CODEWITHSUNDEEP
javaarraylist
Newbie
Newbie

Reputation: 146

Adding into array list

I am a Java newbie.. But I am sure I can get this done much efficient manner.

The purpose of this method is to add the product with an unique Id. If I the product as duplicate I should thrown an exception. Well, this sequence is not for multi-threaded environment.

public void addProduct(Product product)
        throws ProductAlreadyExistsException {
    product.id = ++nextId;
    this.id = product.id;

    Iterator<Product> it = allProducts.iterator();
    Product p= null;

    boolean flag= false;
    if (!allProducts.isEmpty()) {
        while(it.hasNext()){
            p= it.next();
            if ( p.getName() == product.getName())
                throw new ProductAlreadyExistsException(p.getName());
            else
                flag = true;
        }

    }
    else
        allProducts.add(product.id-1, product);

    if(flag){
        allProducts.add(product.id-1, product);
    }
}

What I want is something like this.

    for (Product p : allProducts) {
        if (p.getName() ==  product.getName() ) {
            throw new ProductAlreadyExistsException(p.getName());
        }
            allProducts.add(p);
        }
}

This does not work. Thanks for guiding me..

Upvotes: 1

Views: 148

Answers (3)

SeriousBob
SeriousBob

Reputation: 133

Makoto's answer is a simple way to make sure that an object is unique in a List.

Additionally you need to make sure to implement the equals(Object obj) method in the class of the objects, you want to add to the list. The List.contains() method calls equals(yourObject) on each object it contains and returns true, as soon as equals(yourObject) returns true for any of the objects in the List.

Here you can see a good implementation of equals(Object obj) you could use in your Product class.

public class Product {
    //Other methods here
    public boolean equals(Object obj) {
        if(this == obj) 
            return true;
        if(obj == null)
            return false;
        if(this.getClass() != obj.getClass())
            return false;
        Product product = (Product)obj;
        boolean result = true;
        //Compare fields of this with fields of product and set result
        return result;
    }
}

Upvotes: 0

sha1
sha1

Reputation: 143

In Java, you use s1.equals(s2) method to identify if two strings are equal.

 if ( p.getName() == product.getName()) // This will always return false, because references are compared here

What you should do is: 

if ( p.getName().equals(product.getName()) )

NOTE: I'm assuming that getName() returns a string.

Upvotes: 3

Makoto
Makoto

Reputation: 106389

In general, there's no guarantee granted that a List of any kind will contain only unique elements, but I would imagine you don't have to go through the process of creating an Iterator.

Merely making use of List.contains() is sufficient - if the list doesn't contain the element, add it in, otherwise, throw the exception*.

public void addProduct(Product theProduct) throws ProductAlreadyExistsException {
    if(allProducts.contains(theProduct)) {
        throw new ProductAlreadyExistsException("Not unique!");
    }
    allProducts.add(theProduct);
}

*: Throwing the exception is a bit silly IMO. That should only be reserved for truly exceptional behavior. You're probably better off with a Set of some sort instead.

Upvotes: 3

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