Passing Function as an Argument to another Function inside another Class

Question

I want to pass a function as an argument to another function inside another class to execute it and return its return value. Following sample code shows what I want to do. Can you please help me how can I achieve this?

MyClass myClass = new MyClass();
myClass.myFunction( executeFunction( "name", 123 ) );

public long executeFunction( String a, Integer b ) {
    //do something
    return 321;
}

/* inside MyClass */
public <RetTyp> myFunction( /*accept any function as a parameter with RetTyp as a return data type*/) {
   /*execute method coming in the argument and return its return value*/
}

you can create a global function so you can access it from all classes . I think this will make thinks easier — YourHelper, Nov 03 '20 at 19:22
[this can help you](https://stackoverflow.com/questions/4685563/how-to-pass-a-function-as-a-parameter-in-java) — Swapnil Padaya, Nov 03 '20 at 19:32

score 0 · Answer 1 · answered Nov 03 '20 at 19:25

public static class MyTestClass {
    public void main() {
        MyClass myClass = new MyClass();
        myClass.myFunction(this::executeFunction);
    }

    public long executeFunction(String a, Integer b) {
        //do something
        return 321;
    }
}

public static class MyClass<T> {
    public T myFunction(MyFunctionInterface<T> func) {
        return func.run("", 10);
    }

    public interface MyFunctionInterface<T> {
        T run(String a, Integer b);
    }
}

You mean like this? You will always need an interface for this (With the same signature as your method you want to pass)

myClass.myFunction(this::executeFunction); here you should also pass two arguments for executeFunction that are String, Integer — Agha Salman, Nov 03 '20 at 19:28

score 0 · Answer 2 · answered Nov 03 '20 at 19:58

You may define your own functional interface or use BiFunction<T, U, R>:

import java.util.*;
import java.util.function.*;

public class MyClass {

    @FunctionalInterface
    static interface MyFunction<R, T1, T2> {
        R apply(T1 arg1, T2 arg2);
    }
    // static
    public static <R, T1, T2> R myFunction(MyFunction<R, T1, T2> function, T1 arg1, T2 arg2) {
        return function.apply(arg1, arg2);
    }

    // instance
    public  <T1, T2, R> R myBiFunction(BiFunction<T1, T2, R> function, T1 arg1, T2 arg2) {
        return function.apply(arg1, arg2);
    }
    public static long executeFunction(String a, Integer b) {
        System.out.println(a + ", b=" + b);
        return 123L * a.length() * b;
    }

    public static void main(String args[]) {
        System.out.println(myFunction(MyClass::executeFunction, "guess", 100));
        
        System.out.println(myFunction((List<String> a, String b) -> a.indexOf(b), Arrays.asList("abc", "def", "xyz"), "opq"));
        System.out.println(new MyClass().myBiFunction(MyClass::executeFunction, "bi", 999));
    }
}

Output of sample:

guess, b=100
61500
-1
bi, b=999
245754

Passing Function as an Argument to another Function inside another Class

2 Answers2