The type of exception tells you what kind of problem happened, such as a missing file or a calculation error. Java organizes exceptions into different categories, so you can handle each situation in the right way. Learning about these types helps you write safer and more reliable code.

Main Categories of Exceptions in Java

Java exceptions are divided into two main categories: checked exceptions and unchecked exceptions. Understanding the difference between these categories is essential for writing reliable Java programs.

Checked Exceptions

Checked exceptions are exceptions that the Java compiler requires you to handle. You will learn how to handle exceptions later.

Checked exceptions are typically used for conditions that a reasonable program should anticipate and recover from, such as file input/output errors or database connection issues.

• The compiler checks at compile time that you have handled these exceptions;
• Examples include IOException, SQLException, and ClassNotFoundException;
• You must handle or declare checked exceptions, or your code will not compile.

Unchecked Exceptions

Unchecked exceptions are exceptions that the compiler does not require you to handle explicitly. These exceptions usually represent programming errors, such as logic mistakes or improper use of an API. Unchecked exceptions are subclasses of RuntimeException and its subclasses.

• The compiler does not check whether you handle these exceptions;
• Examples include NullPointerException, ArrayIndexOutOfBoundsException, and IllegalArgumentException;
• You are not required to catch or declare unchecked exceptions, but you can handle them if needed.

Summary:

• Checked exceptions must be handled or declared;
• Unchecked exceptions do not require explicit handling, but can cause your program to terminate if not managed properly.

Common Checked and Unchecked Exception Types

Understanding the difference between checked and unchecked exceptions is essential for effective error handling in Java. Here are some widely encountered examples:

Checked Exceptions

• IOException: indicates an input or output operation failure, such as problems reading from a file or network connection;
• SQLException: signals issues related to database access or SQL queries, such as invalid queries or connection failures.

Unchecked Exceptions

• NullPointerException: occurs when you try to use an object reference that has not been initialized (is null);
• ArithmeticException: arises during illegal arithmetic operations, such as dividing a number by zero.

You must handle checked exceptions explicitly in your code, while unchecked exceptions can occur at runtime and may not need to be declared or caught.