What is an Exception in Java?

An exception in Java is an unexpected event that occurs during the execution of a program and interrupts the normal flow of instructions. It is not a compile-time error, it happens at runtime.

Simple Definition

An exception is a runtime problem that stops program execution unless handled properly.

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Why Exceptions Occur?

Exceptions occur due to invalid operations, such as:

• Dividing a number by zero
• Accessing an array index out of range
• Opening a file that doesn’t exist
• Passing null where an object is required
• Type conversion errors
• Network or database failure

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Example: Without Exception Handling

public class Example {
    public static void main(String[] args) {
        int a = 10;
        int b = 0;
        int result = a / b;   // Exception occurs here
        System.out.println(result);
    }
}

Output:

Exception in thread "main" java.lang.ArithmeticException: / by zero

Program crashes and stops executing.

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How Java Handles Exceptions?

When an exception occurs:

1. Java creates an Exception object
2. Passes (throws) it to the JVM
3. JVM looks for a matching catch block
4. If not found → program terminates abnormally

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Exception vs Error

Feature	Exception	Error
Type	Recoverable	Non-recoverable
Examples	ArithmeticException, NullPointerException	OutOfMemoryError, StackOverflowError
Programmer Can Handle?	YES	NO
Package	java.lang.Exception	java.lang.Error

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Exception Hierarchy

Throwable
│
├── Exception  → can be handled
│     ├── RuntimeException
│     └── IOException, SQLException etc.
│
└── Error      → cannot be handled

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Real-Life Analogy

If your laptop suddenly shuts down while working → this interruption is similar to a Java exception.

If your laptop’s motherboard burns → it’s like a Java Error → cannot be handled.

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Why Exception Handling is Needed?

• Prevents program crashes
• Displays meaningful error messages
• Allows graceful program recovery
• Helps debugging
• Makes applications more stable & user-friendly