Course – LS – All

Get started with Spring and Spring Boot, through the Learn Spring course:


1. Introduction

Java’s versatility is evident in its ability to handle generic Number objects.

In this tutorial, we’ll delve into the nuances of comparing these objects, offering detailed insights and code examples for each strategy.

2. Using doubleValue() Method

Converting both Number objects to their double representation is a foundational technique in Java.

While this approach is intuitive and straightforward, it’s not without its caveats.

When converting numbers to their double form, there’s a potential for precision loss. This is especially true for large floating-point numbers or numbers with many decimal places:

public int compareDouble(Number num1, Number num2) {
    return, num2.doubleValue());

We must be vigilant and consider the implications of this conversion, ensuring that the results remain accurate and reliable.

3. Using compareTo() Method

Java’s wrapper classes are more than just utility classes for primitive types. The abstract class Number doesn’t implement the compareTo() method, but classes like Integer, Double, or BigInteger have a built-in compareTo() method.

Let’s create our custom compareTo() for type-specific comparisons, ensuring both type safety and precision:

// we create a method that compares Integer, but this could also be done for other types e.g. Double, BigInteger
public int compareTo(Integer int1, Integer int2) {
    return int1.compareTo(int2);

However, when working with several different types, we might encounter challenges.

It’s essential to understand the nuances of each wrapper class and how they interact with one another to ensure accurate comparisons.

4. Using BiFunction and Map

Java’s ability to seamlessly integrate functional programming with traditional data structures is remarkable.

Let’s create a dynamic comparison mechanism using BiFunction by mapping each Number subclass to a specific comparison function using maps:

// for this example, we create a function that compares Integer, but this could also be done for other types e.g. Double, BigInteger
Map<Class<? extends Number>, BiFunction<Number, Number, Integer>> comparisonMap
  = Map.ofEntries(entry(Integer.class, (num1, num2) -> ((Integer) num1).compareTo((Integer) num2)));

public int compareUsingMap(Number num1, Number num2) {
    return comparisonMap.get(num1.getClass())
      .apply(num1, num2);

This approach offers both versatility and adaptability, allowing for comparisons across various number types. It’s a testament to Java’s flexibility and its commitment to providing us with powerful tools.

5. Using Proxy and InvocationHandler

Let’s look into Java’s more advanced features, like proxies combined with InvocationHandlers, which offer a world of possibilities.

This strategy allows us to craft dynamic comparators that can adapt on the fly:

public interface NumberComparator {
    int compare(Number num1, Number num2);

NumberComparator proxy = (NumberComparator) Proxy
  .newProxyInstance(NumberComparator.class.getClassLoader(), new Class[] { NumberComparator.class },
  (p, method, args) -> args[0]).doubleValue(), ((Number) args[1]).doubleValue()));

While this approach provides unparalleled flexibility, it also requires a deep understanding of Java’s inner workings. It’s a strategy best suited for those well-versed in Java’s advanced capabilities.

6. Using Reflection

Java’s Reflection API is a powerful tool, but it comes with its own set of challenges. It allows us to introspect and dynamically determine types and invoke methods:

public int compareUsingReflection(Number num1, Number num2) throws Exception {
    Method method = num1.getClass().getMethod("compareTo", num1.getClass());
    return (int) method.invoke(num1, num2);

We must be careful with using Java’s Reflection because not all the Number classes have the compareTo() method implemented, so we might encounter errors, e.g., when using AtomicInteger and AtomicLong.

However, reflection can be performance-intensive and may introduce potential security vulnerabilities. It’s a tool that demands respect and careful usage, ensuring its power is harnessed responsibly.

7. Using Functional Programming

Java’s evolution has seen a significant shift towards functional programming. This paradigm allows us to craft concise and expressive comparisons using transformation functions, predicates, and other functional constructs:

Function<Number, Double> toDouble = Number::doubleValue;
BiPredicate<Number, Number> isEqual = (num1, num2) -> toDouble.apply(num1).equals(toDouble.apply(num2));

void givenNumbers_whenUseIsEqual_thenWillExecuteComparison() {
    assertEquals(true, isEqual.test(5, 5.0));

It’s an approach that promotes cleaner code and offers a more intuitive way to handle number comparisons.

8. Using Dynamic Comparators with Function

Java’s Function interface is a cornerstone of its commitment to functional programming. By using this interface to craft dynamic comparators, we’re equipped with a flexible and type-safe tool:

private boolean someCondition;
Function<Number, ?> dynamicFunction = someCondition ? Number::doubleValue : Number::intValue;
Comparator<Number> dynamicComparator = (num1, num2) -> ((Comparable) dynamicFunction.apply(num1))

void givenNumbers_whenUseDynamicComparator_thenWillExecuteComparison() {
    assertEquals(0,, 5.0));

It’s an approach that showcases Java’s modern capabilities and its dedication to providing cutting-edge tools.

9. Conclusion

The diverse strategies for comparing generic Number objects in Java have unique characteristics and use cases.

Selecting the appropriate method depends on the context and requirements of our application, and a thorough understanding of each strategy is essential for making an informed decision.

As always, the complete code samples for this article can be found over on GitHub.

Course – LS – All

Get started with Spring and Spring Boot, through the Learn Spring course:

res – REST with Spring (eBook) (everywhere)
Comments are open for 30 days after publishing a post. For any issues past this date, use the Contact form on the site.