Common Exceptions and their Causes

Java provides a robust exception-handling mechanism, and understanding common exceptions and their typical causes is essential for writing reliable applications. Below are some of the most frequently encountered exceptions in Java along with what typically causes them:

1. NullPointerException

• Cause: Accessing a method or field of an object that is null.
• Example Scenario: Calling length() on a null string or trying to access elements in a null array.

2. ArrayIndexOutOfBoundsException

• Cause: Trying to access an array index that is outside its valid range (less than 0 or greater than length - 1).
• Example Scenario: Accessing arr[10] when the array length is 5.

3. ClassCastException

• Cause: Improper casting between incompatible types.
• Example Scenario: Casting an Object to String when the actual object is an Integer.

4. NumberFormatException

• Cause: Trying to convert a string into a numeric type when the string doesn’t have a valid format.
• Example Scenario: Parsing "abc" using Integer.parseInt().

5. ArithmeticException

• Cause: Performing illegal arithmetic operations, such as dividing by zero.
• Example Scenario: Executing int result = 10 / 0.

6. IllegalArgumentException

• Cause: Passing illegal or inappropriate arguments to a method.
• Example Scenario: Providing a negative value for a method that expects only positive values.

7. IllegalStateException

• Cause: Calling a method at an inappropriate or illegal time.
• Example Scenario: Modifying a collection while iterating over it with an iterator.

8. FileNotFoundException

• Cause: Trying to open a file that does not exist.
• Example Scenario: Attempting to read a file from a non-existent path.

9. IOException

• Cause: Issues during input or output operations, typically when reading from or writing to files.
• Example Scenario: Reading from a file that suddenly becomes inaccessible.

10. SQLException

• Cause: Problems encountered while interacting with a database using JDBC.
• Example Scenario: Executing malformed SQL queries or accessing a closed connection.

11. InterruptedException

• Cause: A thread is interrupted while it is waiting, sleeping, or otherwise occupied.
• Example Scenario: Calling Thread.sleep() and the thread is interrupted.

12. NoSuchElementException

• Cause: Trying to access an element that doesn’t exist, typically in iterators or scanners.
• Example Scenario: Calling next() on an iterator with no more elements.

13. UnsupportedOperationException

• Cause: Calling an operation that isn’t supported by the object.
• Example Scenario: Trying to modify an unmodifiable collection.

These exceptions are part of everyday Java development, and knowing their causes can help prevent and handle them effectively. Proper exception handling, defensive programming (like null checks and input validation), and thorough testing are key strategies to reduce the impact of these exceptions in real-world applications.