Java Notes

EXCEPTION HANDLING IN JAVA


💥 What is an Exception?
An exception is a problem that occurs during the execution of a program. When
this happens, the program stops working normally and may crash unless we
handle the error properly.

🧠 Think of it like this:
Imagine you're withdrawing money from an ATM. If you enter the wrong PIN,
the transaction fails — but the machine doesn’t crash! It shows you a message
and lets you try again. That’s like exception handling.




🛡️Why Do We Need Exception Handling?
 Prevents the program from crashing.
 Helps in debugging (error messages show what went wrong).
 Makes the program more robust and user-friendly.




🔍 Types of Exceptions in Java
✅ Checked Exceptions

 Java forces you to handle these.
 They are checked at compile-time.
 Examples: IOException, SQLException, FileNotFoundException.

📌 Example:
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, FileReader file = new FileReader("file.txt"); // may throw
FileNotFoundException

You must handle it using try-catch or throws.



❌ Unchecked Exceptions

 Optional to handle.
 They happen at runtime.
 Examples: ArithmeticException, NullPointerException,
ArrayIndexOutOfBoundsException.

📌 Example:
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int a = ; // ArithmeticException




🧵 Java Exception Class Hierarchy
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Throwable
├── Error (not recoverable, e.g., memory crash)
└── Exception
├── Checked Exceptions
└── RuntimeException (Unchecked)




⚙️
How Exception Handling Works (with Syntax)
Basic Structure:
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try {
// code that may throw exception
} catch (ExceptionType e) {
// code to handle the exception
} finally {
// code that always runs (optional)