Lambda expression is a new feature that created in Java 8. It provides a clean and concise way to implement one method interface aka @FunctionalInterface. You are maybe familiar on using Runnable or Comparator class. Implementing these classes, requires you to create a new class or anonymous class. Luckily lambda is existed thus removing the verbosity of the Java language.

Say we want to sort a list of names. We can use Collections.sort() method and implement an anonymous class of Comparator.

List<String> names = Arrays.asList("Jerome", "Steve", "Cathy", "Lara");

Collections.sort(names, new Comparator<String>() {
    @Override
    public int compare(String a, String b) {
        return b.compareTo(a);
    }
});

We can shorten the code above using lambda expression.

Collections.sort(names, (String a, String b) -> {
    return b.compareTo(a);
});

Heck, we can even make it shorter. If it is just one liner method, we can omit the braces and return keyword.

Collections.sort(names, (a, b) -> b.compareTo(a));

Sweet! Lambda expression not only make our code readable but also removes the noise from it, giving us more focus in the behavior part of our code.