Checked vs Unchecked
Understand the difference between checked and unchecked exceptions in Java.
Checked vs Unchecked is a free Java Academy lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro
Java exceptions come in two families: checked and unchecked. Knowing the difference helps you design methods correctly.
Checked exceptions
Checked exceptions extend Exception (but not RuntimeException). The compiler forces you to handle or declare them with throws.
Code: checked IOException
IOException is checked. You must catch it or declare it in method signature.
public class Main {
public static void main(String[] args) {
try {
java.io.FileReader fr = new java.io.FileReader("missing.txt"); // checked exception
fr.read();
fr.close();
} catch (java.io.IOException e) {
System.out.println("Handled IOException: " + e.getMessage());
}
}
}
Unchecked exceptions
Unchecked exceptions extend RuntimeException. The compiler does not require handling them. Examples: NullPointerException, ArithmeticException.
Code: unchecked NPE
NullPointerException is unchecked. You can catch it, but the compiler does not force you.
public class Main {
public static void main(String[] args) {
String s = null;
try {
System.out.println(s.length()); // unchecked exception
} catch (NullPointerException e) {
System.out.println("Caught NullPointerException");
}
}
}
Code: throws declaration
Checked exceptions can be declared with throws. Callers must handle or propagate them.
public class Main {
static void risky() throws java.io.IOException {
throw new java.io.IOException("I/O problem");
}
public static void main(String[] args) {
try {
risky();
} catch (java.io.IOException e) {
System.out.println("Handled in main: " + e.getMessage());
}
}
}
Checked vs unchecked check
Quick check: Which is true about checked vs unchecked exceptions?
Recap
Recap: Checked exceptions (IOException) must be declared or handled. Unchecked (RuntimeException) are optional to handle.
Frequently asked questions
Is the “Checked vs Unchecked” lesson free?
Yes — the full text of “Checked vs Unchecked” is free to read here on the web, and the Java Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO.
What will I learn in “Checked vs Unchecked”?
Understand the difference between checked and unchecked exceptions in Java. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Java Academy?
No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Checked vs Unchecked” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Java Academy lesson?
Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- try/catch/finally
- Checked vs Unchecked
- Reading Stack Traces