Question

My Arraylist contains 9 persons. Each person has a name value of type String, an age value of type int and a value of type Enum (TV, SMARTPHONE, CAR). I must create implement a method that will find the name according to the product name.
If arrayListName contains SMARTPHONE, return all names with a smartphone.

public void showByProduct(Product SMARTPHONE) {



    public void showByProductName(Product SMARTPHONE) {

            if (arrayListName.contains(SMARTPHONE))

                System.out.println("found"+nameofowner);
            else {
                System.out.println("not found");
            }
        }

Answer 1

You would need to iterate over your List, and for each Person, check if it’s product field has the value of the one that you passed in the method.

Additionally, you would need to have one more List local to your method, in which you would add the Person which matches the Product Name, and then at the end return that List.

public List<Person> showByProductName(Product product) {

    List<Person> localList = new ArrayList<Person>();

    for (Person person: persons) {   // persons is the original List.
        if (person.getProduct() == product) {
            localList.add(person);
        }
    }

    return localList;
}

And the place where you call this method, store the return value in a List reference: –

List<Person> result = showByProductName(Product.SMARTPHONE);
System.out.println(result);

Note that, you can compare two enum values using ==. As an enum is a singleton.

P.S: – Don’t have your parameter name as SMARTPHONE. It’s an enum value. And also as per Java Naming Convention, variables name should start with lowercase alphabets, and follow camelCasing thereon.