What is Exception Handling in Java?

Exception Handling is a mechanism to handle runtime errors gracefully, preventing abrupt program termination.

1. try-catch Block

public class TryCatchExample {
    public static void main(String[] args) {
        try {
            int[] numbers = {1, 2, 3};
            System.out.println(numbers[5]); // ArrayIndexOutOfBoundsException
            int result = 10 / 0; // ArithmeticException
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Array index error: " + e.getMessage());
        } catch (ArithmeticException e) {
            System.out.println("Math error: " + e.getMessage());
        }
        
        System.out.println("Program continues normally");
    }
}

2. finally Block

Executes whether exception occurs or not (cleanup code).

import java.io.*;

public class FinallyExample {
    public static void main(String[] args) {
        FileReader file = null;
        try {
            file = new FileReader("test.txt");
            System.out.println("File opened");
        } catch (FileNotFoundException e) {
            System.out.println("File not found");
        } finally {
            try {
                if (file != null) {
                    file.close();
                    System.out.println("File closed");
                }
            } catch (IOException e) {
                System.out.println("Error closing file");
            }
        }
    }
}

3. throw Keyword

Manually throw an exception.

class AgeValidator {
    static void validateAge(int age) {
        if (age < 18) {
            throw new IllegalArgumentException("Age must be 18 or above");
        } else {
            System.out.println("Valid age: " + age);
        }
    }
    
    public static void main(String[] args) {
        try {
            validateAge(15);
        } catch (IllegalArgumentException e) {
            System.out.println("Exception caught: " + e.getMessage());
        }
        validateAge(20); // Valid age: 20
    }
}

4. throws Keyword

Declares that a method might throw exceptions.

import java.io.*;

class FileHandler {
    public static void readFile(String filename) throws IOException {
        BufferedReader reader = new BufferedReader(new FileReader(filename));
        String line = reader.readLine();
        System.out.println("First line: " + line);
        reader.close();
    }
    
    public static void main(String[] args) {
        try {
            readFile("nonexistent.txt");
        } catch (IOException e) {
            System.out.println("Handled exception: " + e.getMessage());
        }
    }
}

5. try-with-resources (Java 7+)

Automatically closes resources.

try (BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {
    System.out.println(br.readLine());
} catch (IOException e) {
    e.printStackTrace();
} // br automatically closed

Multi-catch Block (Java 7+)

try {
    // code that can throw multiple exceptions
} catch (IOException | SQLException e) {
    System.out.println("Error: " + e.getMessage());
}

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