N:B: If you have not gone through my previous post about comparator then once go through the link Comparable & Comparator: then it will be easy to understand this topic.
Comparator:
- Java Comparator interfaceis used to order the objects of user-defined class.
- It is basically used for custom sorting, that means you can sort employee objects by name by salary.
- Comparator interface is in java.util package and its having one method compare() which takes two user defined objects as argument.
public int compare(Object obj1,Object obj2)
- Compare() method compares first object data member with second object data member and its return type is “int”.
- While shorting through Collections.sort() method we have to pass the Collection object as well as the Comparator object.
- Let me discuss it though examples.
Employee.java:
| package com.tcoj.model;
public class Employee { int id; public String name; public double salary; @Override public String toString() {
return “[“+id+”,”+name+”,”+salary+”]”; } public Employee(int id, String name, double salary) { super(); this.id = id; this.name = name; this.salary = salary; } } |
- Now Let me write two comparators one as NameComparator another SalaryComparator for two custom comparing.
- The Idea here is to compare the Employee objects through different fields.
NameComparator.java:
| import java.util.Comparator;
import com.tcoj.model.Employee;
public class NameComparator implements Comparator<Employee> {
@Override public int compare(Employee emp1, Employee emp2) {
return emp1.name.compareTo(emp2.name); }
} |
SalaryComarator.java:
| import java.util.Comparator;
import com.tcoj.model.Employee;
public class SalaryComparator implements Comparator<Employee> {
@Override public int compare(Employee emp1, Employee emp2) { double d=emp1.salary-emp2.salary; if(d>0) return 1; else if(d < 0) return -1; else return 0; } } |
- Now Let me write the client class where I will add some Employee objects and add them to list.
- Then after passing two different Comparator objects we will see the sorting.
Client.java:
| package com.tcoj.clint;
import java.util.ArrayList; import java.util.Collections; import java.util.Iterator; import java.util.List;
import com.tcoj.comparators.NameComparator; import com.tcoj.comparators.SalaryComparator; import com.tcoj.model.Employee;
public class Clint {
public static void main(String[] args) { List<Employee> list=new ArrayList<Employee>(); Employee emp1=new Employee(102, “shaswot”, 11500.89); Employee emp2=new Employee(100, “subham”, 12500.89); Employee emp3=new Employee(107, “ashok”, 11500.99); Employee emp4=new Employee(108, “rahul”, 13501.09);
list.add(emp1); list.add(emp2); list.add(emp3); list.add(emp4); Collections.sort(list,new NameComparator()); //passing namecomparator object Iterator<Employee> itr=list.iterator(); System.out.println(“Sort by name=============================”); while(itr.hasNext()) { System.out.println(itr.next()); } System.out.println(“Sort by Salary===========================”); Collections.sort(list,new SalaryComparator()); //passing salarycomparator object Iterator<Employee> itr1=list.iterator(); while(itr1.hasNext()) { System.out.println(itr1.next()); } } } |
Output:
| Sort by name=============================
[107,ashok,11500.99] [108,rahul,13501.09] [102,shaswot,11500.89] [100,subham,12500.89] Sort by Salary=========================== [102,shaswot,11500.89] [107,ashok,11500.99] [100,subham,12500.89] [108,rahul,13501.09]
|
- Here you can see when I am passing NameComparator it is sorting by name and same in SalaryComparator also.
If You guys have any doubt on this topic then feel free to comment and ask questions.
The Cup Of Java 