Decrease two custom objects values using reduce operation

Question

I have a custom object like the following one.

public class Count {
    private int words;
    private int characters;
    //getters & setters && all args constructor

    void Count decrease(Count other) {
       this.words -= other.words;
       this.characters -= other.characters; 
       return this;
    }
}

I want to achieve the next result, eg:

Count book1 = new Count(10, 35);

Count book2 = new Count(6, 10);

the result would be: Count result = Count(4, 25) -> ([10-6], [35-10])

I tried this solution but it didn't work.

Stream.of(book1, book2).reduce(new CountData(), CountData::decrease)

It's possible to achieve this result using reduce operation or another stream operation from java >=8?

Answer 1

The following ad hoc solution uses a single-element stream of book2 to be subtracted from a seed initialized with book1 values:

Count reduced = Stream.of(book2)
    .reduce(new Count(book1.getWords(), book1.getCharacters()), Count::decrease);

Here value of book1 is not affected.

However, for this specific case this can be done without Stream API:

Count reduced = new Count(book1.getWords(), book1.getCharacters())
        .decrease(book2);