Sort ArrayList inside ArrayList

Question

How I can sort skills which is inside another ArrayList as descending order? We have an Employee class with id, name and skills. Skills is a separate list.

public static void main(String[] args) {

    List<Employee> employees = Arrays.asList(
            new Employee(101, "Ehsan", Arrays.asList("Java", "Spring Boot", "Hibernate", "Spring", "Java", "Net")),
            new Employee(102, "Jamshid", Arrays.asList("Java", "Marketing")),
            new Employee(103, "KK",
                    Arrays.asList("Payroll Management", "Human Resource", "Leaves", "Time Sheet")),
            new Employee(104, "Priya", Arrays.asList("Medicine", "Surgery")));


    
  
    
   for(Employee l: employees) {
       System.out.println(l);
   }

    
}

Expected o/p:
Ehsan : {[Java, Spring Boot, Hibernate, Spring, Java, Net]} 
KK : {[Payroll Management, Human Resource, Leaves, Time Sheet]} 
Jamshid : {[Java, Marketing]} 
Priya : {[Medicine, Surgery]}

If you need it all the time, the constructor of Employee could sort the list it gets. — tevemadar
– tevemadar, Commented Aug 13, 2020 at 22:19
Note that Arrays.asList does not return a java.util.ArrayList. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Aug 13, 2020 at 22:19
List itself has sort() in any contemporary Java version: docs.oracle.com/javase/8/docs/api/java/util/… - oh, maybe that remark was about the tag. — tevemadar
– tevemadar, Commented Aug 13, 2020 at 22:22

Unmitigated · Accepted Answer · 2020-08-13 22:52:30Z

1

You can use Comparator.comparingInt to sort based on the sizes of the skills List.

employees.sort(Comparator.<Employee>comparingInt(e -> e.getSkills().size()).reversed());

Before Java 8, you can use the following:

employees.sort(new Comparator<Employee>() {
    @Override
    public int compare(final Employee o1, final Employee o2) {
       return Integer.compare(o2.getSkills().size(), o1.getSkills().size());
    }
});

edited Aug 13, 2020 at 22:52

answered Aug 13, 2020 at 22:18

Unmitigated

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8 Comments

tevemadar Over a year ago

For added fun, OP wanted descending order :-)

ehsan hosseini Over a year ago

I mean with descending order this way: Ehsan has 6 skills so it comes first and KK has 4 skills and comes in second and so on.

ehsan hosseini Over a year ago

Can you use Java 7 for your answer?

Unmitigated Over a year ago

@ehsanhosseini Updated.

Unmitigated Over a year ago

@ehsanhosseini Glad to help.

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