Java Exception Handling Guide

Exceptions in Java

Exceptions signal errors during execution. Java uses try/catch/finally and distinguishes checked vs unchecked exceptions.

try/catch/finally

try {
    int[] arr = new int[3];
    arr[5] = 10; // throws
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Bad index: " + e.getMessage());
} finally {
    System.out.println("Always runs");
}

Checked vs Unchecked

Type	Must handle?	Example
Checked	Yes (compile)	IOException
Unchecked	No	NullPointerException

Throwing Exceptions

public void setAge(int age) {
    if (age < 0) throw new IllegalArgumentException("Age < 0");
}

try-with-resources

try (BufferedReader r = new BufferedReader(new FileReader("f.txt"))) {
    return r.readLine();
} // file auto-closed

FAQs

Should I catch Exception broadly?

No — catch specific types. Broad catches hide bugs. More in our Java section.

What is the finally block for?

Cleanup that must run whether or not an exception occurred.