Building a Number Processor: Part 1

Today's Goal

Starter code: here

We're going to build a program that takes user input and converts it into a number. This might sound simple, but it teaches us several important programming concepts that we'll use throughout our coding journey.

Understanding String Input

When someone types something into a JOptionPane dialog, Java sees it as text (a String), even if they type numbers. Think of it like receiving a note - even if someone writes "42" on the paper, it's still just marks on paper until we interpret it as a number.

String userInput = JOptionPane.showInputDialog("Enter a number:");

Converting Strings to Numbers

Java provides tools to convert text into numbers. The main one we'll use today is Integer.parseInt(). This method tries to convert a String into a whole number.

Integer.parseInt("123")   // Seems straightforward...
Integer.parseInt("abc")   // But what about this?
Integer.parseInt("")      // Or this?
Integer.parseInt("3.14")  // Or even this?

Protecting Our Program with Input Validation

Good programs don't crash when users make mistakes. Instead, they provide helpful feedback. Before we even try to convert a String to a number, we should check:

Is there any input at all? If someone just hits "OK" without typing anything, we get an empty String (or possibly null). We should check for this first.

if (input == null || input.trim().isEmpty()) {
    return "Please enter a number";
}

Handling Conversion Errors

When we try to convert a String to a number, things might go wrong. Java uses something called "exceptions" to tell us about these problems. We can catch these exceptions and handle them gracefully:

try {
    int number = Integer.parseInt(input);
    // If we get here, the conversion worked!
} catch (NumberFormatException e) {
    // If we get here, something went wrong
}

Your Task

Complete the process() method in the NumberProcessor class. Your method should:

1. Check if the input is null or empty

2. Try to convert the input to an integer

3. Return appropriate messages for success or failure