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javamultithreadingconcurrency

Java CopyOnWriteArrayList add element if not exists already

I have an CopyOnWriteArrayList as my code should be thread safe. List friuts = new CopyOnWriteArrayList<>();

I don't want to have duplicate friuts in list I cannot use Set as I want to have insertion order as well. I have written this code

public boolean add(String friut) {
    synchronized (friuts) {
        if (friuts.contains(friut)) {
            return false;
        }
        friuts.add(friut);
    }
    return true;
}

As I know is CopyOnWriteArrayList already concurrent. So adding CopyOnWriteArrayList.add within synchronized block doesn't seems to be a good idea to me. Is there any other better solution?

Solution

  • Use the addIfAbsent() method:

    CopyOnWriteArrayList<String> fruits = new CopyOnWriteArrayList<>();

public boolean add(String fruit) {
    fruits.addIfAbsent(fruit);
}