Working with Files and I/O in Java

Programs don’t just live in their own little bubble — they need to talk to the outside world. Sometimes that means reading a file, writing one, or asking the user for input. Welcome to Input/Output (I/O) in Java.

Why I/O Matters

• x>Load configuration from files
• x>Save user data
• x>Read logs, CSVs, and data sets
• x>Automate tasks like generating reports

I/O is everywhere. And Java gives you a lot of tools to work with it.

Getting Input from the User

We’ve done this before — but here’s a simple example using Scanner again:

Scanner can read text, numbers, tokens — from the keyboard or even files.

Reading Files

Let’s say you have a text file called data.txt.

Don't forget to close() the Scanner when done!

Writing to Files

Want to save some text into a file? Try this:

This will create (or overwrite) output.txt with your content. Use FileWriter(true) to append instead of overwrite.

I/O and Exceptions

File operations can fail. That’s why we surround them with try/catch blocks.

You’ll encounter:

• x>FileNotFoundException
• x>IOException
• x>Permissions issues

I/O almost always means checked exceptions. You must handle or declare them.

Alternatives and Utilities

Java has many other I/O tools:

• x>BufferedReader and BufferedWriter — for large text files
• x>Files (from java.nio.file.*) — super handy for modern file operations
• x>PrintWriter — easy file writing with formatting

You’ll encounter these more in future projects, but now you know the basics.

Mini Challenge

Write a program that:

Try it out!

What’s Next

You’ve learned how your code interacts with the outside world. But now it’s time to look inward — at how to structure your code for reuse and flexibility. In the next chapter, we’ll dive into object-oriented design concepts that make your programs more powerful and maintainable.