Static Method for Utility Class: String Reversal

This example demonstrates a utility class with a static method for reversing a string. The StringUtil class provides a reusable function that can be called directly on the class without creating an instance.

Code Snippet

The StringUtil class is designed as a utility class. It has a private constructor to prevent instantiation. The reverseString() method is a static method that takes a string as input and returns the reversed string. The method handles null and empty strings gracefully. The main() method demonstrates how to call the static method directly on the StringUtil class.

public class StringUtil {

    // Private constructor to prevent instantiation
    private StringUtil() {
        // Utility class, should not be instantiated
    }

    public static String reverseString(String input) {
        if (input == null || input.isEmpty()) {
            return input;
        }
        return new StringBuilder(input).reverse().toString();
    }

    public static void main(String[] args) {
        String str = "hello";
        String reversed = StringUtil.reverseString(str);
        System.out.println("Original string: " + str);
        System.out.println("Reversed string: " + reversed);
    }
}

Concepts Behind the Snippet

Static methods are often used for utility functions that don't depend on the state of any particular object. They are called directly on the class using the class name, e.g., ClassName.staticMethod(). A private constructor prevents creating objects of this class.

Real-Life Use Case

Utility classes with static methods are commonly used for tasks like string manipulation, date formatting, mathematical calculations, or data validation. They provide reusable functionality that can be easily accessed throughout the application.

Best Practices

• Keep utility classes focused on a specific set of related functions.
• Make the constructor private to prevent instantiation of utility classes.
• Ensure that static methods are thread-safe if they are used in a multi-threaded environment.

Interview Tip

Be able to explain the purpose of utility classes and when it's appropriate to use them. Understand the difference between static and instance methods and when to use each. Be prepared to discuss the importance of thread safety when using static methods in multi-threaded applications.

When to Use Them

Use static methods in utility classes when you need reusable functions that don't depend on the state of any particular object. This promotes code reuse and avoids unnecessary object creation.

Memory Footprint

Since utility classes are not instantiated (due to the private constructor), they don't contribute to the memory footprint in terms of object instances. The static methods and any static variables they use are loaded into memory when the class is loaded.

Alternatives

• Instance Methods: If the utility function depends on the state of an object, it should be an instance method instead of a static method.
• Functional Interfaces (Java 8+): For simple utility functions, consider using functional interfaces and lambda expressions.

Pros

• Improved code reusability.
• Avoids unnecessary object creation.
• Easy to access utility functions throughout the application.

Cons

• Can make code harder to test if static methods have dependencies that are difficult to mock.
• Overuse of static methods can lead to tightly coupled code.