I want to create a simple java class, with a main method, but when I compile my code, I get this error message :
Error: Main method not found in class errors.TestErrors, please define
the main method as: public static void main(String[] args)
This is the source code :
package errors;
public class TestErrors {
public static void main(String[] args){
System.out.println("hello");
}
}
Why I'm seeing this error, as you can notice I've alreader declared the main method !
As said in my comments, looks like you've declared a String class among your own classes. To prove this, I've created a basic example:
class String {
}
public class CarelessMain {
public static void main(String[] args) {
System.out.println("won't get printed");
}
public static void main(java.lang.String[] args) {
System.out.println("worked");
}
}
If you execute this code, it will print "worked" in the console. If you comment the second main method, the application will throw an error with this message (similar for your environment):
Error: Main method not found in class edu.home.poc.component.CarelessMain, please define the main method as:
public static void main(String[] args)
This usually happens if ur complete project isnotconfigured correctly
or one of your class in project has still some errors
in such cases IDE will prompt stating the same that project contains some error
and you still proceed (ie run your class)
as project has some bugs new classes will not be created and IDE will run
the class which was available previously
to make sure this is ur case u can add new class in your project and try to run it and if ur getting no such class exist then there its is a perfect evidence
Just check your java file, it has not been saved. Please save all java files before compiling.
If the answers above are not working for you: make sure "main" is not capitalized in your method definition.
OK:
public static void main(String[] args)
ERROR:
public static void Main(String[] args)
Though the error message makes the required syntax for the main method clear, incorrect caps can be hard to spot. It took me ~30 minutes of troubleshooting to find this typo today. This was clearly not an issue for the OP, but is another easy/likely way to produce the same error message, and this answer may help other users.
I had this issue just now. This error came up because the JRE file that i switched out didn't had the full library. After I corrected/added the right JRE system library the problem went away.
Right click on the class name (which you are trying to run)->Run As->Run Configurations->Under Main Class Tab
Write your main class name and hit on Run.
Try commenting the first line.
//package errors;
Related
package concurrencyTest;
public class concurrencyTest implements Runnable
{
#Override
public void run()
{ System.out.println("Hello from a thread!"); }
public static void main(String[] args)
{
concurrencyTest c = new concurrencyTest();
Thread t = new Thread(c);
t.start();
}
}
Hi, I'm just trying to get my java concurrency test to run. But I'm getting this error :
Error: Main method not found in class concurrencytest.ConcurrencyTest, please
define the main method as:
public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application
I'm guessing that somewhere, in the myriad of project directories and subfiles that a java program needs to run, the name of the project or class has been wrongly referenced in lowercase letters. I've manually been thru all the files I can find that span from the root directory and renamed any instance of lowercase 'concurrencytest'. But still it seems the compiler finds a reference to lowercase concurrencytest and so refuses to compile. Any idea where this reference may be?
My root directory, source directory, and java code file are all called 'concurrencyTest'
edit
amended the original code for this question to include 'static' in the main method definition. Doing this was necessary but has not fixed the problem.
You wrote the main definition wrong. You should change it as below:
public static void main(String[] args) {
// ...
}
I found a reference to 'concurrencytest' in the meta file ...\concurrencyTest\nbproject\project.properties
So I changed it to 'concurrencyTest'
Also when NetBeans can't find the expected main method in the class it expects, it opens a 'RunProject' window where it lists main methods from classes it has found. For me it found a main in 'concurrencyTest' so I selected it.
One of these actions solved the problem, but not sure which one.
Take this code for instance
public class Hello
{
static void main(String[] args)
{
System.out.println("Hello World");
}
}
Here, I didn't write public for the main method and compiled the class. When I run the program why does the error read as "Could not find or load main class Hello.java".
My question is, if main(String[] args) is a 'method' then why say 'main class'?The point is not that public is there or not. The point is that I changed access modifier which caused main(string[] args) to be invisible to JVM. So why does JVM say main class and not main() method?
P.S. If this a stupid question then I really regret asking it.
Edit:-
Here is the error message
Error: Could not find or load main class Hello.java
There are two problems here.
main() must be declared as public static void.
However the real problem was your command line. Clearly it was
java Hello.java
It should have been
java Hello
There is no such class here as Hello.java. The name of the class is Hello.
Can't seem to figure out why this simple program has stopped working on my computer. My programs that I compiled up until a Windows update are fine but when I try to compile a new program I get the following. I've attached a picture of the program and the command prompt error message. I've checked the CLASSPATH and it looks fine.
Program - HelloWorldApp.java
class HelloWorldApp{
public static void main(String[] args){
System.out.println("Hello World!"); //Display the string
}
}
execute javac HelloWorldApp.java - all is fine
execute java HelloWorldApp -
Error: Main method not found in class HelloWorldApp, please define
the main method as: public static void main(String[] args) or a JavaFX
application class must extend javafx.application.Application
Please excuse me if this has been answered. I searched but couldn't find this problem
Have you declared a String class among your list of classes? If so, try using java.lang.String[] args as argument to your main method.
class a {
public static void main(String args[]) {
}
}
i want to print "hello world" without touch or use above code and also without use of static and final keyword......
What are the different ways to initiate code execution.
Use public static void main(String args[]) { ... }
Use your static class initializer static { ... }. Problem: You need to get the class to load first. Solution: attempt to start the main method, but that means you need to have at least an empty main. However - OP states we cannot use 'static'.
Use an instance initializer { ... }. Problem: How do you instantiate an instance. Solution: initialize a static field with a class instance. However - OP states we cannot use static fields.
So what is left. I assume that we can use the empty main posted by the OP. From there on we build up a 4th solution:
public enum Play {
PLAY;
{ System.out.println("Hello World!"); }
public static void main(String args[]) { }
}
This should fulfill the conditions:
we do not modify the static main method, although we need the empty body just to get the class loaded.
we do not use a static initializer, we use an instance initializer instead.
to instantiate, and get the instance initializer started, we use an enum. Enum's start the initializer for each instance, meaning for each of the enum constants.
Also note the output when you try to execute a class without a main:
$ java -classpath . Play
Error: Main method not found in class Play, please define the main method as:
public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application
So that leaves us also the clue that we potentially can use javafx.application.Application. I did not investigate this trail any further.
You can create a JavaFX application, which is usually for displaying a GUI, and use it to output hello, world to the console and immediately shut the JavaFX GUI system down. JavaFX applications are executed by a special launch path in the java launcher. JavaFX applications do not need a main, static and final keywords.
The following snippet is just for demo purposes, I wouldn't recommend writing a JavaFX application unless you actually wish to display a GUI.
import javafx.application.Application;
import javafx.application.Platform;
import javafx.stage.Stage;
public class PlayApp extends Application {
#Override
public void start(Stage stage) {
System.out.println("hello, world");
Platform.exit();
}
}
// Totally useless code from the original question
// goes below the real app code and is just ignored
// and never used when the application runs.
class a {
public static void main(String args[]) {
}
}
You need to use Oracle Java 8+ to compile and execute the JavaFX application as below:
javac PlayApp.java
java PlayApp
The a class is in the PlayApp.java file only to meet the original poster's requirement from a comment:
it means the above code is fixed, you can't modify the above code but yes u can write anything to print "hello world" above or belove this code
Really, if you are writing a console application, just use a standard app format (with a static main method) instead:
class HelloWorldApp {
public static void main(String[] args) {
System.out.println("Hello World!"); // Display the string.
}
}
Unrelated advice on asking questions
In future, if you post such questions, I suggest that you also supply the reason for the question and why the bizarre constraints are placed on solutions. Also, address concerns such as WorldEnder's first comment on your question: "is this a code challenge? If not.. why?"
You can't just print "hello world" without MAIN method and also without using STATIC and FINAL key word in java because the main method is a function required you don't have to apply any rocket science in that thing if u are using intelliJ IDEA or any other IDE anyways this is the code
public class Basics_Of_Java {
public static void main(String[] args) {
System.out.println("Hello world");
basics of java in 1st line is the name of the java file you may have another name.
When I create a new main.java file in the default package in my Eclipse project, it generates a main method that looks like:
public static void main(String[] args)
{
}
This immediately raises a warning that says This method has a constructor name. The suggested fix is to remove the void:
public static main(String[] args)
{
}
Now rather than a warning, I get an error: Illegal modifier for the constructor in type main; only public, protected & private are permitted. If I remove the static, my code now looks like:
public main(String[] args)
{
}
This time, I still get an error, but a different one that says:
Error: Main method not found in class main, please define the main method as:
public static void main(String[] args)
Argggh! But that takes me right back to where I started. How do I define the main method so that I don't get any errors or warnings?
I'm using Eclipse Juno Service Release 2 and JavaSE-1.7. Please note, I'm very new to Java; I come from a C# background. Also, this is probably a duplicate question, but I can't find it.
Don't call your class main, but Main.
In general, stick to the Java coding standards: start class names with a capital (Main instead of main) and you won't run into these problems.
If you name the file main.java the class has to be named main too, which is against standard (classes start with a capital letter) but possible. In a class a method named the same as the class is considered a constructor. So to fix your problem and fit the standard rename your class and the file to Main with a capital "M"
Change the name of your class from main to Main or to something else. Also, following the JavaBean API specification, your classes must be in CamelCase with the first letter in capital.
Not 100% related with question, but you should also do not create classes with the names of Java JDK classes, for example String:
public class String {
public static void main(String[] args) {
System.out.println("Try to execute this program!");
}
}
This won't only give problems to compiler/JVM but also for future readers (remember that you are a future reader of your own code as well).
Note: to fix the code above, just refer to java.lang.String class using its full name:
public class String {
public static void main(java.lang.String[] args) {
System.out.println("Try to execute this program!");
}
}
Or even better, change the name of the class.
In java, the class name and file name must match. If you have a file named main.java, then the class name has to be Main too, and in that case, the constructor method would be named main, so you couldn't have a main method.
Change your file and class name to something other than main.