Java IllegalArgumentException

Introduction

IllegalArgumentException in Java is a runtime exception that occurs when a method receives an argument that is not valid. It helps ensure that methods are used with proper inputs.

Table of Contents

1. What is IllegalArgumentException?
2. Common Causes
3. Handling IllegalArgumentException
4. Examples of IllegalArgumentException
5. Conclusion

1. What is IllegalArgumentException?

IllegalArgumentException is thrown to indicate that a method has been passed an inappropriate or invalid argument. It signals that the method’s contract has been violated.

2. Common Causes

• Passing null to methods that do not accept null.
• Providing arguments out of the acceptable range.
• Passing incompatible types.

3. Handling IllegalArgumentException

To handle IllegalArgumentException:

• Use input validation before method calls.
• Implement try-catch blocks where necessary.
• Document method requirements clearly.

4. Examples of IllegalArgumentException

Example 1: Validating Method Arguments

This example demonstrates how to validate arguments to prevent IllegalArgumentException.

public class ArgumentValidationExample { public static int divide(int a, int b) { if (b == 0) { throw new IllegalArgumentException("Divisor cannot be zero."); } return a / b; } public static void main(String[] args) { try { System.out.println("Result: " + divide(10, 2)); System.out.println("Result: " + divide(10, 0)); // Throws IllegalArgumentException } catch (IllegalArgumentException e) { System.out.println("Error: " + e.getMessage()); } } } 

Output:

Result: 5 Error: Divisor cannot be zero. 

Example 2: Handling IllegalArgumentException

Here, we handle IllegalArgumentException when an invalid argument is passed.

public class InvalidArgumentExample { public static void setAge(int age) { if (age < 0 || age > 150) { throw new IllegalArgumentException("Age must be between 0 and 150."); } System.out.println("Age set to: " + age); } public static void main(String[] args) { try { setAge(25); setAge(-5); // Throws IllegalArgumentException } catch (IllegalArgumentException e) { System.out.println("Error: " + e.getMessage()); } } } 

Output:

Age set to: 25 Error: Age must be between 0 and 150. 

Conclusion

IllegalArgumentException in Java is crucial for maintaining method integrity by ensuring that arguments passed to methods are valid. By properly validating inputs and handling exceptions, you can prevent errors and ensure that methods function correctly.