How to run a map of runnables in order-CodePudding

I'm trying to make a method that runs a series of steps defined by lambdas. The following code illustrates how I am doing it. However, the steps aren't executed in order. I thought about using LinkedHashMap instead of Map, but the lambda says Target type of a lambda conversion must be an interface.

public class Test {
    static void runSomeStuff(Map<String, CheckedRunnable> actions){
        actions.forEach((name, action) -> {
            System.out.println("Running "   name   "...");
            try {
                action.run();
            } catch (Throwable e) {
                throw new RuntimeException(e);
            }
        });
    }
    public static void main(String[] args) {
        runSomeStuff(Map.of(
                "Step 1", () -> {
                    System.out.println("1");
                },
                "Step 2", () -> {
                    System.out.println("2");
                }
                ));
    }
}

CodePudding user response：

You've not shared CheckedRunnable but if you've declared such that your Map.of works, then you should be able to pass in LinkedHashMap such that the order of actions is preserved:

LinkedHashMap<String,CheckedRunnable> actions = new LinkedHashMap<>();
for (String s : List.of("Step X", "Step A", "Step N"))
    actions.put(s, () -> System.out.println("Executing action: " s));
for (int i = 0 ; i < 20; i  ) {
    final int index = i; 
    actions.put("Item " index, () -> System.out.println("Executing #" index));
}

runSomeStuff(actions);

This should print:

Running Step X...
Executing action: Step X
Running Step A...
Executing action: Step A
Running Step N...
Executing action: Step N
Running Item 0...
Executing #0
...

Note that if runSomeStuff is called with other Map implementations the order won't be the same as insertion.

CodePudding user response：

In this case, as mentioned in the comments, List is a semantically more appropriate mean of storing the data because you're not accessing values through their keys, but simply iterating over the map entries.

Instead of using a map in order to fuse the two attributes together the intuitive and maintainable way of structure the data would be to define a custom object. Since Java 16 records it might be literally done with a single line of code.

record Action(String name, Runnable task) {}

List<Action> actions = List.of(
    new Action("Step 1", () -> System.out.println(1)),
    new Action("Step 2", () -> System.out.println(2))
);

But if you're convinced that you need a Map, in case if these tasks are as simple as you've described, you can generate using a plain index-based loop or a stream.

final int actionCount = 3;
        
Map<String, CheckedRunnable> actionByStepName = IntStream.rangeClosed(1, actionCount)
    .boxed()
    .collect(Collectors.toMap(
        i -> "Step "   i,
        i -> () -> System.out.println(i),
        (left, right) -> {
            throw new AssertionError("duplicated keys are not expected");
        },
        LinkedHashMap::new
    ));