Complete List of Unchecked Exceptions in Java

In Java, unchecked exceptions are the exceptions that occur during runtime and are not checked by the compiler. These exceptions are subclasses of RuntimeException, and the Java compiler doesn’t force you to catch or declare them using throws.

Unchecked exceptions typically occur due to programming errors like bad logic, null access, invalid type casting, or improper use of collections. While they can crash your application if not handled properly, understanding them helps you write more robust and bug-free code.

In this guide, we’ve organized all the major unchecked exceptions in Java into clear categories—so you can quickly learn, recognize, and handle them effectively.

Unchecked Exceptions in Java – Complete List with Descriptions

1. Arithmetic and Number-Related Exceptions

Examples:

int a = 10 / 0; // ArithmeticException
Integer.parseInt("abc"); // NumberFormatException
System.out.printf("%d", "hello"); // IllegalFormatConversionException

2. 📦 Array and Collection-Related Exceptions

Examples:

int[] a = new int[3];
a[5] = 10; // ArrayIndexOutOfBoundsException

ArrayList<String> list = new ArrayList<>();
list.get(1); // IndexOutOfBoundsException

3. 🧵 Threading and Synchronization Exceptions

Examples:

Thread t = new Thread();
t.start();
t.start(); // IllegalThreadStateException

4. 🧑‍💻 Null and Type-Related Exceptions

Examples:

String s = null;
s.length(); // NullPointerException

Object obj = "test";
Integer i = (Integer) obj; // ClassCastException

5. 🛠️ Illegal Usage or Configuration Exceptions

Examples:

Thread t = new Thread();
t.setPriority(11); // IllegalArgumentException

List<String> list = Collections.unmodifiableList(new ArrayList<>());
list.add("item"); // UnsupportedOperationException

6. 🎛️ Formatting and Input Exceptions

7. 🌍 Resource and Reflection-Related Exceptions

🔄 Summary Table by Category

📝 Bonus Tip: Custom Unchecked Exceptions

You can create your own unchecked exceptions like this:

class InvalidAgeException extends RuntimeException {
    public InvalidAgeException(String msg) {
        super(msg);
    }
}