CODEWITHSUNDEEP
javajava-8
user1692342
user1692342

Reputation: 5237

Java ConcurrentModificationException while editing value inside a list streaming a map

I have a Map<String, ClassA> results.

When I do this, I get a ConcurrentModificationException:

results.entrySet().stream().map((entry) -> {
    ClassA objA = entry.getValue();
    if(objA.getList() != null) {
        objA.getList().forEach(x -> {
            if(x.getAttr() != null && x.getAttr.containsKey(key)) {
                List<String> y = x.getAttr().get(key);
                y.replaceAll(ClassB::transformationFunc);
            }
        });
    }
})

Basically what I am trying to do is if my results, has a value of ClassA, check for each element of the list if there is any Attribute with a given key. If so, replace the values of the key with a given transformation function. 

public static String transformationFunc(String input) {
    try {
        JSONObject inputJson = (JSONObject) jsonParser.parse(input);
        return String.format("%s_%s", inputJson.get(key1), inputJson.get(key2));
    } catch (ParseException e) {
        //log
        //throw
    }
}

Upvotes: 0

Views: 108

Answers (1)

Piotr Wilkin
Piotr Wilkin

Reputation: 3491

Basically, you get a ConcurrentModificationException whenever you modify a collection that you are iterating over.

The only way in which you are allowed to modify a collection that you are iterating over is by explicitly using an Iterator. If you want to do work on a collection while you're iterating over it, you have to do it on a working copy of the collection instead.

Upvotes: 4

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