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Question

Context: https://www.reddit.com/r/dailyprogrammer/comments/4wqzph/20160808_challenge_278_easymed_weave_insert_part_1/

Full Code: http://pastebin.com/UghV3xdT

I have 2 practically identical methods that can only different by one if-statement: if (k % 3 != 1) and if(k % 2 == 0) .

int k = 0;
while(k<50){
    if(k % 3 != 1){ // OR if(k % 2 == 0)
        // Code logic goes here
    k++;
    }
}

The use of each cases is determined by the length of an Array which means the specific case only has to be determined 1 time. 'k' represents the index of another array and 50 is the length of this Array.

I could write something like if(foo > 1 ? k % 3 != 1 : k % 2 == 0) but that requires the program to do the action every time the loop runs.

In a way I would like a sort of updating boolean. Is there any way to do this, or is this the downside of pass-by-value? Should I keep two seperate methods or am I better of with using the ternary operator?

In essence I'm looking for a type that contains the expression rather than the value.

Answer 1

In Java 8 there is nice functional interface called IntPredicate . If you combine it with lambda expressions, you can achieve your goal with no duplication, extra code or any slow downs:

public final class Example {
    public static void main(String[] args) {
        //Instead of randomly choosing the predicate, use your condition here
        Random random = new Random();
        IntPredicate intPredicate = random.nextBoolean() ? i -> i % 2 == 0 : i -> i % 3 != 1;

        int k = 0;
        while(k<50){
            /*
             *At this point the predicate is either k%2==0 or k%3!=1,
             * depending on which lambda you assigned earlier.
             */
            if(intPredicate.test(k)){ 
                // Code logic goes here
                k++;
            }
        }
    }
}

PS: Please not that I use the random boolean value to switch between the predicates, but you can use whatever condition you have

Answer 2

You can create two different classes that have the same function and then use one of it. For example, out of the loop:

class A{ bool calc(int n){return n%3 != 1} }
class B{ bool calc(int n){return n%2 == 0} }
Object x = (foo > 1 ? new A():new B());

Then you can use in the loop only x.calc(k) .

Answer 3

I could not see any way to simplify the logic of your ternary expression in a clever way. But if you place the logical check outside the while loop over k , then you will only have to make the check once:

int k = 0;

if (foo > 1) {
    while (k < 50) {
        if (k % 3 != 1) {
            // code logic goes here
        }
        k++;
    }
}
else {
    while (k < 50) {
        if (k % 2 == 0) {
            // code logic goes here
        }
        k++;
    }
}

This isn't beautiful code, but it frees you from having to use a ternary expression in each iteration of the loop.

Answer 4

Java 8 allows many variants:

IntConsumer businessLogic = (k) -> { ... };

Or make a method and use ::businessLogic .

if (foo) {
    IntStream.range(0, 50)
        .filter(k % 3 != 1)
        .forEach(businessLogic);
} else {
    IntStream.range(0, 50)
        .filter(k % 2 == 0)
        .forEach(businessLogic);
}

Purely a matter of taste, but I like to see the hard numeric constants together. Of course one may write:

To have a loop without condition for the test:

IntStream is = IntStream.range(0, 50);
is = ... ? is.filter(k % 3 != 1) : is.filter(k % 2 == 0);
is.forEach(businessLogic); // Only now one iterates.