CODEWITHSUNDEEP
javadata-structuresiterator
Niminim
Niminim

Reputation: 678

Java - return a reference to a specific place in a linkedlist with list iterator

I have a Portfolio class that also has linkedlist of Investment class (example - Google is an instance of Investment), each investment has a trade history (another linked list) with data for each trade.

When the user want to make a trade (buy google stocks for 5K) I need to find if the investment (in google) already exists in the investmentsList. If it doesn't - add new investment (and add the trade for its trade history), If it does - just add another link to google's tradeHistory linkedlist.

The problem - I need findInvestment method to return a reference to google (investment instance) from the investmentList so I can update its trade history.The method returns a listIterator rather than a reference to a location in investmentList(should be Investment Class). How should I correct findInvestment? (found=iter is wrong)

public class Portfolio {


private LinkedList<Investment> investmentsList;

public Portfolio() {
    investmentsList = new LinkedList<Investment>();
}

public void addInvestment(String symbol, double money){

    Investment invest = findInvestment(symbol);
    if (invest == null) {
        System.out.println("symbol does not exist");
        getInvestmentsList().add(new Investment(symbol,money));
        System.out.println("New invetment has been added to your portfolio - " +symbol);
    } else {
        invest.addTrade(symbol,money);
        System.out.println("A new trade has been added to the current investment - " + symbol);

    }
}

public Investment findInvestment(String symbol){

    Investment found = null;
    ListIterator<Investment> iter = investmentsList.listIterator();


    while (iter.hasNext()) {

       if (iter.next().getSymbol().equals(symbol)) {
            found = iter;
            return found;
            System.out.println("Found the symbol");
        }
    }

    return found;
}

Upvotes: 6

Views: 387

Answers (3)

GhostCat
GhostCat

Reputation: 140553

You already answered your question in your code!

   if (iter.next().getSymbol().equals(symbol)) {
        found = iter;

See?

You are calling iter.next() which gives you exactly what you are looking for! So, you simple have to rework your code within the loop like:

Investment currentInvestment = iter.next();
if (currentInvestment.get...) {
  found = currentInvestment;
  println...
  return found;
}

And for the future: please read the javadoc of the classes you are dealing with. They typically tell you everything you need to know! Hint no. 2: there is no point in having a println after the return statement.

And I feel inclined to say: have some experienced people review your code. It is not buggy; but there are quite some things that could be improved; like your usage of double for currency (which is always a horrible idea); or the fact that your "model" of an investment ... boils down to a string denoting its "symbol". That is awfully "low-level".

Upvotes: 2

Joop Eggen
Joop Eggen

Reputation: 109593

Simply hold an Investment - or in java 8 Optional<Investment>

Instead of the linked list:

private Map<String, Investment> investmentsBySymbol;

public Investment findInvestment(String symbol){
    Investment found = investmentsList.get(symbol);
    return found;
}

Also BigDecimal is a better choice than double as

new BigDecimal("3.10");

has a precision of 2, and doubles are always inprecise.

Upvotes: 3

Murat Karag&#246;z
Murat Karag&#246;z

Reputation: 37604

Use it like this

 while (iter.hasNext()) {

   if ((found = iter.next()).getSymbol().equals(symbol)) {
        System.out.println("Found the symbol");
        return found;

    }
}

Upvotes: 2

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