Question

I have a list of java beans, now I want to sort them with specified property and sort order
(the property and sort order are input parameters), like this:

class Person{
    private String userName;
    private Integer age;
    private String address; 

    public void sort(List<Person> ps, String property, String sortOrder)
    {
        // How to use the property and sortOrder??
        Collections.sort(ps);
    }
}

What is the best way of writing the sortList() method?
actually I have one way to do this. I can write two static properties for Person. then I set these two properties before sorting:

class Person implements Comparable<Person>{
    private String userName;
    private Integer age;
    private String address;
    public static String sortProperty;
    public static String sortOrder;

    public void sort(List<Person> ps, String property, String sortOrder)
    {
        Person.sortProperty=property;
        Person.sortOrder=sortOrder;

        Collections.sort(ps);
    }

    @Override
    public int compareTo(Person o)
    {
        // find the property with Person.sortProperty using reflection
        // then sort the property
    }
}

This is not a good solution. Could anyone give me some suggestion? thanks in advance

Answer 1

Hope this makes sense for you. Use final keyword to avoid creating static variable for passing sort order. Also changed it to boolean for easy access. Below code is just for illustration.

public static void sort(List<Person> ps, String property, final boolean asc) {

  if (property.equals("userName")) {
    Collections.sort(ps, new Comparator<Person>() {

        public int compare(Person o1, Person o2) {
            // pls use appropriate compareTo I always get confused
            // which one to call when it is asc or desc.
            if (asc)
                return o1.getUserName().compareTo(o2.getUserName());
            else
                return o2.getUserName().compareTo(o1.getUserName());
        }
    });
  }

  if (property.equals("age")) {
    Collections.sort(ps, new Comparator<Person>() {

        public int compare(Person o1, Person o2) {

            if (asc)
                return o1.getAge().compareTo(o2.getAge());
            else
                return o2.getAge().compareTo(o1.getAge());
        }
    });
  }
}