I currently don't have a working way to edit and run Java on my computer, so I'm trying to get Atom working with Java (I realize it's not a Java IDE and I'm not trying to make it one, I just want to be able to do some light Java work on my laptop). I've installed the script and instant-build packages for Atom and wrote the following test code in a file called "main.java' in my project folder:
class Main{
public static void main(String[] args) {
System.out.println("please");
}
}
When I try to run the code with cmd+i (I'm on a 2012 MacBook Pro) and get the following error message:Error: Could not find or load main class main.
I'd be happy to provide any further information; thanks for helping!
The huge problem of learning Java is that you need to launch the projects in a very strict way, and setting the classpath is always problematic. The solution lays in the following (pretty enigmatic) line of the "Script" documentation:
Project directory should be the source directory; subfolders imply packaging.
So, instead of opening a plain file, open the project (folder) with .java classes or define inside the file, the package to which your .java belong.
It's due to the fact that JDE needs to create a virtual target in form of .classess and single .java file definitely can't be launched as standalone file. I suppose that "Script" is not able to locate the source folder when you try to execute seperate .java file.
Before launching your .java files always "Add Project Folder..."
Please remember that it's not possible to have several folders opened if they don't belong to the same project. Such situation cause problems of locating the right classpath and in the end javac prompts the error.
You have to name your file with the first letter in upper case Main.java, since it must match the name of your class
I replicated the issue quite easily. If I created a new directory in Atom itself and then tried to run the code it didn't work as your error message came up for me as well. Error: Could not find or load main class main.
I used an existing directory and then created a file inside that folder in Atom and ran the same code it worked. I then copied and pasted that same file into the directory of my choice and it worked.
Related
I want to use my "Final_Frame.java" in my "SampleFrameProject.java", sort of like interconnecting it by creating a "Final_Frame" object and then typing the "this.show()".
However, an error message appears, saying that "package com.toedter.components does not exist." That is the only error I've seen; I'm confident that my "Final Frame.java" is functioning well before I copy-paste it, hence I knew the issue was caused by my copy-pasting.
Btw all of the error is pointing to JCalender, and JComponents, I'm pretty sure I followed the instructions while installing them. They are working just fine before I move the "Final_Frame.java", but after I move it, it began to show errors. So is there any way for me to copy-paste it correctly? or are there any methods to call "Final_Frame.java" inside my "SampleFrameProject.java" without copy-pasting?
Thank you in advance!
package is a fundamental concept in Java. It is nothing but a namespace for the Java source file, reflecting the directory (folder) structure of your project after the src/main/java directory.
package is usually defined at the first line of the file. For example, given the directory structure from your root directory mavenproject2, the directory structure inside if it is src/main/java/com/foo/bar/FinalJava.java, then the corresponding package defined will be
package com.foo.bar;
// imports
public class FinalJava {
// the content of class
}
For your case, it would seem that you have copied com/toedter/components/FinalFrame.java from the Hotel_Management_System project (which already has defined a line package com.toedter.components in the file) to another project mavenproject2 which has a different directory structure (which is not clear in your question).
The solution would be to modify the package line according to your directory structure then it would solve the error.
Personally, I would suggest to learn some basics in Java, take some tutorials, or at least write some simple Java console applications before diving into GUI applications.
My code has gotten quite large and so I've decided to build a runnable JAR to see how it's done. I probably should've tried sooner because I'm getting 2 different errors related to the project structure, first is the "no main manifest attribute error" when trying to run the JAR from command prompt. Double-clicking the JAR does nothing (Win7). The second issue is related to the FXMLLoader explained lower down.
I followed the steps here to build the JAR, which involved moving all Maven files into the JAR directory. The compiled JAR gave me the manifest error, so I followed this which adds a Maven plugin in my pom.xml file. The error might be caused by a wrong naming convention with the line <mainClass>com.primary.Drag</mainClass> where primary is the package and Drag is my Drag.java file (class) which has the main method.
Inititally I was using the default package but read that this is not recommended for larger projects, so I put all my files into "primary". Here is my current hierarchy as shown in IntelliJ:
The problem is that ever since I created the "primary" package, I can no longer even compile the program via IntelliJ, let alone build a runnable JAR. This is due by the second error I mentioned, which is java.lang.IllegalStateException: Location is not set. on this line within primary/Drag.java:
FXMLLoader loader = new FXMLLoader(getClass().getClassLoader().getResource("firstlaunch.fxml")); It used to work with the default package, but not anymore.
I tried replacing firstlaunch.fxml with /primary/firstlaunch.fxml and /resources/firstlaunch.fxml (with and without moving resources into primary package) but no luck.
3 Related Questions:
Is my project structure incorrect?
How do I reference the fxml file from the primary package?
Is this what I should write in Maven's mainClass tags? <mainClass>com.primary.Drag</mainClass>
Is my project structure incorrect?
Answer:
Your package name should be like com.primary.******
How do I reference the fxml file from theprimary package?
Answer:
Always make sure that you are trying to load firstlaunch .xml from the class which is located in same package where that xml is kept. Means class which you wrote the loading code and xml file should be in same package
Is this what I should write in Maven's mainClass tags?com.primary.Drag
Answer:
If you package name corrected to com.primary , your main class Drag will correctly added by maven
So I'm completely new to programming, and I've been writing some Java with the NetBeans IDE. My code runs fine within NetBeans, but I've tried to run it using the command line as well. However, if I run it from the command line, I have to delete the line:
package firstprogram;
which NetBeans automatically places at the top of each new file, or I get the error:
Error: Could not find or load main class FirstProgram
However, if I do delete the line, then the program no longer runs within NetBeans! It doesn't seem right that I have to choose whether to run a .java from within NetBeans or without.
The research I've done makes me think that this is something to do with directory structure? But everything I read on that goes straight over my head. NetBeans has a structure with "build", "dist", "nbproject", and "src", but when I use the command line I just place the .java file in an empty directory and javac from there.
Any explanation is appreciated! The books and tutorials I'm learning from either assume you're just using NetBeans or don't have the package line at all.
You can compile your class using javac command from anywhere, as long as you provide correct relative or absolute path. The problems come when you want to run your program using the java program.
You have to provide the correct path corresponding to your package declaration. For example, if I had 'MyClass' in package mypackage, first line would look like this:
package mypackage;
class source stored on disk:
c:/MyNetbeansProject/src/mypackage/MyClass.java
Compiled bytecode:
c:/MyNetbeansProject/build/classes/mypackage/MyClass.class
Now, if I would have opened a command prompt/terminal in folder c:/MyNetbeansProject/build/classes/, I could run the program using java mypackage/MyClass or java mypackage.MyClass.
However, if i would be somewhere else, I would have to say where the class files are located using the cp option: java -cp c:/MyNetbeansProject/build/classes mypackage/MyClass. The path in cp option can be relative or absolute, use "" when it contains spaces.
Package are directory architecture.
If your class is in the package com.acme.test, the class should be in the com/acme/test directory.
Instead of placing your class in an empty folder, place it in a folder named firstprogram and do javac firstprogram/youclass.java
The package (and folder) permit you to arrange your architecture with logical pattern.
More info here : http://www.tutorialspoint.com/java/java_packages.htm
So like OcterA said, you should keep organized, but with only one class this is not the issue. I believe that your problem is that you are not entering the correct command into the command line.
First cd to the correct directory and when you want to execute a file within a package in that directory you need to enter
java packageName.className
In this case
java firstprogram.FirstProgram
I want to use clearNLP (http://clearnlp.wikispaces.com/) for extracting semantic role labels of an input sentence. I followed the instructions here: http://clearnlp.wikispaces.com/installation (I downloaded the jar files, put them in a directory called ClearNLP and set the classpath) but when I run the command java com.clearnlp.run.Version, I face the error: Could Not find or Load Main.
I tried it twice: Once I set the classpath as an environment variable of windows and ran the command in CMD. But, when it didn't work, I tried to create a java project, set the libraries using NetBeans and run the program. But, it didn't work, too.
BTW, when I run echo %classpath% command, I see that the classpath is set correctly.
Can anybody help me?
Try Eclipse. I included the jars in a new project I created. I then created a simple class like so
package test;
import com.clearnlp.run.Version;
public class TestClearNLP {
public static void main String(args[]) {
Version.main(args);
}
}
When run, this creates output in the console of:
ClearNLP version 2.0.2
Webpage: clearnlp.com
Owner : Jinho D. Choi
Contact: support#clearnlp.com
The only weird situation I ran into was that Eclipse did not like the jar files beginning with a period. I removed those from my project and ran with the remaining libraries.
I'll try to illustrate the problem as simple as I can.
I have a JAR file, which I extracted using Winrar. (The jar file contains an open source android library).
I want to modify this JAR file by adding a new class to the library.
So here are my steps:
First, I created a class using Eclipse and set the package name same as the android's library package name.
Second, I copied this java File to the folder of the other java files in the library.
Third, I tried to compile the JAVA file via the CMD using javac.
The path of the new java file and the other .JAVA and .CLASS files of the library is: C:\com\example\core\
The name of the new java file would be: "MyNewClass.java"
The command I run via the CMD is: javac C:\com\example\core\MyNewClass.java
But, during the compilation I get many errors saying: Cannot find symbols.
I've been looking up for a solution of this problem but couldn't figure how to solve it and make the new JAR File having another class that I created seperately.
What am I missing?
As per earlier comments:
Rather than trying to modify the JAR, you can get access to the full source code of the Universal Image Loader library by cloning the repository using git or hitting "Download ZIP" on the righthand side of the page you linked.
Once you have the source, import the library in your IDE. From there on you'll be able to build the whole thing from scratch, make any adjustments/modifications you like, etc.
Your classpath might be wrong or there might be some mistake in package name.
When a Java program is being compiled the compiler it creates a list of all the identifiers in use. If it can't find what an identifier refers to it cannot complete the compilation. This is what the cannot find symbol error message is saying, it doesn't have enough information to piece together what the Java code wants to execute.
Try:
javac -cp com/* C:\com\example\core\MyNewClass.java
That should make the compiler aware of all the other classes under com/...