How to Execute a Java Program from the Command Line in Windows

What steps should I follow to run a Java program from the command line on Windows?

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();
        }
    }
}

To run a Java program from the command line on Windows, you need to ensure that you have Java installed and set up correctly. You'll use the Command Prompt to compile and execute your Java program, following these steps:

// To compile and run your Java application:
// Step 1: Open Command Prompt and navigate to the directory containing CopyFile.java
// Step 2: Compile the program:
javac CopyFile.java
// Step 3: Run the compiled class:
java CopyFile
// Ensure input.txt is in the same directory or provide the full path.

Causes

• Java Development Kit (JDK) is not installed or configured correctly.
• Environment variables are not set, particularly the PATH variable.
• The program file is not in the correct directory when you attempt to run it.

Solutions

• Install the latest version of the Java Development Kit (JDK) from the official Oracle or OpenJDK website.
• Ensure the PATH environment variable includes the path to the 'bin' directory of your JDK installation (for example: C:\Program Files\Java\jdk-<version>\bin).
• Open the Command Prompt and navigate to the directory where your Java file is located using the 'cd' command.

Mistake: Not adding Java to the system PATH variable.

Solution: Go to "Control Panel > System and Security > System > Advanced system settings > Environment Variables" and add the JDK bin directory to the PATH.

Mistake: Compiling from a different directory than where the Java file is located.

Solution: Use the 'cd' command in the Command Prompt to change to the directory of the Java file.

Mistake: File not found error when running the program.

Solution: Ensure the input.txt file is present in the same directory or specify the complete path in the Java code.