I'm trying to implement the following:
public class Main {
public static void main(String[] args) {
//READ FILE IN
String filename = args[0];
System.out.println(filename);
}}
This compiles fine, but when I try to run java br/com/seimos/minijava/Main.java < a or java br/com/seimos/minijava/Main.java a for example, I get an error. Why?? (by the way, I need to get it so that I can do java br/xx/xx.../xx.
Thanks!
EDIT: Sorry, I typed it wrong initially. I DID run java not javac.
The error I get is:
Exception in thread "main" java.lang.NoClassDefFoundError: br/com/seimos/minijava/Main/java
Caused by: java.lang.ClassNotFoundException: br.com.seimos.minijava.Main.java
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
You don't pass arguments at compile-time, but at runtime.
javac --> compiles your Java program
java --> runs the generated bytecode
java br/com/seimos/minijava/Main.java -args
^ remove (.java)
Java runtime runs the .class bytecode-generated, which is of the name supplied, not the uncompiled .java source
Running a Java program is a two step process. First the .java file is compiled into .class files. Then you use the java command to execute the class files. Runtime arguments must obviously be passed at runtime when you invoke java.
For compiling, if the java file is with some package, you need to apply such as br.com.xxx.main.java. If that is just path to the java file that is ok. can you post the error?
Related
I am newbie in java. I am running java programs via Ubuntu terminal
I just started java package topic and have been dealing with a problem for several hours.
I tried to create a simple package called pack which has single class Hello.
I created a directory pack. Inside the pack I put Hello.class file intp pack directory via
javac -d ./pack Hello.java
command.
Then I included pack package into a class containing main method. The class's name is test and it is located in test.java file This class is located in another directory. I compile via
javac -cp ./pack test.java
It compiles without any error and everything is ok.
However, when I enter command
java -cp ./pack test
it gives me
Error: Could not find or load main class test
When I tried
java test
command. The following message showed up
Exception in thread "main" java.lang.NoClassDefFoundError: pack/Hello
at test.main(test.java:6)
Caused by: java.lang.ClassNotFoundException: pack.Hello
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
... 1 more
Can anybody explain me what I am doing wrong? Any help is much appreciated.
Sorry, I did bot include my source codes. Here they are.
import pack.Hello;
public class test
{
public static void main(String args[])
{
Hello.HelloMessage();
}
}
This is test.java file which tests if everything is ok. It is located at
/home/uesername/apps
directory.
Then I created "pack" directory. Full path to the pack directory is
home/username/apps/pack
Inside the "pack" I put Hello.java file. The content of Hello.java file is
package pack;
public class Hello
{
public static void HelloMessage()
{
System.out.println("hello, world");
}
}
To begin with I suggest you use an IDE to setup you environment for compiling, running and debugging.
The problem you have is that you have compiled with the wrong path.
javac -cp . pack/Hello.java
javac -cp . pack/test.java
and
java -cp . pack.Hello
or
java -cp . pack.test
The problem is that you compiled a class with package pack in a directory pack and you would end up with
pack/pack/Hello.class
I suggest you check where the Hello.class file has been placed.
java.lang.NoClassDefFoundError
I have a java program which is dependant on two jar files.
i compile the program using command :
javac -classpath jar1.jar:jar2.jar myprog.java and it compiles successfully.
But when i try to run the program using command : java -cp jar1.jar:jar2.jar myprog , it is throwing the java.lang.NoClassDefFoundError . please help , where am i wrong ?
i am using ubuntu 10.04.
Actual error :
Exception in thread "main" java.lang.NoClassDefFoundError: userapps/SelectionTask_classes/SelectionTask
Caused by: java.lang.ClassNotFoundException: userapps.SelectionTask_classes.SelectionTask
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: userapps/SelectionTask_classes/SelectionTask. Program will exit.
where SelectionTask is my class file generated after successful compilation.
Make sure that the current directory is also in the classpath. Try running with:
java -cp .:jar1.jar:jar2.jar myprog
if your compiled class file myprog.class is in the current directory.
(This assumes that your program is not in a package).
You need to add directory where your compiled java program (*.class) file is located. If it's in current directory then you could run it like this (notice "." which denotes current working directory):
java -cp .:jar1.jar:jar2.jar myprog
Look at the error, it's complaining about not being able to find "userapps.SelectionTask_classes.SelectionTask", which hints at the last entry in your classpath not beign specified correctly. Now, assuming that the JAR files you have specified are in the following directory structure:
./hadoop-0.20.1-core.jar
./lib/hadoopdb.jar
./userapps/SelectionTask_classes/
You would run:
java -cp hadoop-0.20.1-core.jar:lib/hadoopdb.jar:userapps/SelectionTask_classes/ myprog
I'm following the java tutorials on the Princeton website.
I'm running debian sqeeze 64bit and I have installed Sun java version 6.
I can compile and run the basic hello world program without any problem, using the terminal and the Eclipse IDE.
The problem is:
when I try to compile and run a program, which requires an argument input for example:
public class RandomSeq {
public static void main(String[] args) {
// command-line argument
int N = Integer.parseInt(args[0]);
// generate and print N numbers between 0 and 1
for (int i = 0; i < N; i++) {
System.out.println(Math.random());
}
}
}
I can run this on Eclipse putting an integer argument, however it doesn't work on the terminal.
I get this error:
emes#debian:~/Documents/workspace/IOput/src/randomSeq$ java RandomSeq 21
Exception in thread "main" java.lang.NoClassDefFoundError: RandomSeq (wrong name: randomSeq/RandomSeq)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: RandomSeq. Program will exit.
I've tried to update the /etc/profile to include the java-6-sun on the PATH variable.
I'm not sure, what to try from here.
Apparently, you're trying to run your program from the src folder of an Eclipse project. src stands for “source”. The executable version of your program (the compiled classes) is not in src; it's in bin, which stands for “binary”, i.e. machine code.
When using the command line, you should first compile your program:
javac MyClass.java
and then run it:
java MyClass
But please, do not do it inside an Eclipse project's directory structure, or you will create additional files (class files) not expected by Eclipse at this location.
Additionally maybe you are inside a package. You can't run a class if you're within its package folder. You need to be at the top-level of the package hierarchy.
Example: suppose your class is inside a package named mypackage. Then in someFolder/mypackage/MyClass.java you will have something like:
package mypackage;
class MyClass {
...
}
After compiling your code, you must be in somefolder and issue the shell command:
java mypackage.MyClass
It looks as if your class has a package
package randomSeq;
public class RandomSeq {
If so, then when starting it it should be located in the folder randomSeq and the root of that folder should be in your class path and the package must be specified when invoking.
So, if your .class file is in bin/randomSeq then you could run it with java -cp bin randomSeq.RandomSeq 21
Don't bother about the argument as that would give a run-time null pointer exception.
The problem is your classpath.
Make a list (ls or dir) in the directory you run java RandomSeq from.
Do you have a .class file there. If not run javac RandomSeq.java first to generate the class file
I have downloaded a java developers kit for my 64bit windows 7, wrote down my code in the notepad, though the code is compiling from the command prompt and creating a .class file, but its refusing to run showing the error code:
java.lang.NoClassDefFoundError: first Caused by: java.lang.ClassNotFoundException: first
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
Could not find the main class: first. Program will exit. Exception in thread "main"
I have made sure more than once that the file name and the class name are exactly same(i have kept them smallcase 'a' just to be sure). But still no avail, could you please suggest a few solutions please.. I'm new to java i'm basically a C/C++ programmer.
A java program has this basic structure:
ClassName.java
public class ClassName
{
public static void main(String[] args)
{
}
}
try using this outline to generate your code.
compile and run with:
javac ClassName.java
java ClassName
I used to get this error when I ran a Class file.
Try doing: java NameOfClass
You don't need the .java extension when running, but you need it for compiling. That was always the problem I used to have.
Did you set your classpath?
http://download.oracle.com/javase/1.3/docs/tooldocs/win32/classpath.html
java -classpath <path> <classname>
You must provide with the code.
Anyway, from the Java Docs, class ClassNotFoundException:
Thrown when an application tries to
load in a class through its string
name using:
The forName method in class Class.
The findSystemClass method in class ClassLoader.
The loadClass method in class ClassLoader.
but no definition for the class with the specified name
could be found.
Must read link : Tip: Causes of java.lang.ClassNotFoundException
It is quite possible after compiling your code you would be writing java filename.java.
Because this sought of exception occurs then.
After compiling your program using javac filename.java use the command to start your interpreter java filename.
As you enter this command java interpreter automatically starts interpreting filename.class.
commands :
javac filename.java // to start compiling
java filename // to start interpreting
I'm using the JDK 3.1. I am using XML Publisher. I'm getting this error:
Could not find the main class. Program will exit.
After I click on "OK", I get
Java execution failed. Please check the Java Option in the option dialog
Sounds like you're trying to execute .jar file and there's no Main-Class entry in the manifest file. Other than that obvious point, your question does not give much information for assistance.
Your question is tricky to understand, but I'm guessing that you haven't actually compiled your Java code, or your compiled code isn't on the classpath.
When I try and execute a non-existent class (this would work if there was a MyClass.class on the classpath with a main() method):
paul#paul-laptop:~$ java MyClass
Exception in thread "main" java.lang.NoClassDefFoundError: MyClass
Caused by: java.lang.ClassNotFoundException: MyClass
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
Could not find the main class: MyClass. Program will exit.
Is that what you're seeing? If so:
compile your class with javac if you haven't done so
check that your classpath includes the location of the class
(You can specify the classpath explicitly when you execute the java program using -classpath, check the documentation for details.)
I include this answer as someone who has made an error someone consuming java rather than programming in it would make:
On the command line when executing a JAR file, be sure your line reads
java -jar whatever.jar
instead of
java whatever.jar
Without the -jar you sometimes get the "Could not find the main class" error.
Here are some good answers What does "Could not find or load main class" mean?
But, I will share one possibility I had. I used the JDK1.7 to compile my code and run the jar package using the JDK1.6, the error is:
Could not find the main class. Program will exit.
So, check if the JDK version you used to run your code is lower than that used to compile your code.
Check this website: "Could not find main class" error when previewing BI Publisher for Word. It directly references Java issues with Oracle BI Publisher Plugins for Word.
It basically says that you need to set your Java Home by going to Options in the BI Publisher Tab in the MS Office Ribbon.