I am trying to run my Example2.class program in windows 7 64-bit command prompt. I used command prompt already to compile the program, but when type: "java Example2" it gives me an error saying could not find or load main class example2. How do I set the right path to my file so that it can find it? Thanks
You need to give it the full package name, and (unless you change the class path) you need to be in the right directory. If the full package name is
com.something.Example2
then you'd expect the compiler to produce a file like this:
com/something/Example2.class
If you make sure you're in the directory immediately above com (i.e., you can see com when you do a directory listing), then you can run it with
java com.something.Example2
Note that it's case sensitive.
If you used the default package (i.e., the full class name really just is Example2) then you need to be in the directory containing Example2.class, and then you run
java Example2
But using the default package is discouraged.
The biggest thing you could do to help yourself out is to use an IDE (Eclipse or NetBeans are the most commonly used ones). As soon as you start to write anything at all large or complex, compiling and running from the command line without an IDE will cause you to claw your own eyes out.
When you write a class you can save the file as : MyClass.java and then execute this commands in this directory:
javac MyClass.java
which will compile the class and then create automatically the file: MyClass.class (If compilation ended without errors)
and then to run this SPECIFIC class execute the command:
java Myclass
Related
I'm having a problem where the java command - no matter what I'm trying to run, says that it Could not find or load main class.
Everything is fine when compiling with javac, .class files are created. So when I run:
javac HelloWorld.java
on
public class HelloWorld{
public static void main(String[] args){
System.out.println("Hello World");
}
}
everything compiles fine, a HelloWorld.class file is created along side the HelloWorld.java file. However when I then go to run:
java HelloWorld
1) the most telling sign is that when I press Tab to autofill HelloWorld nothing comes up.
2) when I do run it, I get the Error: Could not find or load main class HelloWorld despite it being in the same directory, not being part of a package, compiling fine with a .class file, the program having a main class.
For reference running Fedora 23 64bit, openjdk version "1.8.0_111".
Just a small reminder for the newbies in Java:
When compiling, you type:
javac MyClass.java
Now, you've got two files:
MyClass.class MyClass.java
Now, whereas you typed the .java extension when compiling, you must NOT type the extension .class when running the program. You should just type:
java MyClass
If you type java MyClass.class then you'll get:
Error: Could not find or load main class
Try using java -cp . HelloWorld
Some good reading: http://www.sergiy.ca/how-to-compile-and-launch-java-code-from-command-line/
You need to specify classpath parameter while running your example:
java -cp . HelloWorld
java -cp HelloWorld
works. I use windows 10, and was checking out the very course. I first had to add it to path, and spent time wasted on it. Be sure, however, to NOT include the .class part of the name. Java is not my first language, but Java is portable and is a suitable language for everyone.
The same happened to me while compiling a piece of code (that was initially writen for an IDE with several files) throug terminal. The problem was mentioning the package with the same name of the main class (package HelloWorld). I fixed it and now it works. Not sure if that's your case
May be you have removed your JDK From System.
You can change it using following steps
1> Select Project
2> Right Click On Project
3> Click On Properties
4> Go to Java Build Path
5> Click On Libraries Option
6> Select JRE System Library
7> Click On Edit
8> Change Your Library Accordingly
Trying to compile and run my java program from the commandline that is set up a bit weird. The file structure is as follows:
[ROOT]/
|
|____libs/
| |____myExtraJar.jar
|
|____src/
|____main/
|____com/
|____example/
|____myClass.java
The package is defined at the top of the java file as
package com.example;
I am able to compile the program fine (I think) while in the root folder, using
javac -classpath "/libs/myExtraJar.jar" src/main/com/example/*.java
I don't get any compilation errors (such the ones that occur if I leave off the classpath) and I can see that .class files are being created in the com/example/ folder. However, I can't find any way to run the compiled program. Running
java src/main/com/example/myClass
results in the message
Error: Could not find or load main class src.main.com.example.myClass
Any help would be appreciated.
You need to specify the classpath when you run it, and you also need to use the fully-qualified classname. Like,
java -cp "libs/myExtraJar.jar:src/main" com.example.myClass
Elliot is right. More precisely, you need to add the build directory to your classpath. It is the directory containing your *.class files, and is sometimes named target/.
$ java -cp "target:lib/myExtraJar.jar" com.example.myClass
Moreover, src/main/com/example/myClass should be com.example.myClass, which is the fully-qualified class name. See http://www.manpagez.com/man/1/java/ for details of the java command.
I am trying to run a java program through the Terminal on Mac, yet getting:
Error: Could not find or load main class (MY CLASSNAME)
I compiled this application with Eclipse, and when I run this with Eclipse, it works fine.
Furthermore, I am in the right directory, as when I type "ls" in the Terminal, it lists all the files, includes the class file I am trying to run.
This is what I type:
java mainClass
I would very much appreciate help to solve this!
Thank you,
Dean
EDIT: Solution - instead of java mainClass, it must have package too: java startPackage.mainClass
Start by making sure you are at the directory above the top level package
If the class belongs to the package com.foo.bar, you want to be in the directory above com.
In your case, you want to be in the directory above startPack.
Then you need to use the fully qualified name to run the class...
java statPack.mainClass
For example...
Make sure you have the current directory inside your CLASSPATH.
java -cp . mainClass
To set this globally, you can use export CLASSPATH=$CLASSPATH:. inside .bash_profile.
Separately, if your class lives inside a package such as com.foo.bar, then you will need to go to the parent directory of com and run your application with the full path.
java com.foo.bar.mainClass
I too faced this on Mac machine and then what I had to do to make it work was:
Problem Statement:
I had one package xyz under the root of project i.e src/main/java and then inside xyz package I had one class Student.java
my current directory is /Users/username/projectname/src/main/java/xyz:
I can see Student.java exists here
and I compiled it using javac Student.java
Now I see class file has been created at this location. But when I try to run the class file using java Student
I get the error: Error: Could not find or load main class Student
Solution:
Now the solution is to go one step back in the directory and go to root path:/Users/username/projectname/src/main/java and run the command
java xyz.Student
and it will work.
Link to follow: https://javarevisited.blogspot.com/2015/04/error-could-not-find-or-load-main-class-helloworld-java.html
For people dumb like me, make sure you are typing java HelloWorld - and NOT java HelloWorld.class - to run the compiled file with the name HelloWorld.class. This is especially so if you are used to hitting the tab key to complete the file name, as the terminal will give you java HelloWorld.class if you hit the tab key for autocomplete after typing something like java He...
This answer is here because it took 3 sites, including this answer, and 25 mintues before I figured out what I was doing wrong.
Logic is easy, typing is hard.
Using the absolute path can also resolve this problem:
java -classpath /Users/xingliu/IdeaProjects/springproject/src/main/java/ startPackage.mainClass
I understand there are a lot of threads similar to this one, but I couldn't find the one that solved my problem. Following this instruction I was able to get java in terminal and be able to compile. I am able to "javac main.java" with no errors, but when I "java main.java", it simply says it could not find or load main class main.java. I believe that my classpath is wrong but i'm not entirely sure how to fix this either. This is what comes out when I type in echo $PATH
/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/home/taka/.rvm/bin
and when I type echo $CLASSPATH it doesn't show anything.
I have also tried java -cp ./ main.java as that seemed to have worked when I compiled and ran HelloWorld.java
If your javac is successful then update your classpath environment variable and add current directory i.e. . in the classpath, then run the java as below:
java main
Please note: There is no .java extension as you need to run .class file(which was generated after javac) that also without mentioning the extension. Java uses generated class files to execute not the original source files.
main.java java is your source code . you cant run java source without compile. For compilation you should use javac command. After that it will create a main.class file which can understand by interpreter which is java.
So you to run your class use java main or java main.class
With reference to this post
Receiving "wrong name" NoClassDefFoundError when executing a Java program from the command-line
I did not understand how to solve the problem
Actually in my java source code there' s line :
package es_2011;
when I compile the program through JCreator everything works perfectly.
It creates a folder named es_2011 where to put .class files.
Also the executing operation goes smoothly, the program runs ok.
Now I'd like to use the command line only.
So I placed my java file in the directory where javac.exe is but whenever I try to compile I get the same error
The command I use is: javac ProgAudioJ.java
The path (where javac.exe is ) is : C:\Program files\Java\jdk1.6.0_22\bin
Is someone willing to help me understand in terms of exactly tell me what I have to do?
thanks very much...MAX
The setup used for the looks like this (under windows)
C:\classDir -> is the project
C:\classDir\testpackage -> is the only package used (the package "testpackage")
C:\classDir\testpackage\Main.class -> is the class with the main method inside (important: it is the .class and not .java)
The Main.class looks like following:
package testpackage;
public class Main {
public static void main(String[] args) {
System.out.println("Program started! ;-)");
}
}
go with your command prompt to:
c:\classDir> java testpackage.Main
the result:
Program started! ;-)
According to your problems that it starts in your IDE but not from the console:
- checked if you realy use the path to the .class files?
- with the console go to the directory of you .class files, not the project (e.g. in Eclipse it is the bin directory
- enter the full qualified class name (including packages seperated by . -> e.g. testpackage.Main
More infos can be found under:
http://www.oracle.com/technetwork/java/compile-136656.html
Hope it helped
MAX, if the class defines that it's inside the package es_2011, then it should be in a folder with the same name.
So in your case, put the ProgAudioJ.java in the folder es_2011 and then run
javac es_2011\ProgAudioJ.java
latter to run it, you need the command
java es_2011.ProgAudioJ
You should add javac.exe in your path .Edit your path variable and append path to jdk's bin
then put java file in a dir named es_2011 , as the package declaration is es_2011 then compile
c:\es_2011\javac YourJava.java
and now go back to C:
c:\java es_2001.Yourjava
After reading you other Post: "Receiving "wrong name" NoClassDefFoundError when executing a Java program from the command-line" I guess you go to the directory es_2011 where your ProgAudioJ.class file is located and run
java ProgAudioJ
from that folder.
instaend you have to go to the folder above (cd ..) and run
java es_2011.ProgAudioJ
Each package in Java corresponds to a folder on the filesystem. So a package declaration such as com.stackoverflow would mean that the source classes need to be in a folder ./com/stackoverflow. Typically the whole project would have a separate src folder containing com/stackoverflow.
When you compile the Java classes you DO NOT need to put source files in the same directory as javac.exe, you do however need to make sure that javac.exe is in your operating systems PATH variable. This tells the operating system where it should look for executable files when a command is run, on a *nix machine this would usually be /usr/bin or just /bin but on Windows machine the executables normally live within the applications own directories, that is C:\Program Files\something. Assuming that you've installed JDK correctly, the javac.exe should already be in the PATH you can check this by opening the command line and just running javac (just like that). If you get some output then all is well, the system knows where to find javac.exe.
Next you will need to go to your project folder and type javac -d . src/com/stackoverflow/MainSO.java notice that is run from the project folder. This will create a folder called com in your project root and put the compiled classes in com/stackoverflow. The -d flag tells javac where to put the compiled classes, if you leave that out, the compiled classes will be where the sources are.
Then when you want to run the classes you type java com.stackoverflow.MainSO (no .class). Crucially this command will need to be ran in the directory that contains the root of the class hierarchy (that is the com folder containing the compiled classes). You can specify other places for java to look for the classes by providing a classpath to the java command with the -cp flag. By default the classpath will contain the directory the java command was ran in. Should your project have dependencies external .jar files for example you will need to provide every single one of them (with their full filepath) in the classpath (this goes for the compiler as well). The IDEs do this automatically for you.
Hope that helps.