CODEWITHSUNDEEP
javastringloopsarraylistsubstring
SpaceMonk
SpaceMonk

Reputation: 155

why is everything getting removed from my arraylist?

I'm trying to answer this question:

Program the method findIngredients. This method takes in a String called foodInStock, and an ArrayList of Strings called ingredients. The method should return an ArrayList of ingredients that were not found in foodInStock.

for example if:

foodInStock = “tomatopotatocornturkeycarrotstuffing”

ingredients = {“potato”, “corn”, “salt”, “chicken”, “turkey”}

returns {“salt”, “chicken”}

I tried writing some code but for some reason everything is getting removed when I use the above example on my program. Where did my program go wrong?

Here's my code:

public static ArrayList<String> findIngredients(String foodInStock, ArrayList<String> ingredients){
    ArrayList<String> ingredientsNotFound = new ArrayList<String>();
    int i = 0;
    for (; i < ingredients.size(); i++) {
        for (int x = 0; x < foodInStock.length()-(ingredients.get(i).length())+1; x++) {
            if (ingredients.get(i) == foodInStock.substring(x, (x + ingredients.get(i).length()))) {
                ingredients.remove(i);
                i = 0;
                break;
            }
        }
    }
    ingredients = ingredientsNotFound;
    return ingredientsNotFound;
}

Upvotes: 4

Views: 64

Answers (1)

Ben P.
Ben P.

Reputation: 54194

I think there are two main things to cover here.

First, the way to build the final result. You are currently removing items from the original input; a better strategy is to add items to a new list (partially because it's simpler to think about and partially because you generally don't want to modify a list while iterating over it).

You also are, probably accidentally, overwriting your list with an empty list at the end.

Second, the way to determine whether or not the ingredient is in the string input. Rather than looping over the whole string and inspecting substrings, you can instead use the indexOf() method to see whether or not the string includes the current item.

public static ArrayList<String> findIngredients(String foodInStock, ArrayList<String> ingredients) {
    ArrayList<String> results = new ArrayList<>();
    for (String ingredient : ingredients) {
        if (foodInStock.indexOf(ingredient) == -1) {
            results.add(ingredient);
        }
    }
    return results;
}

Here we initialize a new list for the results. We then loop over every individual ingredient in the input list, and ask whether or not that ingredient is present in the string input. When it is not (indexOf() returns -1), we add it to the results list. At the end, the results contains every ingredient not found.

Upvotes: 5

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