sort a list of different type of objects

Question

I have a list of objects which contains different types of objects but a single property is common among all. list contains objects of Field class, Button Class, Page class

Answer 1

If there are a few classes you want to sort (Field,Button,Page...) you could do a Class that inherits from Comparator<Object> and use the java.lang.Object.getClass() and casting in an switch clasusule.

Something like:

public class MyComparator implements Comparator<Object>{
        @Override
        public int compare(Object o1, Object o2) {
            int o1prop,o2prop;
            switch (o1.getClass().toString()) {
            case "java.Button":
                ((Button)o1prop).getSequence_no();
                break;

            default:
                break;
            }

            switch (o2.getClass().toString()) {
            case "java.Field":
                ((Field)o1prop).getSequence_no();
                break;

            default:
                break;
            }

            return o1prop-o2prop;
        }

And after that use:

Collections.sort(list, new MyComparator());

Answer 2

I'd suggest creating an interface, something like "Sequenceable" with a method getSequenceNo().

public interface Sequenceable {
    int getSequenceNo();
}

Your Field, Button, Page classes should implement this interface and the getSequenceNo() method will return your sequence_no.

Then you can implement your own Comparator and sort using this comparator.

For example, your comparator will look like:

class MyComparator implements Comparator<Sequenceable> {

    @Override
    public int compare(Sequenceable o1, Sequenceable o2) {
        return o2.getSequenceNo() - o1.getSequenceNo();
    }
}

Then you can sort with:

Collections.sort(list, new MyComparator());

Answer 3

The best and clean way is to have your class implementing an interface or extending a common base class .

Other way can be (which i don't prefer becpz of performance, readability and cleanliness), create a custom comparator that uses reflection which checks the type and then compare the property

Answer 4

All your objects should be exetended or inheritance by some and same super class, then the compiler will not ask you to explicitly change those objects.