Is there a way to use a method as an input variable for another method in Java?

Question

I attempted to create a method which calculates the sum of the values of another method in the same way the capital sigma notation does in math. I wanted it to use successive natural numbers as input variables for the function and use recursion to sum it all up. However, as I wanted to create a method for general summation, I am not sure how to assign another (single variable) method as an input variable.

I thought of something like this:

    public static int sum(int lowerbound, int upperbound, function(int x)){
        int partialsum = 0;
        for (int i = lowerbound; i <= upperbound; i++){
        partialsum = partialsum + function(i);
        }
        return partialsum;
    }

Is it possible?

Elliott Frisch · Accepted Answer · 2020-01-05 00:30:58Z

3

Yes, it is possible; but you would need to pass a IntFunction (Java is not JavaScript). Like,

public static int sum(int lowerbound, int upperbound, IntFunction<Integer> function) {
    int partialsum = 0;
    for (int i = lowerbound; i <= upperbound; i++) {
        partialsum = partialsum + function.apply(i);
    }
    return partialsum;
}

And then to use it, something like

public static void main(String[] args) {
    System.out.println(sum(1, 10, a -> a));
}

Which outputs

It isn't clear what result you would expect (or what function you intended to pass).

answered Jan 5, 2020 at 0:30

Elliott Frisch

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2 Comments

gegorg Over a year ago

I am new to programming and want to incorporate it into solving my math homework. Right now it's just practice for me. Originally I tried to write a program which approximates the Kempner Series and I then I wanted to sum up some probabilities from Bernoulli trials.

Bohemian Over a year ago

IntUnaryOperator Is probably a better choice

Carcigenicate · Accepted Answer · 2020-01-05 00:38:58Z

0

You pass in a IntUnaryOperator

public static int sum(int lowerbound, int upperbound, IntUnaryOperator func) { 
    ...
    partialsum += func.applyAsInt(i);

Then, either pass a method in, or use a lambda:

sum(1, 2, n -> n * 2)

edited Jan 5, 2020 at 0:38

answered Jan 5, 2020 at 0:31

Carcigenicate

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