Object sorting in Java using Comparable & Comparator Interface and Inner class
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
*
* Java program to test Object sorting in Java. This Java program
* test Comparable and Comparator implementation provided by Order
* class by sorting list of Order object in ascending and descending order.
* Both in natural order using Comparable and custom Order using Comparator in Java
*
*/
public class ObjectSortingExample {
public static void main(String args[]) {
//Creating Order object to demonstrate Sorting of Object in Java
Order ord1 = new Order(101,6000, "Sony");
Order ord2 = new Order(102,2000, "Hitachi");
Order ord3 = new Order(103,4000, "Philips");
//putting Objects into Collection to sort
List orders = new ArrayList();
orders.add(ord3);
orders.add(ord1);
orders.add(ord2);
//printing unsorted collection
System.out.println("Unsorted Collection : " + orders);
//Sorting Order Object on natural order - ascending
Collections.sort(orders);
//printing sorted collection
System.out.println("List of Order object sorted in natural order : " + orders);
// Sorting object in descending order in Java
Collections.sort(orders, Collections.reverseOrder());
System.out.println("List of object sorted in descending order : " + orders);
//Sorting object using Comparator in Java
Collections.sort(orders, new Order.OrderByAmount());
System.out.println("List of Order object sorted using Comparator - amount : " + orders);
// Comparator sorting Example - Sorting based on customer
Collections.sort(orders, new Order.OrderByCustomer());
System.out.println("Collection of Orders sorted using Comparator - by customer : " + orders);
}
}
/*
* Order class is a domain object which implements
* Comparable interface to provide sorting on natural order.
* Order also provides couple of custom Comparators to
* sort object based upon amount and customer
*/
class Order implements Comparable {
private int orderId;
private int amount;
private String customer;
/*
* Comparator implementation to Sort Order object based on Amount
*/
public static class OrderByAmount implements Comparator {
@Override
public int compare(Order o1, Order o2) {
return o1.amount > o2.amount ? 1 : (o1.amount < o2.amount ? -1 : 0);
}
}
/*
* Another implementation or Comparator interface to sort list of Order object
* based upon customer name.
*/
public static class OrderByCustomer implements Comparator {
@Override
public int compare(Order o1, Order o2) {
return o1.customer.compareTo(o2.customer);
}
}
public Order(int orderId, int amount, String customer) {
this.orderId = orderId;
this.amount = amount;
this.customer = customer;
}
public int getAmount() {return amount; }
public void setAmount(int amount) {this.amount = amount;}
public String getCustomer() {return customer;}
public void setCustomer(String customer) {this.customer = customer;}
public int getOrderId() {return orderId;}
public void setOrderId(int orderId) {this.orderId = orderId;}
/*
* Sorting on orderId is natural sorting for Order.
*/
@Override
public int compareTo(Order o) {
return this.orderId > o.orderId ? 1 : (this.orderId < o.orderId ? -1 : 0);
}
/*
* implementing toString method to print orderId of Order
*/
@Override
public String toString(){
return String.valueOf(orderId);
}
}
