Types of Exceptions in Java

In Java, exceptions are events that disrupt the normal flow of a program. They are classified into different types based on when they occur and how they should be handled.

Checked Exceptions (Compile-Time Exceptions)

• Checked exceptions are verified by the compiler at compile-time.
• Must be handled using try-catch or throws, otherwise the program won’t compile.
• Usually occur due to external factors like files, network, or database errors.

Common Examples:

Exception	Cause
IOException	File read/write errors
SQLException	Database access issues
FileNotFoundException	File does not exist
ClassNotFoundException	Class not found
InterruptedException	Thread interruption

Example:

import java.io.*;

public class CheckedExample {
    public static void main(String[] args) throws IOException {
        FileReader fr = new FileReader("data.txt"); // Checked Exception
    }
}

---

Unchecked Exceptions (Runtime Exceptions)

• Occur during program execution; not checked at compile-time.
• Usually caused by programmer mistakes, invalid logic, or improper use of objects.

Common Examples:

Exception	Cause
ArithmeticException	Divide by zero
NullPointerException	Using null object
ArrayIndexOutOfBoundsException	Invalid array index
NumberFormatException	Invalid string-to-number conversion
ClassCastException	Wrong type casting

Example:

public class UncheckedExample {
    public static void main(String[] args) {
        int result = 10 / 0; // Runtime Exception
    }
}

---

Errors (Not Exceptions)

• Errors are serious problems in JVM that are generally non-recoverable.
• Should not be handled by the program; usually indicate system failure.

Common Examples:

Error	Cause
OutOfMemoryError	JVM heap memory full
StackOverflowError	Infinite recursion
VirtualMachineError	JVM internal failure

Example:

public class ErrorExample {
    public static void recursive() {
        recursive(); // Infinite recursion
    }
    public static void main(String[] args) {
        recursive(); // StackOverflowError
    }
}

---

Exception Hierarchy

Throwable
│
├── Exception (Recoverable)
│     ├── Checked Exception
│     └── Unchecked Exception (RuntimeException)
│
└── Error (Non-Recoverable)

---

Comparison Table

Type	Checked By Compiler?	Occurrence	Examples	Can Handle?
Checked	Yes	Compile-time	IOException, SQLException	Yes
Unchecked	No	Runtime	NullPointerException, ArithmeticException	Yes
Error	No	JVM failure	OutOfMemoryError, StackOverflowError	No

Points to Remember:

• Checked exceptions are predictable and must be handled.
• Unchecked exceptions are mostly due to logical errors.
• Errors indicate serious JVM problems that cannot be recovered.
• Exception handling ensures program stability and prevents crashes.