Comparators

Comparator Class

One level of Comparisons

class Student {    int rollno;    String name, address;}class SortByName implements Comparator<Student> {    // Sorting in ascending order of Name.    public int compare(Student a, Student b) {        return a.name.compareTo(b.name);    }}class SortByRoll implements Comparator<Student> {    // Sorting in ascending order of Roll No.    public int compare(Student a, Student b){        return a.rollno - b.rollno;    }}class Solution {    public static void main(String[] args) {                Collections.sort(studentsArray, new SortByRoll());        }}

Two levels of Comparisons.

class Student {    String Name;    int Age;}class CustomerSortingComparator implements Comparator<Student> {    @Override    public int compare(Student customer1, Student customer2) {    int NameCompare = customer1.Name.compareTo(customer2.Name);    int AgeCompare = customer1.Age.compareTo(customer2.Age);    // 2nd level comparison    return (NameCompare == 0) ? AgeCompare : NameCompare;    }}class Solution {    Collections.sort(al,new CustomerSortingComparator());}