Exception Handling

import java.io.*;
import java.util.*;

public class ExceptionHandling {
    // Checked exception — must declare or catch it
    public static String readFile(String path) throws IOException {
        StringBuilder sb = new StringBuilder();
        try (BufferedReader reader = new BufferedReader(new FileReader(path))) {
            String line;
            while ((line = reader.readLine()) != null) {
                sb.append(line).append("\n");
            }
        }
        return sb.toString();  // auto-closes reader (try-with-resources)
    }

    // Custom exception
    static class InsufficientFundsException extends RuntimeException {
        private final double amount;
        private final double balance;

        InsufficientFundsException(double amount, double balance) {
            super(String.format("Cannot withdraw %.2f, balance is %.2f", amount, balance));
            this.amount = amount;
            this.balance = balance;
        }

        public double getAmount() { return amount; }
        public double getBalance() { return balance; }
    }

    public static void main(String[] args) {
        // try-catch-finally
        try {
            String content = readFile("data.txt");
            System.out.println(content);
        } catch (FileNotFoundException e) {
            System.err.println("File not found: " + e.getMessage());
        } catch (IOException e) {
            System.err.println("IO error: " + e.getMessage());
        } finally {
            System.out.println("Always runs");
        }

        // Multi-catch (Java 7+)
        try {
            int[] arr = {1, 2, 3};
            int n = Integer.parseInt("abc");
            System.out.println(arr[n]);
        } catch (NumberFormatException | ArrayIndexOutOfBoundsException e) {
            System.err.println("Error: " + e.getMessage());
        }
    }
}