Checked and Unchecked Exception in Java With Example

In this post, we will discuss the difference between checked and unchecked exceptions in Java with examples.

Checked Exceptions

Definition: Exceptions that are checked at compile-time are called checked exceptions. 

Subclass of: Directly or indirectly derived from java.lang.Exception but not from java.lang.RuntimeException. 

Handling Requirement: A checked exception must be handled either by re-throwing or with a try-catch block.

Purpose: Represent abnormal situations that can occur in the program and which can be reasonably anticipated and recovered from. Examples: FileNotFoundException, IOException, ClassNotFoundException. 

Recovery: Developers are expected to provide recovery mechanisms for these exceptions.

Example: Reading from a file that doesn't exist will throw a FileNotFoundException, which is a checked exception. 

import java.io.*;

public class CheckedExample {
    public static void main(String[] args) {
        try {
            BufferedReader reader = new BufferedReader(new FileReader("nonExistentFile.txt"));
            String line = reader.readLine();
            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }
            reader.close();
        } catch (FileNotFoundException e) {
            System.out.println("Error: " + e.getMessage());
        } catch (IOException e) {
            System.out.println("IO Error: " + e.getMessage());
        }
    }
}

Output:

Error: nonExistentFile.txt (No such file or directory)

Unchecked Exceptions

Definition: Exceptions that are not checked at compile-time but are checked at runtime are called unchecked exceptions. 

Subclass of: Derived from java.lang.RuntimeException and java.lang.Error. 

Handling Requirement: Unchecked exception isn’t required to be handled.

Purpose: Mainly arise due to programming mistakes, incorrect assumptions, or logical errors.

Examples: NullPointerException, ArrayIndexOutOfBoundsException, ArithmeticException. 

Recovery: Often, the best remedy is to fix the code that led to the exception rather than attempting recovery during runtime.

Example: Attempting to access an index of an array that doesn't exist will result in ArrayIndexOutOfBoundsException, which is an unchecked exception.

public class UncheckedExample {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3};
        
        try {
            System.out.println("Value at index 5 is: " + arr[5]);
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Output:

Error: Index 5 out of bounds for length 3

Difference Between Checked and Unchecked Exceptions in Java

Here's a comparison table for checked vs. unchecked exceptions:

Criteria	Checked Exceptions	Unchecked Exceptions
Definition	Checked at compile-time.	Checked at runtime.
Subclass of	All the subclasses of java.lang.Exception are checked exceptions.	All the subclasses of java.lang.RunTimeException are unchecked exceptions.
Handling Requirement	A checked exception must be handled either by re-throwing or with a try-catch block.	An unchecked exception isn’t required to be handled.
Purpose	Anticipate and recover from abnormal situations that are external to the application.	Result from programming mistakes, incorrect assumptions, or logical errors in the code.
Examples	FileNotFoundException, IOException, ClassNotFoundException.	NullPointerException, ArrayIndexOutOfBoundsException, ArithmeticException.
Recovery Strategy	Expected to provide recovery mechanisms.	Typically fix the code rather than attempting runtime recovery.