How to Perform Exception Handling in Java?

The following code example demonstrates How to Perform Exception Handling in Java.

try-catch

Basically, we use this block to catch and handle exceptions.

public class TryCatchExample {
    public static void main(String[] args) {
        try {
            int result = divide(10, 0); // This will throw an ArithmeticException
            System.out.println("Result: " + result);
        } catch (ArithmeticException e) {
            System.out.println("Exception caught: " + e.getMessage());
        }
    }

    public static int divide(int dividend, int divisor) {
        return dividend / divisor;
    }
}

In this example, we attempt to divide by zero, which results in an ArithmeticException. Indeed, we catch this exception in the catch block and handle it.

throw

We use the throw keyword to manually throw an exception. For example.

public class ThrowExample {
    public static void main(String[] args) {
        try {
            validateAge(15); // This will throw an IllegalArgumentException
        } catch (IllegalArgumentException e) {
            System.out.println("Exception caught: " + e.getMessage());
        }
    }

    public static void validateAge(int age) {
        if (age < 18) {
            throw new IllegalArgumentException("Age must be 18 or older");
        }
        System.out.println("Age is valid");
    }
}

In this example, we manually throw an IllegalArgumentException if the age is less than 18.

throws

We use the throws keyword in method signatures to indicate that a method may throw certain exceptions. For example.

public class ThrowsExample {
    public static void main(String[] args) {
        try {
            readFile("nonexistent.txt"); // This may throw a FileNotFoundException
        } catch (FileNotFoundException e) {
            System.out.println("Exception caught: " + e.getMessage());
        }
    }

    public static void readFile(String filename) throws FileNotFoundException {
        // Code to read a file (may throw FileNotFoundException)
        // ...
        throw new FileNotFoundException("File not found");
    }
}

Here, the readFile method is declared with throws FileNotFoundException in its signature, indicating that it may throw this exception.

finally

Similarly, we use the finally keyword to define a block of code that will be executed regardless of whether an exception is thrown or not. For example.

public class FinallyExample {
    public static void main(String[] args) {
        try {
            int result = divide(10, 2); // This will not throw an exception
            System.out.println("Result: " + result);
        } catch (ArithmeticException e) {
            System.out.println("Exception caught: " + e.getMessage());
        } finally {
            System.out.println("Finally block executed");
        }
    }

    public static int divide(int dividend, int divisor) {
        return dividend / divisor;
    }
}

In this example, the finally block will always be executed, whether or not an exception occurs.

To summarize, these examples illustrate the use of try, catch, throw, throws, and finally in Java for exception handling.

try-catch

throw

throws

finally

Further Reading