Sort list based on specific order in java

Question

I have a list of object and need to sort it based on specific order. Something like below code:

preOrderedList = {"bmw","audi","benz"};

The list which comes from UI is carList {"audi","benz","bmw"}.

Problem here is user will be able to add a new row from application. Suppose if user adds a new row of "audi", then the carList will be like {"audi","benz","bmw","audi"}. In this case the list should be sorted like {"bmw","audi","audi","benz"}.

I have tried below code. It works only for without adding a new row, means {"audi","benz","bmw"}.

That too while it gets sorts only the name("bmw","audi","benz") position is getting changed. I have one more field in Car class which is quantity. quantity will be in same position. This position should also get changed along with name.

final List<String> preOrderedList = Arrays.asList("bmw","audi","benz");

Collections.sort(carList, new Comparator<Car>() {
        public int compare(Car l1, Car l2) {
            if (preOrderedList.contains(l1.getName().trim()) && preOrderedList.contains(l2.getName().trim())) {
                return preOrderedList.indexOf(l1.getName().trim()) - preOrderedList.indexOf(l2.getName().trim());
            }
            if (preOrderedList.contains(l1.getName().trim())) {
                return -1;
            }
            if (preOrderedList.contains(l2.getName().trim())) {
                return 1;
            }
            return l1.getName().trim().toString().compareTo(l2.getName().trim().toString());
        }
    });

I Expect the output as {"bmw","audi","audi","benz"} but my actual output is {"bmw","audi","benz","audi"}.

In what way is the list being sorted if you expect the output to be `{"bmw","audi","audi","benz"}`? — Ben R., Feb 08 '19 at 09:53
Based on the names which get matched with carList and preOrderedList — Developer, Feb 08 '19 at 09:54
I would try TreeMap for which you can provide comparator method. It will keep your data in sorted order as you add more data. — Irmak Cakmak, Feb 08 '19 at 10:05

ZhekaKozlov · Accepted Answer · 2019-02-08T11:09:27.107

2

This can be elegantly solved with guava's Ordering.explicit:

Collections.sort(carList, Ordering.explicit(preOrderedList).onResultOf(new Function<Car, String>() {
    @Override
    public String apply(Car car) {
        return car.getName();
    }
}));

The last version of Guava thas supports Java 6 is Guava 20.0:

<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>20.0</version>
</dependency>

edited Feb 08 '19 at 11:09

answered Feb 08 '19 at 10:06

ZhekaKozlov

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Getting error: The method sort(List, Comparator super T>) in the type Collections is not applicable for the arguments (List, Ordering) – Developer Feb 08 '19 at 10:32
@0991 I edited my answer – ZhekaKozlov Feb 08 '19 at 11:10
not working..order is getting changed. – Developer Feb 11 '19 at 06:09
@0991 What do you mean by "changed"? – ZhekaKozlov Feb 11 '19 at 06:25
Thanks for your answer. – Developer Feb 21 '19 at 11:07

Sort list based on specific order in java

1 Answers1