How to Sort a List by Different Parameters at Different Timed

How do I sort a list by different parameters at different timed

I think your enum approach is basically sound, but the switch statements really need a more object oriented approach. Consider:

enum PersonComparator implements Comparator<Person> {
    ID_SORT {
        public int compare(Person o1, Person o2) {
            return Integer.valueOf(o1.getId()).compareTo(o2.getId());
        }},
    NAME_SORT {
        public int compare(Person o1, Person o2) {
            return o1.getFullName().compareTo(o2.getFullName());
        }};

    public static Comparator<Person> decending(final Comparator<Person> other) {
        return new Comparator<Person>() {
            public int compare(Person o1, Person o2) {
                return -1 * other.compare(o1, o2);
            }
        };
    }

    public static Comparator<Person> getComparator(final PersonComparator... multipleOptions) {
        return new Comparator<Person>() {
            public int compare(Person o1, Person o2) {
                for (PersonComparator option : multipleOptions) {
                    int result = option.compare(o1, o2);
                    if (result != 0) {
                        return result;
                    }
                }
                return 0;
            }
        };
    }
}

An example of usage (with a static import).

public static void main(String[] args) {
    List<Person> list = null;
    Collections.sort(list, decending(getComparator(NAME_SORT, ID_SORT)));
}

Sort a list by multiple attributes?

A key can be a function that returns a tuple:

s = sorted(s, key = lambda x: (x[1], x[2]))

Or you can achieve the same using itemgetter (which is faster and avoids a Python function call):

import operator
s = sorted(s, key = operator.itemgetter(1, 2))

And notice that here you can use sort instead of using sorted and then reassigning:

s.sort(key = operator.itemgetter(1, 2))

Sort list of strings by multiple parameters

Two mistakes in your code.

1. You'll need to provide the generic parameters to comparing
2. naturalOrder returns a comparator; invoke it, rather than passing a reference

Try:

        words.sort(Comparator.<String, Integer>comparing(o -> countChar(c,  o))
                         .thenComparing(Comparator.naturalOrder()));

How can I sort a list of Java objects based on parameters that a user selects from a drop down menu?

You can try creating an enum:

public enum FileInfoComparator {
    FILE_NAME(Comparator.comparing(FileInfo::getFileName)),
    TIMESTAMP(Comparator.comparing(FileInfo::getTimestamp)),
    SIZE(Comparator.comparing(FileInfo::getSize)),
    // ... add other criteria here
    ;

    private final Comparator<FileInfo> comparator;

    FileInfoComparator(Comparator<FileInfo> comparator) {
        this.comparator = comparator;
    }

    static Comparator<FileInfo> by(String key, boolean ascending) {
        Comparator<FileInfo> comparator = valueOf(key).comparator;
        return ascending ? comparator : comparator.reversed();
    }

    static Comparator<FileInfo> by(Pair<String, Boolean> criterion) {
        return by(criterion.getKey(), criterion.getValue());
    }

    static Optional<Comparator<FileInfo>> by(List<Pair<String, Boolean>> criteria) {
        return criteria.stream()
                .map(FileInfoComparator::by)
                .filter(Objects::nonNull)
                .reduce(Comparator::thenComparing);
    }

}

Then use:

// Create the list of selected criteria based on user input:
// E.g. [FILE_NAME, false] will mean "sort by fileName descending"
List<Pair<String, Boolean>> selectedCriteria = ...

// Build your comparator and sort your list
FileInfoComparator.by(selectedCriteria).ifPresent(files::sort);

In case of empty user selection the files will remain untouched.

How to perform a series of sort operation on arraylist (multiple sort criteria)

  Collections.sort(myList, new Comparator() {

     @Override
     public int compare(Object o1, Object o2)
     {
        // write your ordering code here
        return 0;
     }

  });

Just fill in the code for the comparison you want and Java will handle the sorting for you.

Edit for updated question:

Comparator<Ticket> mc;
mc = new TicketIdComparator();
Collections.sort(tickets, mc);

final class TicketIdComparator implements Comparator<Ticket>

{

    @Override
    public int compare(Ticket ticket1, Ticket ticket2) {
        String TicketId1 = ((Ticket) ticket1).getNumber();
        String TickedId2 = ((Ticket) ticket2).getNumber();

        int num1=Integer.parseInt(TicketId1);
        int num2 =Integer.parseInt(TickedId2);

        if (num1<num2)
            return 1;
        else if (num1>num2)
            return -1;
        else
            return ticket1.getName().compare(ticket2.getName());
    }
}

Collections.sort with multiple fields

Do you see anything wrong with the code?

Yes. Why are you adding the three fields together before you compare them?

I would probably do something like this: (assuming the fields are in the order you wish to sort them in)

@Override public int compare(final Report record1, final Report record2) {
    int c;
    c = record1.getReportKey().compareTo(record2.getReportKey());
    if (c == 0)
       c = record1.getStudentNumber().compareTo(record2.getStudentNumber());
    if (c == 0)
       c = record1.getSchool().compareTo(record2.getSchool());
    return c;
}

Sort a list of different objects with the same property (timestamp) in Flutter/Dart

I think the problem is that you have a list with dynamic type. Therefore I would recommend creating an abstract class that contains both information from ClassA and ClassB, so that the dart compiler understands.

List<Parent> _list = [
  ClassA(DateTime(2020, 04, 04)),
  ClassB(DateTime(2020, 03, 04)),
  ClassA(DateTime(2020, 02, 04)),
  ClassB(DateTime(2020, 01, 04))
];

_list.sort((a,b)=> b.createdAt.compareTo(a.createdAt));

abstract class Parent {
  DateTime createdAt;
}

class ClassA implements Parent {
  DateTime createdAt;
  ClassA(this.createdAt);
}

class ClassB implements Parent {
  DateTime createdAt;
  ClassB(this.createdAt);
}

Here is also a CodePen where I could sort the list.

https://codepen.io/md-weber/pen/RwWaMgz

How can I sort an ArrayList of objects?

Well you just need to change your comparison function to include other fields like this

    Collections.sort(contacts, (Contact c1, Contact c2) -> {
        int firstNameComparisonResult = c1.getFirstName().compareTo(c2.getFirstName());
        if (firstNameComparisonResult != 0) {
            return firstNameComparisonResult;
        } else {
            return c1.getLastName().compareTo(c2.getLastName());
        }
    });

Warning: this assumes there are no nulls.

Full code I used if you want to take a look:

class Contact{
    final String firstName;
    final String lastName;
    final int age;

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public int getAge() {
        return age;
    }

    public Contact(String firstName, String lastName, int age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Contact{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", age=" + age +
                '}';
    }
}

@Test
public void sortTest(){
    List<Contact> contacts = new ArrayList<>();
    contacts.add(new Contact("A","B",37));
    contacts.add(new Contact("A","C",34));
    contacts.add(new Contact("B","A",35));

    Collections.sort(contacts, (Contact c1, Contact c2) -> {
        int firstNameComparisonResult = c1.getFirstName().compareTo(c2.getFirstName());
        if (firstNameComparisonResult != 0) {
            return firstNameComparisonResult;
        } else {
            return c1.getLastName().compareTo(c2.getLastName());
        }
    });

    System.out.println(contacts);
 //[Contact{firstName='A', lastName='B', age=37}, Contact{firstName='A', lastName='C', age=34}, Contact{firstName='B', lastName='A', age=35}]

}

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