Run Java Code From Python3

java_runner.py

import subprocess
import tempfile
import os


def run_java_code(java_code: str, *args) -> str:
    """
    Executes a given Java code string as a standalone Java program. This function writes the code
    to a temporary file, executes it using Java's direct execution feature (introduced in Java 11),
    captures the output, and performs cleanup.

    Args:
        java_code (str): A string containing the full Java code. This must include a public class
                         definition. The execution entry point should be in this class.
        *args (tuple): Variable length argument list, where each argument is passed to the
                       Java program as command line arguments. All arguments are converted to strings.

    Returns:
        str: The stdout captured from the Java program after successful execution. If compilation
             or execution fails, returns None and prints an error message to the standard output.

    Raises:
        This function does not raise any exceptions directly but will print error messages
        to standard output in case of compilation or execution errors.
    """

    # Create a temporary file to hold the Java code
    with tempfile.NamedTemporaryFile(
        delete=False, suffix=".java", mode="w", encoding="utf-8"
    ) as java_file:
        java_file.write(java_code)
        java_filename = java_file.name

    try:
        # Prepare the command to run the Java program, converting all arguments to strings
        run_command = ["java", java_filename] + [str(arg) for arg in args]

        # Execute the Java program
        run_result = subprocess.run(
            run_command,
            capture_output=True,
            text=True,
            check=False,  # Handling error checking manually
        )

        if run_result.returncode != 0:
            print(f"[x] Execution failed:\n{run_result.stderr}")
            return None

        return run_result.stdout
    finally:
        # Clean up: remove the temporary Java file
        if os.path.exists(java_filename):
            os.remove(java_filename)

# Example Java code that should be correctly named according to its public class
java_code = """
public class Temp {
    public static void main(String[] args) {
        System.out.println("Hello from Java!");
    }
}
"""

# Running the provided Java code
if output := run_java_code(java_code):
    print(output)

Starting with Java 11, you can run a single-file program directly using java <filename>.java. This feature simplifies the process for small programs or scripts by implicitly compiling and running the Java code in one step.