Java 8 - Nested if inside a loop

Question

So I have a list and for each item in the list I have to "do something" based on each list element.

The list consists of codes and there are a total of 5 codes. The list may contain any or all codes.

So far I've used the forEach and i've written the if conditions inside it as below -

List<Category> categories = getCategories();

categories.stream().forEach(category -> {
            if(category.equals(Category.A)) {
                // do something
            } else if(category.equals(Category.B)) {
                // do something
            } else if(category.equals(Category.C)) {
                // do something
            } else if(category.equals(Category.D)) {
                // do something
            } else if(category.equals(Category.E)) {
                // do something
            }
        });

I'm looking at refactoring this. Can someone please look at how better this can be done?

You could put `// do something` inside a method `void doSomething()` that every Category overwrites and then simply write `category.doSomething()`. — luk2302, Nov 02 '17 at 12:57
Create a loopkup table. See [this question](https://stackoverflow.com/questions/4480334/how-to-call-a-method-stored-in-a-hashmap-java) for info. — pritaeas, Nov 02 '17 at 12:59
The stream creation is not necessary here, either. The Collection interface has a forEach method — Felix S, Nov 03 '17 at 09:19

Basti · Answer 1 · 2017-11-02T13:14:37.110

1

The only thing I would improve is to use a switch-statement:

switch(category){    
   case Category.A:
        // do Something
   break;
}

As mentionend by luk2302 this will only work if Category is an enum.

edited Nov 02 '17 at 13:14

answered Nov 02 '17 at 12:58

Basti

517
4
19

1

what if `Category` is simply a regular class, not an enum!? – luk2302 Nov 02 '17 at 12:59
Then it won't work I guess. The Author didn't really provide this info. It's worth a try. – Basti Nov 02 '17 at 13:01
Category is an Enum so this will work. I was going to use either the nested if or switch but the reason I asked this was to see if there was any possibility of using lambda functions to do this. – Nov 03 '17 at 09:15

score 1 · Answer 2 · answered Nov 02 '17 at 16:19

1

You can add a doSomething method to the Category class and simply call it in the .forEach.

For example:

public class Category {

    // any other methods/variable/constructors

    public void doSomething() {
        //do something
    }
}

Then you can call it like this:

categories.stream().forEach(Category::doSomething);

If the // do something has not a common behaviour, you can move the if part inside the doSomething method.

answered Nov 02 '17 at 16:19

araknoid

3,065
5
33
35

Category is an enum. I could write the login in the enum class but I would want to keep the logic separate. This would've definitely been my implementation if it was a class. thanks! – Nov 03 '17 at 09:19

score 0 · Accepted Answer · answered Nov 02 '17 at 14:14

At first, do not use multiline lambdas and create new method (with switch):

private void doSomethingBasedOnCategory(Category category) {
    switch(category) {
        case A: // do something
                break;
        case B: // do something
                break;
        case C: // do something
                break;
        case D: // do something
                break;
        case E: // do something
                break;
    }
}

Then use it in your lambda:

getCategories()
    .stream()
    .forEach(category -> doSomethingBasedOnCategory(category);

Another way is to create static map prefilled with keys (which will be Category.X) and values (which will be functions ready to use)

Could also use method reference `this::doSomethingBasedOnCategory` — Lino, Nov 02 '17 at 14:54

Java 8 - Nested if inside a loop

3 Answers3