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Java Comparator Example

Submitted by Andr on Tue, 10/26/2010 - 20:12

Java Examples

package examples;
 
/*
Java Comparator example.
This Java Comparator example describes how java.util.Comparator
interface is implemented to compare Java custom class objects.
 
This Java Comparator is passed to Collection's sorting method
(for example Collections.sort method) to perform sorting of Java custom
class objects.
 
*/
 
import java.util.*;
 
/*
java.util.Comparator interface declares two methods,
1) public int compare(Object object1, Object object2) and
2) boolean equals(Object object)
*/
 
/*
We will compare objects of the Employee class using custom comparators
on the basis of employee age and name.
*/
 
class Employee{
    
    private int age;    
    private String name;
    
    public void setAge(int age){
        this.age=age;    
    }
    
    public int getAge(){
        return this.age;    
    }
    
    public void setName(String name){
        this.name=name;    
    }
    
    public String getName(){    
        return this.name;    
    }
}
 
/*
User defined Java comparator.
To create custom java comparator, implement Comparator interface and
define compare method.
 
The below given comparator compares employees on the basis of their age.
*/
 
class AgeComparator implements Comparator{
    
    public int compare(Object emp1, Object emp2){
    
        /*
         * parameter are of type Object, so we have to downcast it
         * to Employee objects
         */
       
        int emp1Age = ((Employee)emp1).getAge();        
        int emp2Age = ((Employee)emp2).getAge();
       
        if(emp1Age > emp2Age)
            return 1;
        else if(emp1Age < emp2Age)
            return -1;
        else
            return 0;    
    }
    
}
 
/*
The below given comparator compares employees on the basis of their name.
*/
 
class NameComparator implements Comparator{
 
    public int compare(Object emp1, Object emp2){    
 
        //parameter are of type Object, so we have to downcast it to Employee objects
       
        String emp1Name = ((Employee)emp1).getName();        
        String emp2Name = ((Employee)emp2).getName();
       
        //uses compareTo method of String class to compare names of the employee
        return emp1Name.compareTo(emp2Name);
    
    }
 
}
 
/*
This Java comparator example compares employees on the basis of
their age and name and sort them in that order.
*/
 
public class JavaComparatorExample{
    
    public static void main(String args[]){
       
        //Employee array which will hold employees
        Employee employee[] = new Employee[2];
       
        //set different attributes of the individual employee.
        employee[0] = new Employee();
        employee[0].setAge(40);
        employee[0].setName("Joe");
       
        employee[1] = new Employee();
        employee[1].setAge(20);
        employee[1].setName("Mark");
       
        System.out.println("Order of employee before sorting is");
        //print array as is.
        for(int i=0; i < employee.length; i++){
            System.out.println( "Employee " + (i+1) + " name :: " + employee[i].getName() + ", Age :: " + employee[i].getAge());
        }
       
        /*
        Sort method of the Arrays class sorts the given array.        
        Signature of the sort method is,        
        static void sort(Object[] object, Comparator comparator)
       
        IMPORTANT: All methods defined by Arrays class are static. Arrays class        
        serves as a utility class.
        */
       
        //Sorting array on the basis of employee age by passing AgeComparator
        Arrays.sort(employee, new AgeComparator());
        System.out.println("\n\nOrder of employee after sorting by employee age is");
       
        for(int i=0; i < employee.length; i++){
            System.out.println( "Employee " + (i+1) + " name :: " + employee[i].getName() + ", Age :: " + employee[i].getAge());
        }
       
        //Sorting array on the basis of employee Name by passing NameComparator
        Arrays.sort(employee, new NameComparator());
       
        System.out.println("\n\nOrder of employee after sorting by employee name is");    
        for(int i=0; i < employee.length; i++){
            System.out.println( "Employee " + (i+1) + " name :: " + employee[i].getName() + ", Age :: " + employee[i].getAge());
        }
    
    }
 
}
 
/*
OUTPUT of the above given Java Comparable Example would be :
Order of employee before sorting is
Employee 1 name :: Joe, Age :: 40
Employee 2 name :: Mark, Age :: 20
Order of employee after sorting by employee age is
Employee 1 name :: Mark, Age :: 20
Employee 2 name :: Joe, Age :: 40
Order of employee after sorting by employee name is
Employee 1 name :: Joe, Age :: 40
Employee 2 name :: Mark, Age :: 20
*/

Andr's blog

Cool example.

Submitted by Anonymous on Mon, 11/29/2010 - 11:14.

Cool example.

Thanks for your explanation

Submitted by Anonymous on Fri, 02/11/2011 - 14:39.

Thanks for your explanation about Comparator.. I can understand.

very good explanation

Submitted by Anonymous on Wed, 02/16/2011 - 17:48.

very good explanation

Good example.......Thanks

Submitted by Anonymous on Fri, 12/17/2010 - 23:47.

Good example.......Thanks

very Good One.

Submitted by Anonymous on Thu, 12/23/2010 - 19:09.

very Good One.

nice demonstration .. like it

Submitted by Anonymous on Thu, 12/30/2010 - 15:34.

nice demonstration .. like it !

thanks a lot... saved a lot

Submitted by Anonymous on Thu, 01/06/2011 - 15:11.

thanks a lot... saved a lot of time of me..many many thanks :)

Good Example..Thanks a lot

Submitted by Anonymous on Fri, 01/07/2011 - 22:35.

Good Example..Thanks a lot

This is a very good Example

Submitted by Anonymous on Sun, 01/16/2011 - 18:53.

This is a very good Example for Comparator.Kindly provide some more examples by using Hashmaps.

very nice example

Submitted by Anonymous on Tue, 01/18/2011 - 12:47.

very nice example

Good Example

Submitted by Anonymous on Tue, 01/18/2011 - 14:43.

Good Example

thanks cool nice one

Submitted by Anonymous on Fri, 01/21/2011 - 14:01.

thanks cool nice one

To the point and broad

Submitted by Anonymous on Mon, 01/24/2011 - 12:46.

To the point and broad coverage tutorial.......Thanks....... I would like to add that - "The beauty of Comparator is that developer can add many sort sequences."

very good example .u are the

Submitted by Anonymous on Wed, 01/26/2011 - 23:57.

very good example .u are the only person who clears my doubts on this comparator interface

nice and simple to understand

Submitted by Anonymous on Mon, 01/31/2011 - 12:25.

nice and simple to understand example

thanks a lot ...........it

Submitted by Anonymous on Tue, 02/01/2011 - 10:18.

thanks a lot ...........it really helped me

Great Example Thanks a lot

Submitted by Anonymous on Thu, 02/03/2011 - 15:00.

Great Example Thanks a lot

i want to know why we dont

Submitted by Anonymous on Sun, 02/06/2011 - 19:52.

i want to know why we dont implement the equals() method in our comparator class...

Excelent example, simple,

Submitted by Anonymous on Thu, 02/10/2011 - 01:42.

Excelent example, simple, easy thank you

Should implement Comparator

Submitted by Anonymous on Thu, 02/10/2011 - 20:50.

Should implement Comparator and should check for nulls.

Should implement

Submitted by Anonymous on Thu, 02/10/2011 - 20:51.

Should implement Comparator<Employee> and should check for nulls.

+1. This article shows up as

Submitted by Anonymous on Wed, 11/02/2011 - 02:37.

+1. This article shows up as the first Google result for "comparator example". Imagine all the new Java code in the world being copy-pasted from this. I guess I will always have a job.

nice example

Submitted by Anonymous on Sun, 02/13/2011 - 23:56.

nice example

Really nice. Thank you so

Submitted by Anonymous on Sun, 02/20/2011 - 12:06.

Really nice. Thank you so much.

Good and stright example.

Submitted by Anonymous on Tue, 02/22/2011 - 12:17.

Good and stright example. Thanks !

Its vey nice

Submitted by Anonymous on Wed, 02/23/2011 - 16:17.

Its vey nice example...................

Easy to understand :)

Submitted by Anonymous on Wed, 02/23/2011 - 21:26.

Easy to understand :)

very very good example .

Submitted by Anonymous on Fri, 02/25/2011 - 14:20.

very very good example .

nice way to explain

Submitted by Anonymous on Wed, 03/02/2011 - 23:24.

nice way to explain

A clean and clear Example.

Submitted by Anonymous on Sat, 03/12/2011 - 07:10.

A clean and clear Example. good explanation

Hi I have list of Beans with

Submitted by Anonymous on Mon, 03/14/2011 - 12:51.

Hi I have list of Beans with 3 proprties of Employee Bean(name, age, address) I have Taken Address comparator Class shown in below. public class AddressComparitor implements Comparator{ public int compare(Bean bean1,Bean bean2) { int returns=bean1.getAddress().compareTo(bean2.getAddress()); return returns; } } ArrayList list=new ArrayList(); list.add("XXX",25,"12-3-hyd"); list.add("aaa",56,"AD Road-Delhi"); list.add("YYY",23,"45-KKD"); list.add("bbbb",56,"BRRoad-Delhi"); // Sorting.. Colelctions.sort(list,new AddressComparitor()); // Sorting as per Address and display System.out.println("...Sorting as per address........"); for(int i=0;i