sort list of objects java code example

Example 1: sort list of objects by attribute java

ArrayList<Employee> employees = getUnsortedEmployeeList();
             
Comparator<Employee> compareById = (Employee o1, Employee o2) -> o1.getId().compareTo( o2.getId() );
 
Collections.sort(employees, compareById);
 
Collections.sort(employees, compareById.reversed());

Example 2: how to sort the arraylist of objects in java

package beginnersbook.com;
import java.util.*;
public class Details  {

	public static void main(String args[]){
	   ArrayList<Student> arraylist = new ArrayList<Student>();
	   arraylist.add(new Student(101, "Zues", 26));
	   arraylist.add(new Student(505, "Abey", 24));
	   arraylist.add(new Student(809, "Vignesh", 32));

	   /*Sorting based on Student Name*/
	   System.out.println("Student Name Sorting:");
	   Collections.sort(arraylist, Student.StuNameComparator);

	   for(Student str: arraylist){
			System.out.println(str);
	   }

	   /* Sorting on Rollno property*/
	   System.out.println("RollNum Sorting:");
	   Collections.sort(arraylist, Student.StuRollno);
	   for(Student str: arraylist){
			System.out.println(str);
	   }
	}
}

Example 3: how to sort collection in java

// Use Collections.sort()
import java.util.*;
ArrayList<String> al = new ArrayList<String>();
al.add("teach");
al.add("sleep");
al.add("geek");
Collections.sort(al);//just pass any collection object reference
System.out.println(al);//output :- [geek,sleep,teach]

or
/*
ArrayList<Integer> intal = new ArrayList<Integer>();
al.add(4);
al.add(8);
al.add(2);
Collections.sort(intal);
System.out.println(intal);//output :- [2,4,8]
*/

Example 4: how to sort the arraylist of objects in java

package beginnersbook.com;
import java.util.Comparator;
public class Student  {
    private String studentname;
    private int rollno;
    private int studentage;

    public Student(int rollno, String studentname, int studentage) {
        this.rollno = rollno;
        this.studentname = studentname;
        this.studentage = studentage;
    }
    ...
    //Getter and setter methods same as the above examples
    ...
    /*Comparator for sorting the list by Student Name*/
    public static Comparator<Student> StuNameComparator = new Comparator<Student>() {

	public int compare(Student s1, Student s2) {
	   String StudentName1 = s1.getStudentname().toUpperCase();
	   String StudentName2 = s2.getStudentname().toUpperCase();

	   //ascending order
	   return StudentName1.compareTo(StudentName2);

	   //descending order
	   //return StudentName2.compareTo(StudentName1);
    }};

    /*Comparator for sorting the list by roll no*/
    public static Comparator<Student> StuRollno = new Comparator<Student>() {

	public int compare(Student s1, Student s2) {

	   int rollno1 = s1.getRollno();
	   int rollno2 = s2.getRollno();

	   /*For ascending order*/
	   return rollno1-rollno2;

	   /*For descending order*/
	   //rollno2-rollno1;
   }};
    @Override
    public String toString() {
        return "[ rollno=" + rollno + ", name=" + studentname + ", age=" + studentage + "]";
    }

}