-> Comparator used to sorting the object element by using multiple sorting sequence.
-> We can sort the elements on the basis of any data member, for example, rollno, name, age or anything else.
-> The comparator interface provide two methods like compare(Object obj1,Object obj2) and equals(Object obj).
1) compare(Object obj1,Object obj2) function
Its compares first object(obj1) and second object(obj2) and return int value
Syntax : public int compare(Object obj1,Object obj2)
positive integer = if the current object is greater than the specified object.
negative integer = if the current object is less than the specified object.
zero = if the current object is equal to the specified object.
2) equals(Object obj1) function
Its used to compare current object with specified object
Syntax : public boolean equals(Object obj1)
Example : Sorting by name and Emp id by using comparator
import java.util.*;
import java.io.*;
// User - Defined Class
class Employee {
int empid;
String empname;
int empage;
Employee(int empid,String empname,int empage){
this.empid=empid;
this.empname=empname;
this.empage=empage;
}
}
class sortByAge implements Comparator{
public int compare(Object o1,Object o2){
Employee s1=(Employee)o1;
Employee s2=(Employee)o2;
if(s1.empage==s2.empage)
return 0;
else if(s1.empage>s2.empage)
return 1;
else
return -1;
}
}
class sortByName implements Comperator{
public int compare(Object o1,Object o2){
Employee s1=(Employee)o1;
Employee s2=(Employee)o2;
return s1.empname.compareTo(s2.empname);
}
}
// Main Class
public class TestSort1{
public static void main(String args[]){
ArrayList<Employee> al=new ArrayList<Employee>();
al.add(new Employee(1,"Ajith",23));
al.add(new Employee(6,"Vijay",27));
al.add(new Employee(4,"Surya",21));
System.out.println("Sorting By Age");
Collections.sort(al, new sortByAge());
for(Employee st:al){
System.out.println(st.empid+" "+st.empname+" "+st.empage);
}
System.out.println("Sorting By Name");
Collections.sort(al, new sortByName());
for(Employee st:al){
System.out.println(st.empid+" "+st.empname+" "+st.empage);
}
}
}
Output
Sorting By Age
4 Surya 21
1 Ajith 23
6 Vijay 27
Sorting By Name
1 Ajith 23
4 Surya 21
6 Vijay 27
