This is example demonstrates that we create a list of person objects and we compare each person's age by using compateTo() method of Comparable Interface. In short, we are sorting persons by age in ascending order.
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Sort User-Defined Objects in Ascending Order in Java
public class Person implements Comparable < Person > { private int id; private String name; private int age; public Person(int id, String name, int age) { this.id = id; this.name = name; this.age = age; } public int getId() { return id; } public void setId(int id) { this.id = id; } 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; } @Override public String toString() { return this.name; } @Override public int compareTo(Person otherPerson) { return (this.getAge() - otherPerson.getAge()); } }Note that Person class implements Comparable interface and provides compareTo() method implementation.
Here is code to test and sort person objects:
import java.util.ArrayList; import java.util.Collections; import java.util.List; public class PersonSorterInASC { public static void main(String[] args) { sortUserDefinedObjectsInAsc(); } private static void sortUserDefinedObjectsInAsc() { List < Person > persons = new ArrayList < Person > (); Person person1 = new Person(59, "John", 40); Person person12 = new Person(67, "Roger", 25); Person person13 = new Person(45, "Steven", 30); persons.add(person1); persons.add(person12); persons.add(person13); System.out.println("Before Sorting : " + persons); Collections.sort(persons); System.out.println("After Sorting : " + persons); } }
Output
Before Sorting : [John, Roger, Steven]
After Sorting : [Roger, Steven, John]
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