Iterate through ArrayList of instance's variable

Question

I want to know how to iterate through the following Arraylist.

public class FruitHandler {

    private ArrayList<Fruits> fruit;
    private ArrayList<Integer> fruitUID= new ArrayList<>();

    public static FruitHandler getInstance() {
            return instance;
    }

    public void addFruit(Fruit fruit) {
        this.fruitUID.add(fruit.getfruitUID());
        this.fruit.add(fruit);
    }
}

What I want to do is to iterate through the fruitUID and return the instance of that fruit class that is stored in ArrayList<Fruits> fruit which matches my given UID.

Example, I have an fruitUID = 10, I want to have the reference of the instance of the fruit class that is stored in ArrayList<Fruits> fruit which have its fruitUID = 10.

Jason · Accepted Answer · 2019-02-22 04:28:08Z

5

If you want to retrieve a Fruit instance given a fruitUID then you probably want a Map<Integer, Fruit>.

You could also just have a list of Fruit instances and use a stream and a filter to find just the single instance with a specified fruitUID.

If you absolutely must use two lists, then you need find the index of the specified fruitUID and extract the Fruit from the other list at the same index.

Edit: If you want to use a map:

private Map<Integer, Fruits> fruits = new HashMap<>();

public void addFruit(Fruit fruit) {
    fruits.put(fruit.getfruitUID(), fruit);
}

public Fruit findFruit(Integer fruitUID) {
    return fruits.get(fruitUID);
}

edited Feb 22, 2019 at 4:28

answered Feb 22, 2019 at 4:24

Jason

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2 Comments

Emily Wong Over a year ago

I think I'm overthinking much, how to iterate through the map of fruits from external class? or no need to iterate? i just call findFruit and thats all.

CryptoFool Over a year ago

@Emily, that's what's great about a Map. No iterating. It takes you right to the Fruit you're looking for. - I highly recommend you study up a bit on data structures, especially HashMaps. They're one of the cornerstones of computing...a concept of optimizing data lookups that we all use every day.

Bernard Nongpoh · Accepted Answer · 2019-02-22 05:47:06Z

The solution point out by @Jason will make your problem much easier, but if you are in hurry and consider using a quick solution you can have the following code (not good in term of performance

public class FruitHandler {

    private ArrayList<Fruits> fruit;
    private ArrayList<Integer> fruitUID= new ArrayList<>();

    public static FruitHandler getInstance() {
            return instance;
    }
    public void addFruit(Fruit fruit) {
        this.fruitUID.add(fruit.getfruitUID());
        this.fruit.add(fruit);
    }
    public Fruit findFruitByFruitUID(Integer fruitUID){
             for(Fruit fr: fruit){
                     if(fr.getfruitUID()==fruitUID){
                      return fr;
                      }
             }
        return null;
         }
}

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