Java8 lambda comparator Realtime Examples

In this tutorial, we will learn about using comparators with Lamda. Comparators are extensively used in collections to sort objects link users, employees, orders etc.

In Java 8, comparators can be created using lambda expressions or method references.

Example of how to use a lambda expression to create a comparator:

List<UserInfo> usersData = Arrays.asList(
  new UserInfo("Jayaram", 25),
  new UserInfo("javasavvu", 30),
  new UserInfo("test", 20)
);

Collections.sort(usersData, (u1, u2) -> u1.getAge() - u2.getAge());

In the above examples, (u1, u2) -> u1.getAge() - u2.getAge() is used to compare two UserInfo objects based on their age. The Collections.sort method sorts the list of users based on the comparison result provided by the lambda expression.

Here’s another example using a method reference:

List<UserInfo> usersData = Arrays.asList(
  new UserInfo("Jayaram", 25),
  new UserInfo("javasavvu", 30),
  new UserInfo("test", 20)
);

usersData.sort(Comparator.comparing(UserInfo::getAge));

In this example, the method reference UserInfo::getAge is used to create a Comparator that compares two UserInfo objects based on their age. The Comparator.comparing method takes a Function that extracts a Comparable from the objects being compared, and the method reference is used to create a Comparator that sorts the list of people based on their age.

java 8 comparator on multiple fields

Complex sorting using lambda expressions in Java 8 is possible using the Comparator.comparing and Comparator.thenComparing methods. The Comparator.comparing method takes a Function that extracts a Comparable from the objects being compared, and the Comparator.thenComparing method can be used to specify additional sorting criteria in case of ties.

Here’s an example of complex sorting using lambda expressions:

List<Person> people = Arrays.asList(
  new Person("Jayaram", 25, "New York"),
  new Person("Jay", 30, "London"),
  new Person("Ram", 20, "Paris"),
  new Person("Vinay", 25, "Berlin")
);

people.sort(
  Comparator.comparing(Person::getAge)
    .thenComparing(Person::getName)
    .thenComparing(Person::getCity)
);

In this example, the objects in the people list are sorted first by age, then by name, and finally by city. The Comparator.comparing method is used to extract the values to compare, and the Comparator.thenComparing method is used to specify additional sorting criteria.

Java8 String Comparator Examples

List<String> fruits = Arrays.asList("Apple", "Mango", "BlueBerries" "Banana", "Orange", "Papaya");
// Sorted in natural order
List<String> sorted = fruits.stream().sorted(Comparator.naturalOrder()).collect(Collectors.toList());

// Sorted in the reverse of the natural order
sorted = fruits.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());

// Sorted by length
sorted = bonds.stream().sorted(Comparator.comparingInt(String::length)).collect(Collectors.toList());


// Sorted lowercase
sorted = bonds.stream().sorted(Comparator.comparing(String::toLowerCase)).collect(Collectors.toList());

// Sorting by Multiple Fields
sorted = bonds.stream().sorted(Comparator.comparingInt(String::length).thenComparing(Comparator.naturalOrder())).collect(Collectors.toList());