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;
}
}
