I have done a lot of researching on this concept but I can't seem to run a java program on the command prompt. Let's say we had a simple program like this:
public class Hello_World {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
On the command prompt I tried:
javac Hello_World.java
But I get:
'javac' is not recognized as an internal or external command, operable program or batch file
So I compiled it on BlueJ and then did this:
java Hello_World.java
But it said "cannot load or find main class Hello_World"!
I am currently using Windows 7, and made the programs on Notepad++ and BlueJ (to compile).
Any suggestions? Thanks!
This explains in detail what you have to do to set class path. Primarily you need to set your environment variables so that your shell finds the right directory containing javac to compile your program
javac' is not recognized ..
comes when you haven't point your java bin directory to your path environment variable. Because bin directory is the place where javac.exe exist.
To do it.
1) right click on mycomputer property
2) go to Advance system settings.
3) go to environment variable.
4) In system variable click on path
5) go to edit mode and provide your path to java bin directory.
in my case it is C:\Program Files\Java\jdk1.7.0_01\bin;
'javac' is not recognized as an internal...
means OS does not know where javac program is located. Either add it to PATH or run explicitly
my\path\to\file\javac Hello_World.java
Compiling will convert *.java to *.class
Hello_World.class file should be located according to it's package directive. Since you have no one, in your case it should be located in the same directory you will run java.
To run your class specify it's name not file name
java Hello_world
looking for the class is essential part of launching and occurs by rules.
Related
I'm trying to execute a Java program from the command line in Windows. Here is my code:
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
public class CopyFile
{
public static void main(String[] args)
{
InputStream inStream = null;
OutputStream outStream = null;
try
{
File afile = new File("input.txt");
File bfile = new File("inputCopy.txt");
inStream = new FileInputStream(afile);
outStream = new FileOutputStream(bfile);
byte[] buffer = new byte[1024];
int length;
// copy the file content in bytes
while ((length = inStream.read(buffer)) > 0)
{
outStream.write(buffer, 0, length);
}
inStream.close();
outStream.close();
System.out.println("File is copied successful!");
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
I'm not sure how to execute the program - any help? Is this possible on Windows? Why is it different than another environment (I thought JVM was write once, run anywhere)?
Source: javaindos.
Let's say your file is in C:\mywork\
Run Command Prompt
C:\> cd \mywork
This makes C:\mywork the current directory.
C:\mywork> dir
This displays the directory contents. You should see
filenamehere.java among the files.
C:\mywork> set path=%path%;C:\Program Files\Java\jdk1.5.0_09\bin
This tells the system where to find JDK programs.
C:\mywork> javac filenamehere.java
This runs javac.exe, the compiler. You should see nothing but the
next system prompt...
C:\mywork> dir
javac has created the filenamehere.class file. You should see
filenamehere.java and filenamehere.class among the files.
C:\mywork> java filenamehere
This runs the Java interpreter. You should then see your program
output.
If the system cannot find javac, check the set path command. If javac
runs but you get errors, check your Java text. If the program
compiles but you get an exception, check the spelling and
capitalization in the file name and the class name and the java
HelloWorld command. Java is case-sensitive!
To complete the answer :
The Java File
TheJavaFile.java
Compile the Java File to a *.class file
javac TheJavaFile.java
This will create a TheJavaFile.class file
Execution of the Java File
java TheJavaFile
Creation of an executable *.jar file
You've got two options here -
With an external manifest file :
Create the manifest file say - MANIFEST.mf
The MANIFEST file is nothing but an explicit entry of the Main Class
jar -cvfm TheJavaFile.jar MANIFEST.mf TheJavaFile.class
Executable by Entry Point:
jar -cvfe TheJavaFile.jar <MainClass> TheJavaFile.class
To run the Jar File
java -jar TheJavaFile.jar
Complile a Java file to generate a class:
javac filename.java
Execute the generated class:
java filename
In case your Java class is in some package. Suppose your Java class named ABC.java is present in com.hello.programs, then you need to run it with the package name.
Compile it in the usual way:
C:\SimpleJavaProject\src\com\hello\programs > javac ABC.java
But to run it, you need to give the package name and then your java class name:
C:\SimpleJavaProject\src > java com.hello.programs.ABC
Since Java 11, java command line tool has been able to run a single-file source-code directly. e.g.
java HelloWorld.java
This was an enhancement with JEP 330: https://openjdk.java.net/jeps/330
For the details of the usage and the limitations, see the manual of your Java implementation such as one provided by Oracle: https://docs.oracle.com/en/java/javase/11/tools/java.html
Assuming the file is called "CopyFile.java", do the following:
javac CopyFile.java
java -cp . CopyFile
The first line compiles the source code into executable byte code. The second line executes it, first adding the current directory to the class path (just in case).
It is easy. If you have saved your file as A.text first thing you should do is save it as A.java. Now it is a Java file.
Now you need to open cmd and set path to you A.java file before compile it. you can refer this for that.
Then you can compile your file using command
javac A.java
Then run it using
java A
So that is how you compile and run a java program in cmd.
You can also go through these material that is Java in depth lessons. Lot of things you need to understand in Java is covered there for beginners.
You can compile any java source using javac in command line ; eg, javac CopyFile.java.
To run : java CopyFile.
You can also compile all java files using javac *.java as long as they're in the same directory
If you're having an issue resulting with "could not find or load main class" you may not have
jre in your path. Have a look at this question:
Could not find or load main class
On Windows 7 I had to do the following:
quick way
Install JDK http://www.oracle.com/technetwork/java/javase/downloads
in windows, browse into "C:\Program Files\Java\jdk1.8.0_91\bin" (or wherever the latest version of JDK is installed), hold down shift and right click on a blank area within the window and do "open command window here" and this will give you a command line and access to all the BIN tools. "javac" is not by default in the windows system PATH environment variable.
Follow comments above about how to compile the file ("javac MyFile.java" then "java MyFile") https://stackoverflow.com/a/33149828/194872
long way
Install JDK http://www.oracle.com/technetwork/java/javase/downloads/index.html
After installing, in edits the Windows PATH environment variable and adds the following to the path C:\ProgramData\Oracle\Java\javapath. Within this folder are symbolic links to a handful of java executables but "javac" is NOT one of them so when trying to run "javac" from Windows command line it throws an error.
I edited the path: Control Panel -> System -> Advanced tab -> "Environment Variables..." button -> scroll down to "Path", highlight and edit -> replaced the "C:\ProgramData\Oracle\Java\javapath" with a direct path to the java BIN folder "C:\Program Files\Java\jdk1.8.0_91\bin".
This likely breaks when you upgrade your JDK installation but you have access to all the command line tools now.
Follow comments above about how to compile the file ("javac MyFile.java" then "java MyFile") https://stackoverflow.com/a/33149828/194872
STEP 1: FIRST OPEN THE COMMAND PROMPT WHERE YOUR FILE IS LOCATED. (right click while pressing shift)
STEP 2: THEN USE THE FOLLOWING COMMANDS TO EXECUTE.
(lets say the file and class name to be executed is named as Student.java)The example program is in the picture background.
javac Student.java
java Student
As of Java 9, the JDK includes jshell, a Java REPL.
Assuming the JDK 9+ bin directory is correctly added to your path, you will be able to simply:
Run jshell File.java — File.java being your file of course.
A prompt will open, allowing you to call the main method: jshell> File.main(null).
To close the prompt and end the JVM session, use /exit
Full documentation for JShell can be found here.
Now (with JDK 9 onwards), you can just use java to get that executed.
In order to execute "Hello.java" containing the main, one can use:
java Hello.java
You do not need to compile using separately using javac anymore.
You can actually run Java program as you would shell or python scripts without manually compile the Java file, as described in
JEP 330. That is available since JDK 11.
If you create a file testing, and put the following you should be able to run it as command testing. You need to make it executable in Linux and Mac OSX with chmod +x testing.
#!/usr/bin/env java --source 11
public class Test {
public static void main(String [] args) {
System.out.println("Hello world!");
System.exit(0);
}
}
You are not allowed to use the file extension .java in the previous example.
$ chmod +x testing
$ ./testing
Hello world!
$
But you can still execute if it is was name Test.java without the shebang "#!" prefix like this:
public class Test {
public static void main(String [] args) {
System.out.println("Hello again!");
System.exit(0);
}
}
Then execute the file Test.java with following command:
$ java Test.java
Hello again!
$
So this works as long as you have a new enough Java compiler in the path, check with java -version. More information in this blog.
I am trying my had at java programming and I made a HelloWorld program and if you need the code its right here:
public class Main {
public static void main(String[] args){
System.out.println("helloworld");
}
}
It compiled without error and whenever I try to run it from the command prompt it says:
"Error: Could not find or load main class".
I don't know what I'm doing wrong. I have the jre 1.8.0_45 and jdk 1.7.0_71.
As per your comment
I navigate to the location of the .class and type "java
helloworld.class" – Takdm
you don't .class when you run the program. Just do
java helloworld
First- the file name and the class name must be identical.
Then compile your program using javac FileName.java command
To run your program try- java -cp . ClassName
Should work.
Adding . to CLASSPATH variable in Environment variables solved my problem!!
Java searches for the classes in the paths mentioned in the CLASSPATH variable if you don't add . there, it won't search for classes in the current working directory!!!
Go to Control panel > System and Security > System > Advanced System Settings > Advanced
Click Environment Variables
If the CLASSPATH variable is present under User variables, add '.' separated by a semicolon. For example, if Java is installed in C:\Program Files\Java\jdk1.8.0_131\bin , CLASSPATH will be
C:\Program Files\Java\jdk1.8.0_131\bin;.;
Click OK.
I'm very new to programming so let me just explains where I'm at:
I have downloaded the most recent JDK
I have changed the path variable in the environmental variables tab, javac does run by itself in the command prompt
I have downloaded notepad++
So I created a very simple program, pretty much just a simple "hello world" deal...
public class pleaseWork {
public static void main (String[] args) {
System.out.println("Please work");
}
}
And saved it into a folder I have on my C drive but not anywhere in the java folder. I have it saved as pleaseWork.java.
So I go to the command line and if I just type javac it runs correctly, but if I type in javac pleaseWork.java I get an error -
javac: file not found: pleaseWork.java
So basically I'm asking if I need to save my notepad++ .java files in a certain place for them to compile in the command prompt or is it something else?
Error javac: file not found: pleaseWork.java indicate that your javac command not able to locate file you have given in your command that is pleaseWork.java.
To compile file place in any folder you need to go upto the path where your JAVA file place, from that path execute command javac pleaseWork.java.
You are executing your javac command from the directory path where this java file is not present.
Another way is
You need to specify the full file path in the argument.
e.g javac "C:\temp\pleaseWork.java"
For more info visit How to Run JAVA file from command promt.
when you go to command prompt... first of all go back to c drive and set the path there. and compile it... and while saving program in notepad... please provide file name in double quotes like "programWorld.java" or else it will be saved as text file not java file. resulting in file not found error
Make sure javac is in your path (so you can run it from anywhere). Then in your command prompt cd to the directory where your pleaseWork.java file is saved and call javac from there.
As an aside, it's standard form to name your classes and files in java starting with a capital letter (PleaseWork.java)
To set the temporary path of JDK, you need to follow following steps: Try this and let me know if its still not working, then c:>cd yourNewFolderName then set path
Open command prompt
copy the path of jdk/bin directory
write in command prompt: set path=copied_path
For Example:
set path=C:\Program Files\Java\jdk1.6.0_23\bin
I am very new to linux environment.
I am trying to run an simple hello world java class in linux environment.
Hello .java
package com.util;
public class Hello {
/**
* #param args
*/
public static void main(String[] args) {
System.out.println("hi");
}
}
I have compiled java class in windows environment and uploaded the .class file to linux system into /home/scripts path.
my command is as follows,
java -cp /home/scripts com.util.Hello
when i am executing this command from this same /home/scripts where Hello.class is there i am getting,
Error: Could not find or load main class com.util.Hello and not able to proceed further.
can some one help me in this issue?
navigate to /home/scripts using terminal
javac com/util/Hello.java
then
cd /home/scripts
java -cp . com.util.Hello
Or,
java -cp "/home/scripts" com.util.Hello
At first you must generate your .class file :
javac ./hello.java
This command has generated hello.class file
And after you can run your class file ! :)
java hello
We first know javac command work well.
I also met this error,and i have resolved this.Let me share this.
First we need to find the parent path of your package in your java codes.
Then cd to that path using java package + fileName should work well at that moment.
I had the exact same issue on windows, and I solved it by adding path "." to both CLASSPATH and PATH, maybe you can try this on Linux as well.
Your .class file should not reside in /home/scripts/, but in /home/scripts/com/util/. Take a look at this document that explains the relation between classpath, packages and directories.
Before Specifying the path,ensure you follow these three things meticulously,
1. Close the command prompt window, before specifying the path.
2. When adding path, add bin and semi- colon at the end and
3. If JAVAC command has worked properly, try java -cp class name.
if you want to run program in current working directory where your class reside.
java gives three options.
first option
java -cp Tester
Second option for current working directory
java -cp . Tester
Third option export CLASSPATH variable
export CLASSPATH=$CLASSPATH:. (this is the best one if your directory changes) or
export CLASSPATH=$PWD
or
export CLASSPATH=
after that you must sorce the bashrc or bashprofile.
I'm new in programming, I'm learning Java right now. I tried to use the javac command, but the environment says that javac is an unknown command.
How to use "javac" to compile .java files from the command prompt? I'm using eclipse 1.2.2.20100216-1730, JRE 1.6 and JRE6
The JRE has the "java" program for running programs already compiled. The "javac" program is only in the JDK. Download and install the JDK. If BTW it still gives you the same error, then you need to add the javac directory to your PATH environment variable.
Before the Java virtual machine (VM) can run a Java program, the program's Java source code must be compiled into byte-code using the javac compiler. Java byte-code is a platform independent version of machine code; the target machine is the Java VM rather than the underlying architecture. To compile a Java source code file add.java, you would do the following:
javac add.java
If there are no errors in your source file, the Java compiler will produce one or more .class files (one .class file for each class defined in the add.java source file). For example, the results of a successful compile of Foo.java will produce a byte-code version of the class in a file named Foo.class.
Every public class that you write must be in a separate .java file where the first part of the file name is identical to the class name. The .java file additionally can contain code for protected and private classes.
Once you have successfully compiled your Java source code, you can invoke the Java VM to run your application's byte-code:
java <class with main method to run> [<command line args>, ...]
For example, to run the main method from the Foo class:
java Foo
Any command line arguments (arguments to add's main method) follow the class name:
java add 10 20
Such Error may occur due to two reasons:
You have not installed java jdk on your system.
You have not set the environment variables.classpath ,path.
Setting Path and classPath:
Windows XP
Select Start, select Control Panel. double click System, and select the Advanced tab.
Click Environment Variables. In the section System Variables, find the PATH environment variable and select it.
Click Edit. If the PATH environment variable does not exist, click New.
In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.
Windows Vista:
From the desktop, right click the My Computer icon.
Choose Properties from the context menu.
Click the Advanced tab (Advanced system settings link in Vista).
Click Environment Variables. In the section System Variables, find the PATH environment variable and select it.
Click Edit. If the PATH environment variable does not exist, click New.
In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.
If you have not set the classpath and path you can access javac giving full path:
such as C:\Java\jdk1.7.0\bin\javac MyClass.java
To check the path and classpath, type these commands in a command window:
echo $PATH
echo $CLASSPATH
If you get a blank command line in response to either of these, then that particular variable has no value (it has not yet been set).
setting path and classpath through cmd:
set path=c:\j2sdk1.4.1_01\bin(Give the path of bin)
set classpath=;(or the directory where you want your class files)
Download and install JDK
set environment path --> edit path in environment path and add ;/bin
using javac command --> javac *.java or javac ClassName.java
When run the main method you should note to [package] name
java packagename.ClassName