[] args)
while the correct way of putting it would be
public static void main (String [] args)
Mind that it is String without the 's' in the end.
When I run the below code, I get the error that Could not find or load main class. I have removed the package and created it again. But the error is still exist. I did some methods to fix it such as right clicking on package name -> properties -> run option to change the main method but there is nothing. But if I create another package name and write this code in it, the program work.
package craps;
public class Craps {
public static void main(String[] args) {
int number = 10;
System.out.println(number);
}
}
Your code is not having any errors
I don't know what is happening in Netbeans .I have been using this for years and living with this kind of errors.
perhaps you get this when netbeans running out of memory and that particular moment you are editing this file.
My workaround for this kind of errors are
1.Do some dummy editing in that file like commenting some empty line // and save All and recompile it
2.Close and open this project (Sometimes work)
I am currently in a Java class using Java: How to Program, Ninth Edition
I am following the book in creating a GradeBook and have come across an error stating no main classes found.
Here is the code for the two files in my project folder:
GradeBook.java
// Fig. 2.1: GradeBook.java
// Class declaration with one method.
public class GradeBook
{
// display a welcome message to the GradeBook user
public void displayMessage()
{
System.out.println ( "Welcome to the Grade Book!");
} // end method displayMessage
} // end class GradeBook
GradeBookTest.java
// Fig. 3.2: GradeBookTest.java
// Creating a GradeBook object and calling its displayMessage method.
public class GradeBookTest
{
// main method begins program execution
public static void main( String[] args )
{
// create a GradeBook object and assign it to myGradeBook
GradeBook myGradeBook = new GradeBook();
// call myGradeBook's displayMessage method
myGradeBook.displayMessage();
} // end main
} // end class GradeBookTest
I am using the NetBeans IDE to create and run my projects. It is only my second week into my Java class so I am still learning and working my way around NetBeans and Java. Any advice would be awesome.
If it was eclipse, I would have just run the main method in the GradeBookTest. Are you trying to run the project ? or just the GradeBookTest main ?
Try running GradeBookTest.
In the project properties, under "Run" pick GradeBookTest as the class to run.
Try selecting the file and pressing Ctrl+Shift+F10. If this doesn't work, check if JAVA_HOME is set properly and that you are using the correct compiler (javac) under Settings->Compiler->Java Compiler. I dont have sufficient points to post a screenshot, otherwise I have the exact thing running on my machine and I could have shared the screenshot.
There are reasons and ways to solve this problem
the class is not located in the proper src directory of your project.
Secondly if you have created classes you have to compile them before they can be used as main.
Right click on the file name on the Tree menu on left and select compile. Otherwise the short cut key to compile class is F9 .
This will definitely solve your problem :) .