Java Exceptions

try, catch, finally and throw.

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Exceptions signal errors at runtime.

try { } catch (ExceptionType e) { } finally { }
throw new IllegalArgumentException("message");
Checked exceptions (like IOException) must be caught or declared with throws.
Unchecked exceptions (RuntimeException and subclasses) do not have to be.
Try-with-resources closes files and connections automatically: try (var r = new FileReader(f)) { }

Key Takeaways: Java Exceptions

Mastering Java Exceptions helps you write clean and reliable Java code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

Java Exceptions Code Example

Java

public class Main {
    static int divide(int a, int b) {
        if (b == 0) throw new ArithmeticException("Cannot divide by zero");
        return a / b;
    }

    public static void main(String[] args) {
        try {
            System.out.println(divide(10, 2));
            int[] nums = {1, 2, 3};
            System.out.println(nums[5]);
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Bad index: " + e.getMessage());
        } finally {
            System.out.println("Finished");
        }

        try {
            divide(1, 0);
        } catch (ArithmeticException e) {
            System.out.println(e.getMessage());
        }
    }
}

Output

5
Bad index: Index 5 out of bounds for length 3
Finished
Cannot divide by zero

Run this example on your own computer. The "Get Started" lesson shows how to set it up.

Java Exceptions Practice Exercises

Check what you learned in “Java Exceptions”.

/ 2 solved

Fill in the blank

Handle the exception.

try {
  risky();
}  (Exception e) {
}

✓ Correct! Not quite. Try again.

Multiple choice

Checked exceptions must be…

caught or declared with throws ignored printed converted to strings

✓ Correct! Not quite. Try again.

to save your exercise progress.

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Java Exceptions

💡 Key Takeaways: Java Exceptions

Java Exceptions Code Example

Java Exceptions Practice Exercises

Key Takeaways: Java Exceptions