Java – how to short circuit when calculating duplicate values between two lists?

I have 2 lists. I need to calculate / check the duplicate elements in list a that match the elements in List B in the fastest way

For example, if list a is ["a", "B", "C"], then list B is ["X", "a", "C", "C"], my counter should be 2, because there are two duplicate elements ("B" and "C") in B. since it is a boolean method, it should return true whenever there is any repetition of a in B

I'm avoiding cascading loops and even trying to use streams Although the following code works, I'm still not sure about its design That's how I do it now:

class MyPojo {
    int value; String str;
    MyPojo(int value) { this.value = value; };
    /* getters & setters*/ 
}

public static boolean hasDuplicates() {
    List<Integer> forbiddenValues = Arrays.asList(1,2,3);
    List<MyPojo> pojoList = Arrays.asList(new MyPojo(0),new MyPojo(2),new MyPojo(3),new MyPojo(4));

    for ( Integer value : forbiddenValues) {
        long count = pojoList.stream()
            .filter( pojoElement -> pojoElement.getValue() == value)
            .count();
        // returns true if in a single iteration count is greater than 1
        if ( count > 1) {
           return true;
        }
    }
    return false;
}

Solution

This will help you Let me know if you have any questions You can also use parallel streams if necessary

Using the stream API

public static boolean hasDuplicates() {
        List<Integer> forbiddenValues = Arrays.asList(1,3);

        List<MyPojo> pojoList = Arrays.asList(new MyPojo(0),new MyPojo(4));


        long count = pojoList.stream()
                .filter(pojo -> forbiddenValues.contains(pojo.getValue()))
                .map(MyPojo::getValue)
                .collect(Collectors.groupingBy(value -> value))
                .values()
                .stream()
                .filter(values -> values.size() > 1)
                .count();

        return count > 1;
    }

No streams

public static boolean hasDuplicates() {
        List<Integer> forbiddenValues = Arrays.asList(1,new MyPojo(4));


        Map<Integer,Integer> counts = new HashMap<>();

        for(int forbidden : forbiddenValues){
            counts.put(forbidden,0);
        }

        for(MyPojo myPojo : pojoList){
            if(counts.containsKey(myPojo.getValue())){
                int count = counts.get(myPojo.getValue());

                if(count == 1){
                    return true;
                }

                counts.put(myPojo.getValue(),count + 1);
            }
        }

        return false;
    }