Remove duplicates (both values) - duplicate values from an ArrayList

Question

I have an ArrayList with the following strings;

 List<String> e = new ArrayList<String>();
 e.add("123");
 e.add("122");
 e.add("125");
 e.add("123");

I want to check the list for duplicates and remove them from the list. In this case my list will only have two values, and in this example it would be the values 122 and 125, and the two 123s will go away.

What will be the best way to this? I was thinking of using a Set, but that will only remove one of the duplicates.

Answer 1

In Java 8 you can do:

e.removeIf(s -> Collections.frequency(e, s) > 1);

If !Java 8 you can create a HashMap<String, Integer>. If the String already appears in the map, increment its key by one, otherwise, add it to the map.

For example:

put("123", 1);

Now let's assume that you have "123" again, you should get the count of the key and add one to it:

put("123", get("aaa") + 1);

Now you can easily iterate on the map and create a new array list with keys that their values are < 2.

References:

• ArrayList#removeIf
• Collections#frequency
• HashMap

Answer 2

You can also use filter in Java 8

e.stream().filter(s -> Collections.frequency(e, s) == 1).collect(Collectors.toList())