Multiple Ways to Sort a List of Dates in Java 8

Introduction

Sorting dates in Java can be done in various ways, leveraging different features introduced in Java 8. Here, we’ll explore three methods: using lambda expressions, method references, and the Stream API. Let’s dive into each approach with examples.

1. Using Lambda Expressions

Lambda expressions provide a concise way to represent anonymous functions. They are particularly useful for sorting collections.

List<Invoice> list = service.getInvoiceList();
Comparator<Invoice> comparator = (c1, c2) -> Long.valueOf(c1.getCreatedOn().getTime()).compareTo(c2.getCreatedOn().getTime());
Collections.sort(list, comparator);

In this example, we define a comparator using a lambda expression that compares the creation time of invoices.

2. Using Method References

Method references are a shorthand for lambda expressions that only call a single method. They make the code more readable and concise.

List<Invoice> list = service.getInvoiceList();
list.sort(Comparator.comparing(Invoice::getCreatedOn));

Here, we use a method reference to Invoice::getCreatedOn to create a comparator, and then sort the list directly.

3. Using the Stream API

The Stream API offers a functional approach to processing sequences of elements, including sorting.

List<Invoice> sortedList = service.getInvoiceList().stream()
    .sorted(Comparator.comparing(Invoice::getCreatedOn).reversed())
    .collect(Collectors.toList());

In this example, we create a stream from the list of invoices, sort it in reverse order by the creation date, and collect the sorted elements back into a list.

Conclusion

Java 8 provides multiple elegant ways to sort collections, each suited to different coding styles and requirements. Whether you prefer the directness of lambda expressions, the readability of method references, or the power of the Stream API, Java 8 has you covered.

These examples show how flexible and powerful Java 8’s new features are for common tasks like sorting. Choose the approach that best fits your coding style and project needs. Happy coding!