使用比较器在列表中上移元素

Question

I have an ArrayList in Java :

{"PatMic", "PatientDoc", "Phram", "Patnet", "PatientA"}

All the elements have a number assigned : PatMic = 20, PatientDoc = 30, Phram = 40, Patnet = 50, PatientA = 60.

And my current Comparator :

Comparator<String> comparator = new Comparator<String>() {

    @Override
    public int compare(final String o1, final String o2) {            
        final int numbr1 = getElementNumber(); //Returns element's number in a list
        final int numbr2 = getElementNumber();
        if (numbr1 > numbr2 ) {
            return 1;
        } else if (numbr1 < numbr2 ) {
            return -1;
          }            
            return 0;
    }
};
Collections.sort(strings, comparator);

I do not want to change the assigned numbers to each element but would want to move the element PatientA in between PatMic and PatientDoc so the modified list should look like :

{"PatMic", "PatientA" "PatientDoc", "Phram", "Patnet"}

Could someone please suggest how to achieve this? I tried many ways to modify the existing Comparator logic but in vain. Thank you.

Answer 1

You are trying to sort based on some inherent value associated with a String. Therefore, sorting on a String itself is probably not correct. What you probably want to use is either a custom object (implement equals , hashCode and the interface Comparable ), or an enum type. This will allow you to change the internal state of these objects explicitly, which will manifest itself naturally when using a Comparator . For example, using a class:

class MyClass implements Comparable
{
    private String name;
    private int value;

    //Constructor
    public MyClass(String s, int v)
    {
        name = s;
        value = v;
    }

    //Getters and setters

    //Implement comparing method
}

Then you can use these objects in place of your Strings:

//...
MyClass patMic = new MyClass("PatMic", 20);
// So on..

Answer 2

First, you should give you comparator sufficient knowledge about what it should do. I mean you should have some data available to comparator that says something like "okay, sort them all by associated number except this one - place it right here ". " Right here " could be anything that points exact position, I gonna choose " before that element ".

So here we go

public void sortWithException(List<String> data, final Map<String, Integer> numbers, final String element, final String next) {
    Collections.sort(data, new Comparator<String>() {
        @Override
        public int compare(String first, String second) {
            if (first.equals(element) || second.equals(element)) { //the exception
                Integer nextNumber = numbers.get(next);
                Integer firstNumber = numbers.get(first);
                Integer secondNumber = numbers.get(second);
                if (first.equals(element)) {
                    if (next == null) // placing the exception after ANY element 
                        return 1;
                    return secondNumber >= nextNumber ? -1 : 1; //placing the element before next and after all next's predecessors
                } else { // second.equals(element)
                    if (next == null)
                        return -1;
                    return firstNumber >= nextNumber ? 1 : -1;
                }
            } else { //normal sort
                return numbers.get(first) - numbers.get(second);
            }
        }
    });
}

and call it like sortWithException(data, numbers, "PatientA", "PatientDoc")

Note that i used Map for associated numbers, you should probably use your own method to get those numbers.