[SOLVED] How to pass NOT operator dynamically

How to pass NOT operator dynamically

I have a Map<MyObject, String> myMap and I want to filter it in two other maps.

What I would like my code to look(pseudo code) something like this.

newMap = filter(myMap, dontApplyNOT);

myMap = filter(myMap, NOT);

public Map<Object, String> filter(... myMap, NOT) {
 return myMap.entrySet().stream().filter(entry -> NOT condition(entry)).collect();
}

For reasons I can not add Equals to the Object nor can I change the data structure.

I am expecting to inverse the condition dynamically so I would not have to duplicate the filtering function.

Solution

Since the choice is simply between "apply !" and "don't apply !", you can use a boolean to represent this choice.

public Map<Object, String> filter(..., boolean invertCondition) {
    return myMap.entrySet().stream()
        .filter(entry -> condition(entry) != invertCondition)
        .collect(...);
}

Note the expression condition(entry) != invertCondition. This is the same as condition(entry) if invertCondition is false, and is the same as !condition(entry) if invertCondition is true.