Best Practices for Handling Null Parameters in Java Constructors

What are the best practices for handling null parameters in Java class constructors?

public class SomeClass {
    public SomeClass(Object one, Object two) {
        if (one == null) {
            throw new IllegalArgumentException("one can't be null");
        }
        if (two == null) {
            throw new IllegalArgumentException("two can't be null");
        }
        // Initialization code...
    }
}

Ensuring that parameters passed to constructors are not null is crucial for maintaining class invariants and preventing runtime exceptions in Java applications. In this answer, we discuss best practices for validating constructor parameters and present approaches that enhance code readability and maintainability.

public class SomeClass {
    public SomeClass(Object one, Object two) {
        if (one == null) {
            throw new IllegalArgumentException("one can't be null");
        }
        if (two == null) {
            throw new IllegalArgumentException("two can't be null");
        }
        // Initialization code...
    }
}

Causes

• Passing null values unintentionally due to incorrect object initialization.
• Failure to validate constructor arguments can lead to NullPointerExceptions during runtime.

Solutions

• Use conditioned checks at the beginning of the constructor to validate parameters.
• Consider alternative approaches like using builder patterns or static factory methods that enforce non-null parameters.
• Utilize Java annotations such as @NonNull from libraries like Lombok or JSR 305 to indicate expected non-null parameters.

Mistake: Assuming all parameters will never be null without validation.

Solution: Always validate constructor parameters to ensure they meet expected non-null conditions.

Mistake: Throwing generic exceptions without specific details.

Solution: Use detailed and descriptive exceptions messages to clarify which parameter is null.

Mistake: Overcomplicating constructors by delegating checks to setter methods.

Solution: Keep constructor logic straightforward and handle parameter validation directly within the constructor.