How to Safely Check Command Line Arguments in Java

How can I safely check if command line arguments are valid in Java?

public static void main(String[] args) {
    if (args.length == 0) {
        System.out.println("Proper Usage is: java program filename");
        System.exit(0);
    }
    // Additional processing of args[0]
}

Validating command line arguments in Java is crucial to prevent exceptions and ensure your program runs correctly. The provided code snippet checks for null, which can lead to an ArrayIndexOutOfBoundsException if no arguments are provided. This article provides a proper way to handle command line arguments safely.

public static void main(String[] args) {
    // Check if arguments are provided
    if (args.length == 0) {
        System.out.println("Proper Usage is: java program filename");
        System.exit(0);
    }
    String filename = args[0]; // Safely access first argument
    // Process filename accordingly
}

Causes

• Null pointer exceptions might occur when accessing elements of the array without checking its length.
• Accessing an index that doesn't exist leads to ArrayIndexOutOfBoundsException.

Solutions

• Check if the length of the array 'args' is greater than zero before accessing its elements.
• Provide user instructions when no arguments are given to improve user experience.

Mistake: Not checking array length before accessing elements.

Solution: Always check if the 'args.length' is greater than zero to avoid exceptions.

Mistake: Assuming command line arguments are always provided.

Solution: Prompt the user with proper usage instructions when arguments are missing.