Java 8 provides different utility api methods to help us sort the streams better.
If your list is a list of Integers(or Double, Long, String etc.,) then you can simply sort the list with default comparators provided by java.
List<Integer> integerList = Arrays.asList(1, 4, 3, 4, 5);
Creating comparator on fly:
integerList.stream().sorted((i1, i2) -> i1.compareTo(i2)).forEach(System.out::println);
With default comparator provided by java 8 when no argument passed to sorted():
integerList.stream().sorted().forEach(System.out::println); //Natural order
If you want to sort the same list in reverse order:
integerList.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println); // Reverse Order
If your list is a list of user defined objects, then:
List<Person> personList = Arrays.asList(new Person(1000, "First", 25, 30000), new Person(2000, "Second", 30, 45000), new Person(3000, "Third", 35, 25000));
Creating comparator on fly:
personList.stream().sorted((p1, p2) -> ((Long)p1.getPersonId()).compareTo(p2.getPersonId())) .forEach(person -> System.out.println(person.getName()));
Using Comparator.comparingLong() method(We have comparingDouble(), comparingInt() methods too):
personList.stream().sorted(Comparator.comparingLong(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
Using Comparator.comparing() method(Generic method which compares based on the getter method provided):
personList.stream().sorted(Comparator.comparing(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
We can do chaining too using thenComparing() method:
personList.stream().sorted(Comparator.comparing(Person::getPersonId).thenComparing(Person::getAge)).forEach(person -> System.out.println(person.getName())); //Sorting by person id and then by age.
Person class
public class Person { private long personId; private String name; private int age; private double salary; public long getPersonId() { return personId; } public void setPersonId(long personId) { this.personId = personId; } public Person(long personId, String name, int age, double salary) { this.personId = personId; this.name = name; this.age = age; this.salary = salary; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public double getSalary() { return salary; } public void setSalary(double salary) { this.salary = salary; } }
