Java Sorting using Comparator

Pavan May 24, 2010 Java 4 Comments

Lets see how we can sort our Employee objects using different criteria like id, name, salary.

SortTest remains the main class that will perform creating and filling objects for us. This time employee class is plain old java classs that holds some data about each employee we create.

Here I have created scenarios or you can say strategies OR classes for sorting as SortById, SortByName, SortBySalary. Each of above class implements comparator interface and overrides compare method, which takes two objects to compare and return eithre -1, 1 or 0.

Note: I have added few helper functions that really helps while coding like print – this takes array list of objects and prints in format I want instead of class id and all that. toString – overridden this function so I can return the class string as required

Here goes the code –

import java.util.*;

public class SortTest
{
	public static void main(String args[])
	{
		new SortTest();
	}

	public SortTest()
	{
		//fill some employee objects
		ArrayList list = new ArrayList();
		list.add(new Employee(500,"Shifoo",150000));
		list.add(new Employee(504,"Oogway",120000));
		list.add(new Employee(503,"Tigress",100000));
		list.add(new Employee(730,"Mantis",45000));

		System.out.println("Initial List :");
		print(list);
		System.out.println("n");

		Collections.sort(list,new SortyById());
		System.out.println("Sorted List By Id:");
		print(list);
		System.out.println("n");

		Collections.sort(list,new SortyByName());
		System.out.println("Sorted List By Name:");
		print(list);
		System.out.println("n");

		Collections.sort(list,new SortyBySalary());
		System.out.println("Sorted List By Salary:");
		print(list);
		System.out.println("n");

	}

	public void print(ArrayList list)
	{
		Iterator it = list.iterator();
		while(it.hasNext())
		{
			Employee emp = (Employee) it.next();
			System.out.println(emp);
		}
	}
}

class Employee
{
	public int id;
	public String name;
	public double salary;

	public Employee(int id, String name,double salary )
	{
		this.id = id;
		this.name = name;
		this.salary = salary;
	}

	public String toString()
	{
		return this.id +", "+this.name+", "+this.salary;
	}
}

//scenario | strategy - I
class SortyById implements Comparator
{
	public int compare(Object object1, Object object2)
	{
		int value=0;

		Employee emp1 = (Employee) object1;
		Employee emp2 = (Employee) object2;

		if(emp1.id > emp2.id)
			value = 1;
		else if(emp1.id < emp2.id)
			value = -1;
		else if(emp1.id == emp2.id)
			value = 0;

		return value;
	}
}

//scenario | strategy - II
class SortyByName implements Comparator
{
	public int compare(Object object1, Object object2)
	{
		Employee emp1 = (Employee) object1;
		Employee emp2 = (Employee) object2;

		return emp1.name.compareTo(emp2.name);
	}
}

//scenario | strategy - III
class SortyBySalary implements Comparator
{
	public int compare(Object object1, Object object2)
	{
		int value=0;

		Employee emp1 = (Employee) object1;
		Employee emp2 = (Employee) object2;

		if(emp1.salary > emp2.salary)
			value = 1;
		else if(emp1.salary < emp2.salary)
			value = -1;
		else if(emp1.salary == emp2.salary)
			value = 0;

		return value;
	}
}

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

import java.util.*;

public class SortTest

{

public static void main(String args[])

{

new SortTest();

}

public SortTest()

{

//fill some employee objects

ArrayList list = new ArrayList();

list.add(new Employee(500,"Shifoo",150000));

list.add(new Employee(504,"Oogway",120000));

list.add(new Employee(503,"Tigress",100000));

list.add(new Employee(730,"Mantis",45000));

System.out.println("Initial List :");

print(list);

System.out.println("n");

Collections.sort(list,new SortyById());

System.out.println("Sorted List By Id:");

print(list);

System.out.println("n");

Collections.sort(list,new SortyByName());

System.out.println("Sorted List By Name:");

print(list);

System.out.println("n");

Collections.sort(list,new SortyBySalary());

System.out.println("Sorted List By Salary:");

print(list);

System.out.println("n");

}

public void print(ArrayList list)

{

Iterator it = list.iterator();

while(it.hasNext())

{

Employee emp = (Employee) it.next();

System.out.println(emp);

}

class Employee

{

public int id;

public String name;

public double salary;

public Employee(int id, String name,double salary )

{

this.id = id;

this.name = name;

this.salary = salary;

}

public String toString()

{

return this.id +", "+this.name+", "+this.salary;

}

//scenario | strategy - I

class SortyById implements Comparator

{

public int compare(Object object1, Object object2)

{

int value=0;

Employee emp1 = (Employee) object1;

Employee emp2 = (Employee) object2;

if(emp1.id > emp2.id)

value = 1;

else if(emp1.id < emp2.id)

value = -1;

else if(emp1.id == emp2.id)

value = 0;

return value;

}

//scenario | strategy - II

class SortyByName implements Comparator

{

public int compare(Object object1, Object object2)

{

Employee emp1 = (Employee) object1;

Employee emp2 = (Employee) object2;

return emp1.name.compareTo(emp2.name);

}

//scenario | strategy - III

class SortyBySalary implements Comparator

{

public int compare(Object object1, Object object2)

{

int value=0;

Employee emp1 = (Employee) object1;

Employee emp2 = (Employee) object2;

if(emp1.salary > emp2.salary)

value = 1;

else if(emp1.salary < emp2.salary)

value = -1;

else if(emp1.salary == emp2.salary)

value = 0;

return value;

}

Output:

Initial List :
500, Shifoo, 150000.0
504, Oogway, 120000.0
503, Tigress, 100000.0
730, Mantis, 45000.0


Sorted List By Id:
500, Shifoo, 150000.0
503, Tigress, 100000.0
504, Oogway, 120000.0
730, Mantis, 45000.0


Sorted List By Name:
730, Mantis, 45000.0
504, Oogway, 120000.0
500, Shifoo, 150000.0
503, Tigress, 100000.0


Sorted List By Salary:
730, Mantis, 45000.0
503, Tigress, 100000.0
504, Oogway, 120000.0
500, Shifoo, 150000.0

As you can see –

we can create multiple sort strategy for sorting
we can compare heterogeneous objects

Tags:comparator, Java, sorting

4 Comments

Guru
December 31, 2012 | Reply

Nice example to separate two object comparing example
Nagarjun
July 9, 2012 | Reply

This really helping..!! Thank you
Gift vincy
June 25, 2010 | Reply

Nice post. The example code was very useful for clear understating.

Pavan
June 25, 2010 | Reply

Cool, I am happy it helped you.

Sunbelt Computer Software

PL/B Language Development and Support

Java Sorting using Comparator

Add a Comment

Openstrap 2.0.3

Aadya 2.0.3

Awakening 2.0.3

Sunbelt Computer Software

PL/B Language Development and Support

Related Posts

Add a Comment

Openstrap 2.0.3

Aadya 2.0.3

Awakening 2.0.3