User Defined Exception in Java

User Defined Exception in Java

Introduction
In Java, exceptions are used to handle error conditions and exceptional situations that may occur during program execution. While Java provides a set of built-in exceptions, sometimes it is necessary to define custom exceptions to handle specific scenarios in an application. Creating a user-defined exception allows developers to design error-handling mechanisms tailored to their application's requirements.

Creating a User-Defined Exception
To create a user-defined exception in Java, you need to define a new class that extends one of the existing exception classes provided by Java (usually Exception or one of its subclasses like RuntimeException).

Example: CustomCheckedException

java
// CustomCheckedException.java
public class CustomCheckedException extends Exception {
    public CustomCheckedException(String message) {
        super(message);
    }
}

Explanation:

• We define a new class CustomCheckedException that extends the Exception class, which makes it a checked exception. Checked exceptions are required to be caught or declared using the throws keyword.
• The constructor of the CustomCheckedException class takes a String parameter message which represents the error message associated with the exception.
• We call the superclass constructor super(message) to set the error message using the message parameter.

Example: CustomUncheckedException

java
// CustomUncheckedException.java
public class CustomUncheckedException extends RuntimeException {
    public CustomUncheckedException(String message) {
        super(message);
    }
}

Explanation:

• We define a new class CustomUncheckedException that extends the RuntimeException class, making it an unchecked exception. Unchecked exceptions are not required to be caught or declared.
• The constructor of the CustomUncheckedException class also takes a String parameter message to set the error message, similar to the checked exception example.

Using the Custom Exceptions

Now, let's see how to use the custom exceptions in a Java program.

Example: Using Custom Exceptions

java
public class Example {
    public static void main(String[] args) {
        try {
            // Some code that may throw the custom exception
            throwCustomCheckedException();
            // Or throwCustomUncheckedException();
        } catch (CustomCheckedException e) {
            System.out.println("Caught CustomCheckedException: " + e.getMessage());
        } catch (CustomUncheckedException e) {
            System.out.println("Caught CustomUncheckedException: " + e.getMessage());
        }
    }

    public static void throwCustomCheckedException() throws CustomCheckedException {
        throw new CustomCheckedException("This is a checked exception example.");
    }

    public static void throwCustomUncheckedException() {
        throw new CustomUncheckedException("This is an unchecked exception example.");
    }
}

Explanation:

• In the main method, we try to execute the throwCustomCheckedException() or throwCustomUncheckedException() methods, both of which can throw custom exceptions.
• We catch the custom exceptions separately using catch blocks, and then print the error message using e.getMessage().

Conclusion
Creating user-defined exceptions in Java provides flexibility in handling application-specific errors. By extending existing exception classes, developers can tailor the exception hierarchy to better manage error scenarios in their Java programs. Remember to use checked exceptions for recoverable errors and unchecked exceptions for unexpected and fatal errors.