CODEWITHSUNDEEP
javaarraysswingjakarta-eeset
Mellon
Mellon

Reputation: 38872

Remove duplicated elements in array by using Set in my case

I have a Array of object, since I am using a 3rd party library, the array is got by calling one method from the library, I am not able to access the MyObject class.

//I have no access to MyObject class, I am sure the objects contain duplicated elements.
MyObject[] objects = SOME_LIB_CLASS.getObjects(); 
System.out.println("length is "+ objects.length); //length is 6

I try to remove duplicated elements in objects, I use Set:

Set<MyObject>  objectSet = new HashSet<MyObject>(Arrays.asList(objects));
System.out.println("length is "+ objectSet.size()); //length is 6 still

But the objectSet still contains duplicated elements, why & how to solve my problem without iterate through the array?

Upvotes: 1

Views: 1324

Answers (4)

javid piprani
javid piprani

Reputation: 1965

Hope below code help you 

            ArrayList al = new ArrayList();
            al.add("hello");
            al.add("hi");
            al.add("hello");
            al.add("dadsa");
            al.add("hello");

            // add elements to al, including duplicates
            HashSet hs = new HashSet();
            hs.addAll(al);
            al.clear();
            al.addAll(hs);

            for(int i=0; i<al.size(); i++)
            {
                Log.i("element ", al.get(i).toString());

            }

It will remove all duplicate values from arraylist

Upvotes: 0

Ren&#233; Link
Ren&#233; Link

Reputation: 51423

If the set still contains "duplicate" elements than the equals method of your objects does not what you expect it to do.

Duplicates in a HashSet are determined by the equals implementation.

If you can not change the implementation of MyObject.equals()( because you don't have the source code - it is a library class), I recommend to use a TreeSet and provide a special comparator.

For example

public class Main {

    public static class MyObject {

        public int value;

        @Override
        public String toString() {
            return "MyObject [value=" + value + "]";
        }

    }

    public static void main(String str[]) throws IOException {
        Set<MyObject> myObjects = new TreeSet<MyObject>(
                new Comparator<MyObject>() {

                    public int compare(MyObject object1, MyObject object2) {
                        return object1.value - object2.value;
                    }
                });

        addMyObjects(myObjects);
        addMyObjects(myObjects); // try to add the duplicates

        System.out.println(myObjects);
    }

    private static void addMyObjects(Set<MyObject> set){
        for (int i = 0; i < 5; i++) {
            MyObject myObject = new MyObject();
            myObject.value = i;
            set.add(myObject);
        }
    }
}

Upvotes: 3

codingenious
codingenious

Reputation: 8653

Can you try to print hashcode of the objects, I think those objects are not same but have same values for there fields. and if MyObject is your class, override equals and hascode method to make set working.

Upvotes: 0

Ezzored
Ezzored

Reputation: 925

It contains duplicated entries, because MyObject doesn't overwrite equals and hashcode. If you can't access the class, then you have to iterate over the array, and check for differences manually.

Upvotes: 0

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