sorting - How to sort Arraylist consisting of pojo class in java -

i have pojo class student this

class student {     private int score;     private string firstname;     //getters , setters ................. } 

i creating arraylist this

public static void main(string[] args) {     list<student> al_students= new arraylist<student>();     student s1= new student();     s1.setscore(90);     s1.setfirstname("abc");     al_students.add(s1);      student s2= new student();     s2.setscore(95);     s2.setfirstname("def");     al_students.add(s2);      student s3= new student();     s3.setscore(85);     s3.setfirstname("xyz");     al_students.add(s3); } 

now want sort based on scores in descending order i.e
output

1)def      95 2)abc      90 3)xyz      85 

you can use custom comparator.

here's full example (imports excluded):

public class main {      // main method setting , printing students     public static void main(string[] args) {         list<student> students = new arraylist<student>();         student s1 = new student();         s1.setscore(90);         s1.setfirstname("abc");         students.add(s1);          student s2 = new student();         s2.setscore(95);         s2.setfirstname("def");         students.add(s2);          student s3 = new student();         s3.setscore(85);         s3.setfirstname("xyz");         students.add(s1);         system.out.printf("unordered: %s%n", students);         // sorting using anonymous comparator         collections.sort(students, new comparator<student>() {             public int compare(student s1, student s2) {                 // notice cast (integer) invoke compareto                 return ((integer)s1.getscore()).compareto(s2.getscore());             }         });         system.out.printf("ordered: %s%n", students);     }     // student class     static class student {         private int score;         private string firstname;         // boring stuff         public int getscore() {             return score;         }          public void setscore(int score) {             this.score = score;         }          public string getfirstname() {             return firstname;         }          public void setfirstname(string name) {             this.firstname = name;         }         // printing         @override         public string tostring() {             return string.format("student \"%s\" score: %d%n", firstname,                     score);         }     } } 

output

unordered: [student "abc" score: 90 , student "def" score: 95 , student "abc" score: 90 ] ordered: [student "abc" score: 90 , student "abc" score: 90 , student "def" score: 95 ] 

note

as others mention, can implement comparable<student> in student class, if (or default) sorting score.#

second edit

in order sort in decreasing order, can replace return statement in comparator following:

return ((integer)s2.getscore()).compareto(s1.getscore()); 

thanks programminglover spotting / apologies mistakenly rejecting edit!