Exception Handling in Java

- July 18, 2025

Chapter 9: Exception Handling in Java

In Java, exception handling is a powerful mechanism to handle runtime errors, allowing the normal flow of the program to continue. Without proper exception handling, errors can lead to unexpected termination of the program.

📌 What is an Exception?

An exception is an event that disrupts the normal flow of a program’s execution. It is an object which is thrown at runtime.

Common Exception Types:

ArithmeticException – Divide by zero
NullPointerException – Accessing object with null reference
ArrayIndexOutOfBoundsException – Invalid index access
NumberFormatException – Invalid number parsing

🧪 Java Exception Hierarchy

All exceptions are subclasses of Throwable:

Throwable
- Error
- Exception
  - RuntimeException

🔧 Java Exception Handling Keywords

try – Code that might throw an exception
catch – Code to handle the exception
finally – Code that executes regardless of an exception
throw – Used to explicitly throw an exception
throws – Declares the exceptions a method might throw

💡 Example: try-catch

public class Demo {
  public static void main(String[] args) {
    try {
      int result = 10 / 0;
    } catch (ArithmeticException e) {
      System.out.println("Error: " + e.getMessage());
    }
  }
}

🧹 finally Block

The finally block executes whether an exception is handled or not. It is often used to close resources like files or database connections.

Example:

try {
  int data = 50 / 0;
} catch (ArithmeticException e) {
  System.out.println("Exception caught");
} finally {
  System.out.println("finally block is always executed");
}

🎯 throw Keyword

The throw keyword is used to throw an exception explicitly.

throw new ArithmeticException("Divide by zero not allowed");

🧾 throws Keyword

throws is used to declare exceptions in the method signature.

public void readFile() throws IOException {
  // file operations
}

🧰 Creating Custom Exceptions

We can create our own exception by extending Exception class:

class MyException extends Exception {
  MyException(String msg) {
    super(msg);
  }
}

✅ Benefits of Exception Handling

Improves code robustness
Enhances program readability
Prevents abrupt termination
Helps debugging and maintenance

📘 Chapter Summary

Concept	Description
Exception	Runtime error that disrupts program flow
try-catch	Handle exceptions gracefully
finally	Cleanup block executed always
throw	Used to throw custom exception
throws	Declares exceptions in method

❓ FAQs with Answers

Q1: What is an exception in Java?

A: An exception is a runtime error that disrupts the normal flow of a program.

Q2: What are checked and unchecked exceptions?

A: Checked exceptions are checked at compile time (e.g., IOException). Unchecked exceptions occur at runtime (e.g., NullPointerException).

Q3: What is the use of finally block?

A: To ensure execution of important cleanup code, even if an exception occurs.

Q4: What’s the difference between throw and throws?

A: throw is used to throw an exception, throws is used to declare possible exceptions.

Q5: Can a method have multiple catch blocks?

A: Yes, to handle different types of exceptions separately.

Q6: What is a custom exception?

A: A user-defined class extending Exception to represent specific errors.

Q7: What happens if an exception is not caught?

A: Program terminates and displays the exception stack trace.

Q8: Can we have try block without catch?

A: Yes, only if a finally block is present.

Q9: How to catch multiple exceptions in one block?

A: From Java 7 onward, use pipe symbol (|):

catch (IOException | SQLException e) {}

Q10: Is it good to catch Exception class directly?

A: No, it’s not recommended as it hides specific exception causes.

Search This Blog

FutureAIMinds.com