Java Try, Catch & Finally: Handling Exceptions & Multi-Catch Blocks

The try-catch-finally construct is Java's primary mechanism for trapping runtime exceptions and executing mandatory resource clean-up routines.

1. Basic Try-Catch Block

Statements that might generate a runtime error are enclosed within a try block. If an error occurs, JVM skips the remaining try block code and transfers control to the matching catch block:

public class TryCatchDemo {
    public static void main(String[] args) {
        System.out.println("Starting computation...");

        try {
            int a = 50;
            int b = 0;
            int result = a / b; // Throws ArithmeticException (/ by zero)
            System.out.println("Result: " + result); // Skipped!
        } catch (ArithmeticException e) {
            System.err.println("Caught Error: Cannot divide a number by zero! Details: " + e.getMessage());
        }

        System.out.println("Program resumed smoothly after catch block!");
    }
}

2. Ordering Multiple Catch Blocks (Specific to General)

You can chain multiple catch blocks to handle different failure modes distinctly. Always order from subclass to superclass:

try {
    int[] arr = new int[5];
    arr[10] = 50; // Triggers ArrayIndexOutOfBoundsException
} catch (ArithmeticException e) {
    System.out.println("Mathematical error occurred.");
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Array index out of range!");
} catch (Exception e) {
    // Catch-all fallback: Must be at the BOTTOM!
    System.out.println("General exception caught: " + e.getMessage());
}

3. Modern Java 7 Multi-Catch Block (Pipe Operator)

try {
    // Operations that might throw multiple unrelated exceptions
    processDatabaseRecord();
} catch (SQLException | IOException e) {
    // Multi-catch: e is implicitly final!
    System.err.println("Database or I/O failure: " + e.getMessage());
}

4. The Guaranteed finally Block

The finally block executes 100% of the time, ensuring database connections, file handles, and network sockets are closed:

try {
    System.out.println("Inside try block");
    return; // Even with early return, finally STILL EXECUTES!
} finally {
    System.out.println("Inside finally block: Cleanup finished!");
}