Task

Create a list of ten functions, in the simplest manner possible   (anonymous functions are encouraged),   such that the function at index    i     (you may choose to start     i     from either    0    or    1),    when run, should return the square of the index,   that is,     i  2.

Display the result of running any but the last function, to demonstrate that the function indeed remembers its value.



Goal

Demonstrate how to create a series of independent closures based on the same template but maintain separate copies of the variable closed over.

In imperative languages, one would generally use a loop with a mutable counter variable.

For each function to maintain the correct number, it has to capture the value of the variable at the time it was created, rather than just a reference to the variable, which would have a different value by the time the function was run.

See also: Multiple distinct objects

import java.util.function.Supplier;
import java.util.ArrayList;
 
public class ValueCapture {
    public static void main(String[] args) {
	ArrayList<Supplier<Integer>> funcs = new ArrayList<>();
	for (int i = 0; i < 10; i++) {
	    int j = i;
	    funcs.add(() -> j * j);
	}
 
	Supplier<Integer> foo = funcs.get(3);
	System.out.println(foo.get()); // prints "9"
    }
}