比较arraylist中不同的对象值

Question

Depending on user preferences I want to compare object values of an array list and get the max values. My first approach was to define a function for object property and iterate through the array list.

    private MyModel getMaxValueA(ArrayList<MyModel> myModelList) {
    MyModel res = null;
    for (MyModel myModel : myModelList) {
        if (myModel != null) {
            if (myModel.valueA() > res.valueA()) {
                res = myModel;
            }
        } else {
            res = myModel;
        }
    }
    return res;
}

The problem is, i have 4 different values i want to compare, and to define 4 similar funktion does not seem to be the right was, so i tried it to combine all functions and added a switch/case

    private MyModel getMaxValueA(ArrayList<MyModel> myModelList, Setting mySetting) {
    MyModel res = null;
    for (MyModel myModel : myModelList) {
        if (myModel != null) {
            switch (mySetting) {
            case settingA:
                if (myModel.valueA() > res.valueA()) {
                     res = myModel;
                    }
                break;
            case settingB:
                if (myModel.valueB() > res.valueB()) {
                     res = myModel;
                    }

                break;
            ........
        } else {
            res = myModel;
        }
    }
    return res;
}

This is a bit shorter and only 1 instead of 4 functions, but it doesnt make me happy, too. Do you have any ideas to improve it?

Thanks.

Answer 1

Implement all your different needs like this:

class SettingsAComparator extends Comparator<MyModel> {
    @Override
    public int compare(MyModel m1, MyModel m2) {
         return m1.valueA() - m2.valueA();
    }
}

class SettingsBComparator extends Comparator<MyModel> {
    // Please use better names.
    // you can implement as many Comparators as necessary.
}

and change your method to

private MyModel getMaxValue(ArrayList<MyModel> myModelList, Comparator<MyModel> comparator) {
    return Collections.max(myModelList, comparator);
}

This way, you can always add different comparators, if your class gets a new attribute, but you'll never have to worry about changing getMaxValue() again. Also you can implement complex comparators, that take more than one attribute value into account.

Answer 2

Implement a Comparator

 class MyComparator extends Comparator<MyModel> {
     Setting s;
     MyComparator(Setting s ){
        this.setting=s;
     } 
     public int compare(MyModel model, MyModel model2) {
        //do the comparison utilizing setting

     }

Edited looking at another answer: Then use Collections.max(listToBeSorted, new MyComparator(setting)) to get max value