How do I run a Java program from the command line on Windows?

Question

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)?

Answer 1

To complete the answer :

1. The Java File

   TheJavaFile.java
   

2. Compile the Java File to a *.class file

   javac TheJavaFile.java
   

   • This will create a TheJavaFile.class file

3. Execution of the Java File

   java TheJavaFile
   

4. Creation of an executable *.jar file

   • You've got two options here -

     1. 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

     2. Executable by Entry Point:

        • jar -cvfe TheJavaFile.jar <MainClass> TheJavaFile.class

5. To run the Jar File

   java -jar TheJavaFile.jar
   

Answer 2

Complile a Java file to generate a class:

javac filename.java

Execute the generated class:

java filename

Answer 3

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

Answer 4

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

Answer 5

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).

Answer 6

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.

Answer 7

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

Answer 8

On Windows 7 I had to do the following:

quick way

1. Install JDK http://www.oracle.com/technetwork/java/javase/downloads
2. 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.
3. Follow comments above about how to compile the file ("javac MyFile.java" then "java MyFile") https://stackoverflow.com/a/33149828/194872

long way

4. Install JDK http://www.oracle.com/technetwork/java/javase/downloads/index.html
5. 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.
6. 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".

7. This likely breaks when you upgrade your JDK installation but you have access to all the command line tools now.

8. Follow comments above about how to compile the file ("javac MyFile.java" then "java MyFile") https://stackoverflow.com/a/33149828/194872

Answer 9

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

Answer 10

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:

1. Run jshell File.java — File.java being your file of course.
2. A prompt will open, allowing you to call the main method: jshell> File.main(null).
3. To close the prompt and end the JVM session, use /exit

Full documentation for JShell can be found here.

Answer 11

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.

Answer 12

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.