Java-对ArrayList中的对象进行排序 <Car> 基于MPG

Question

I am having issues (using a modified version of SelectionSort) to sort the ArrayList of Car objects from lowest MPG to greatest MPG . Here is my code:

public ArrayList<Car> getSortedByMPG(){

     ArrayList<Car> bestMPG = new ArrayList<Car>();
     bestMPG.addAll(myCars);

     int smallestIndex;
     Car smallest;
     Car smallest1;
     double smallestMPG;
     double smallestMPG1;

     for (int curIndex = 0; curIndex < bestMPG.size(); curIndex++) {
         smallest = bestMPG.get(curIndex);
         smallestMPG = smallest.getMPG();
         smallestIndex = curIndex;

         for (int i = curIndex + 1; i < bestMPG.size(); i++) {
             smallest1 = bestMPG.get(i);
             smallestMPG1 = smallest1.getMPG();
             if (smallestMPG > smallestMPG1) {
                smallest = bestMPG.get(i);
                smallestIndex = i;
             }
         }

         if (smallestIndex != curIndex) {
               Car temp = bestMPG.get(curIndex);
               bestMPG.set(curIndex, bestMPG.get(smallestIndex));
               bestMPG.set(smallestIndex, temp);
         }

     }

     return bestMPG;

}

There is a tester class for this method, however, I do not want to post it (to avoid getting trolled for code dumping). I have worked on this for a few hours now and cannot figure out why this code is not sorting. If anyone can offer any advice it would be much appreciated.

EDIT: Thank you all for the responses. I realize I did not do the proper research beforehand, but that is why I come to StackOverflow! You guys teach me things daily.

Here is how I solved it, thanks to Aomine:

public ArrayList<Car> getSortedByMPG(){

       ArrayList<Car> bestMPG = new ArrayList<Car>();
       bestMPG.addAll(myCars);

       Collections.sort(bestMPG, Comparator.comparingDouble(Car::getMPG));

       return bestMPG;
}

Answer 1

one of several ways to sort your list is by using the List.sort method and passing in a comparator object. Ie:

bestMPG.sort(Comparator.comparingDouble(Car::getMpg));

then you can just return bestMPG .

Answer 2

If I understood your question, you can use Collections.sort

        ArrayList<Car> bestMPG = new ArrayList<Car>();

        Collections.sort(bestMPG, new Comparator<Car>() {

            public int compare(Car c1, Car c2) {
                Double mpg1 = c1.getMpg();
                Double mpg2 = c2.getMpg();

                return mpg1.compareTo(mpg2);
            }
        });