How to invoke different methods from parameters in Java?

Question

Assume that I have a method A and B from a class:

List<String> A(int start, int size);
List<String> B(int start, int size);

Now, I have another function that might use A or B. But before invoking them, I'll do some logic first:

void C() {
 // lots of logic here
 invoke A or B
 // lots of logic here 
}

I want to pass method A or B as parameter of C, something like:

void C(Function<> function) {
 // lots of logic here
 invoke function (A or B)
 // lots of logic here 
}

However, I noticed that the Function class in Java can only accept one parameter (method A or B both have two parameters). Is there a workaround on this? (I don't want to change the method A or B signatures).

Wow, thanks. BTW, what if method A and B has different return types (List<String> vs List<Integer>) ? Does this still work? — injoy
– injoy, Commented Aug 1, 2018 at 23:45
Use Lambdas. The only change would be function A and function B would be an implementation of an abstract function — Nandish A
– Nandish A, Commented Aug 1, 2018 at 23:45

Ousmane D. · Accepted Answer · 2018-08-01 23:46:10Z

4

BiFunction represents a function that accepts two arguments and produces a result, so you may want to look into that here.

edited Aug 1, 2018 at 23:46

answered Aug 1, 2018 at 23:45

Ousmane D.

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2 Comments

injoy Over a year ago

Thanks, BTW, what if method A and B has different return types (List<String> vs List<Integer>) ? Does this still work?

Ousmane D. Over a year ago

@injoy try generalising your method to <T> void C(BiFunction<Integer, Integer, List<T>> function) {...}?

Soner from The Ottoman Empire · Accepted Answer · 2018-08-01 23:50:22Z

0

You can use and write your own functional interface by lambda expression. I illustrate here,

interface MyInterface<T> {
    List<T> f(int start, int size);
}

class Example {
    List<String> A(int start, int size) {
        return new ArrayList<String>();
    }

    List<Integer> B(int start, int size) {
        return new ArrayList<Integer>();
    }

    void C(MyInterface function) {

    }

    public static void main(String[] args) {
        Example e = new Example();
        MyInterface<String> methodForA = (x,y) -> e.A(1,2);
        MyInterface<Integer> methodForB = (x,y) -> e.B(1,2);

        e.C(methodForA);
        e.C(methodForB);
    }
}

answered Aug 1, 2018 at 23:50

Soner from The Ottoman Empire

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2 Comments

vandench Over a year ago

Why not just use a method reference instead of a lambda?

Soner from The Ottoman Empire Over a year ago

@vandench I don't have enough knowledge yet about method references

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