Java 8, how can I implement a switch statement using streams?

Question

I have a text file imgui.ini containing:

[Debug]
Pos=7,79
Size=507,392
Collapsed=0

[ImGui Demo]
Pos=320,5
Size=550,680
Collapsed=0

Answer 1

Focusing on the question "is there a way to simulate switch statement behavior", I think the answer is that you could, with a little effort. I asked myself that a couple of years ago, and did the following as an exercise (and then never used it again):

private static  Predicate testAndConsume(Predicate pred, Consumer cons) {
    return t -> {
        boolean result = pred.test(t);
        if (result) cons.accept(t);
        return result;
    };
}

public static class SwitchConsumer {
    Predicate conditionalConsumer;
    private SwitchConsumer(Predicate pred) {
        conditionalConsumer = pred;
    }

    public static  SwitchConsumer inCase(Predicate pred, Consumer cons) {
        return new SwitchConsumer<>(testAndConsume(pred, cons));
    }

    public SwitchConsumer elseIf(Predicate pred, Consumer cons) {
        return new SwitchConsumer<>(conditionalConsumer.or(testAndConsume(pred,cons)));
    }

    public Consumer elseDefault(Consumer cons) {
        return testAndConsume(conditionalConsumer.negate(),cons)::test;   // ::test converts Predicate to Consumer
    }
}

testAndConsume composes a Predicate and a Consumer, creating a Predicate that returns the same value but calls the Consumer as a side-effect if the value is true. That becomes the basis for each "case" in the "switch". Each "case" is strung together by Predicate.or(), which provides the short-circuiting "else-if" nature of the switch. Finally, the composed Predicate is turned into a Consumer by adding ::test to the Predicate.

Applying it to your code snippet, it looks like this:

    Stream.of("Pos=320,5", "Size=550,680", "Collapsed=0")
            .map(s -> s.split("="))
            .forEach(SwitchConsumer.
                    inCase(arr -> "Pos".equals(arr[0]), arr -> settings.pos = arr[1])
                    .elseIf(arr -> "Size".equals(arr[0]), arr -> settings.size = arr[1])
                    .elseIf(arr -> "Collapsed".equals(arr[0]), arr -> settings.collapsed = arr[1])
                    .elseDefault(arr -> {}));

That's about as switch-ish as it can get without an actual switch in a Consumer body.