Why can't I access the Stock objects o1 and o2 properties such as name?

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I am trying to compare the 2 objects from line 49 but I can't get to their members. ex name; I see that class Stock extends hashmap and that the constructor takes as argument some variables which in turn are put in a map. Is that object a map? Am I supposed to compare the values of o1 and o2? and then rearrange them in the list? I can't find anything relevant on the internet about custom classes extending hashmap and their behaviour. What is going on with this task?

1. In the sort method, write a comparator for Stock:
1.1. Sort first by name in alphabetical order
1.2. Sort second by date without accounting for hours, minutes, and seconds (with the newest on top), and then by profit from positive to negative

... open 125.64 and last 126.74. Here the gain is 126.74-125.64
... open 125.64 and last 123.43. Here the gain is 123.43-125.64

2. Take a look at the *Format classes and fix the IllegalArgumentException.
Hint: it's one line.

Example output:

Fake Apple Inc.   AAPL | 16-03-2027 open 125.64 and last 123.43
Fake Applied Materials, Inc.   AMAT | 15-01-1983 change 0.26

Requirements:

No exceptions should occur while the program is running.
The program should display data on the screen.
The sort method must correctly sort the passed list according to the task conditions.
The Solution.Stock class must be public.

package com.codegym.task.task24.task2412; import java.text.ChoiceFormat; import java.text.Format; import java.text.MessageFormat; import java.text.SimpleDateFormat; import java.util.*; /* Knowledge is power! */ public class Solution { public static void main(String[] args) { List<Stock> stocks = getStocks(); sort(stocks); Date actualDate = new Date(); printStocks(stocks, actualDate); } public static void printStocks(List<Stock> stocks, Date actualDate) { SimpleDateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy"); double[] filelimits = {0d, actualDate.getTime()}; String[] filepart = {"closed {4}", "open {2} and last {3}"}; ChoiceFormat fileform = new ChoiceFormat(filelimits, filepart); Format[] testFormats = {null, dateFormat, fileform}; MessageFormat pattform = new MessageFormat("{0} {1} | {5} {6}"); pattform.setFormats(testFormats); for (Stock stock : stocks) { String name = ((String) stock.get("name")); String symbol = (String) stock.get("symbol"); double open = !stock.containsKey("open") ? 0 : ((double) stock.get("open")); double last = !stock.containsKey("last") ? 0 : ((double) stock.get("last")); double change = !stock.containsKey("change") ? 0 : ((double) stock.get("change")); Date date = (Date) stock.get("date"); Object[] testArgs = {name, symbol, open, last, change, date, date.getTime()}; System.out.println(pattform.format(testArgs)); } } public static void sort(List<Stock> list) { Collections.sort(list, new Comparator<Stock>() { @Override public int compare(Stock o1, Stock o2) { o1.get() return 0; } }); } public static class Stock extends HashMap<String, Object> { public Stock(String name, String symbol, double open, double last) { put("name", name); put("symbol", symbol); put("open", open); put("last", last); put("date", getRandomDate(2020)); } public Stock(String name, String symbol, double change, Date date) { put("name", name); put("symbol", symbol); put("date", date); put("change", change); } } public static List<Stock> getStocks() { List<Stock> stocks = new ArrayList<>(); stocks.add(new Stock("Fake Apple Inc.", "AAPL", 125.64, 123.43)); stocks.add(new Stock("Fake Cisco Systems, Inc.", "CSCO", 25.84, 26.3)); stocks.add(new Stock("Fake Google Inc.", "GOOG", 516.2, 512.6)); stocks.add(new Stock("Fake Intel Corporation", "INTC", 21.36, 21.53)); stocks.add(new Stock("Fake Level 3 Communications, Inc.", "LVLT", 5.55, 5.54)); stocks.add(new Stock("Fake Microsoft Corporation", "MSFT", 29.56, 29.72)); stocks.add(new Stock("Fake Nokia Corporation (ADR)", "NOK", .1, getRandomDate())); stocks.add(new Stock("Fake Oracle Corporation", "ORCL", .15, getRandomDate())); stocks.add(new Stock("Fake Starbucks Corporation", "SBUX", .03, getRandomDate())); stocks.add(new Stock("Fake Yahoo! Inc.", "YHOO", .32, getRandomDate())); stocks.add(new Stock("Fake Applied Materials, Inc.", "AMAT", .26, getRandomDate())); stocks.add(new Stock("Fake Comcast Corporation", "CMCSA", .5, getRandomDate())); stocks.add(new Stock("Fake Sirius Satellite", "SIRI", -.03, getRandomDate())); return stocks; } public static Date getRandomDate() { return getRandomDate(1970); } public static Date getRandomDate(int startYear) { int year = startYear + (int) (Math.random() * 30); int month = (int) (Math.random() * 12); int day = (int) (Math.random() * 28); GregorianCalendar calendar = new GregorianCalendar(year, month, day); return calendar.getTime(); } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

13 April 2021, 14:17

solution

Yes, by extending HashMap the stock class is a HashMap with all the functionality of any other HashMap, with the addition that it has 2 constructors that a HashMap does not have. You can extend Maps, Lists, Trees and various other things to add additional functionality. I commonly extend them just to override the toString() method so I can customize the output when passing to the println() method. The Comparator object is used by the sorting algorithm as the logic to sort the Collection that is passed in as the the first argument: Collections.sort(First_Arg_A_Collctn_To_Be_Sorted, Scnd_Arg_The_Comparator) The Comparator's only job is to provide the logic on how to sort 2 objects, o1 and o2. The sort Algorithm will apply that one piece of logic to sort every single item in the Collection. Here is the logic that you need: 1) compare the first order of sort, which is the 'name' of o1 and o2: (The compare function returns an int) 2) check if the int DOES NOT EQUAL 0, if true then return that int if false 3) compare the second order of sort, which is Date (day month year ONLY) 4) check if that int DOES NOT EQUAL 0, if true then return that int if false 5) compare the last order of sort, which is by profit (last price minus the starting price.. or "change") 6) because this is the last sort order just return the int from compare You see the pattern? You can add as many levels of sort as you want just by repeating the pattern. It is often done in a loop. Tip: Nearly all objects have a compare() method, and for primitives you can find a static compareTo() method in the wrapper class (for int it would be Integer.compareTo()). They work the same way: - will return a positive int if the first value is greater than the second value - will return a negative int if the second value is less than the first value - or 0 if compared values are equal

Andrei

Level 41

13 April 2021, 16:03

Thank you!

Andrei

Level 41

13 April 2021, 09:05

I have created a comparison logic, please let me know if it is ok:

@Override
           public int compare(Stock o1, Stock o2) {
              // o1.get()
               //i need to find a way to compare the name value in o1 with the name value in o2
               //maybe i should use a keyset?
               //maybe a treemap first considering they are sorted naturally

               TreeMap<String, Object> newTreeMapO1 = new TreeMap(o1);
               TreeMap<String, Object> newTreeMapO2 = new TreeMap(o2);

               String nameO1 = (String) newTreeMapO1.get("name");
               String nameo2 = (String) newTreeMapO2.get("name");

               int comparison = nameO1.compareToIgnoreCase(nameo2);
               return comparison ;

Thomas

Level 41 , Bayreuth, Germany

13 April 2021, 10:19

useful

o1.get() can't work cause you need to give it the key of the value you want to grab, eg. o1.get("name") that will return the value of type object. That you cast to String and can use the compareTo method. In the end you have smth. like: return ((String) o1.get("name")).compareTo((String) o2.get("name"));

Andrei

Level 41

13 April 2021, 11:44

Sorry, I should have mentioned to ignore line 50, it was incomplete.