custom omparator for list in 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: collections.sort custom comparator

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());