Java 17 Recipes

 How It Works
The ArrayList is one of the most often used classes in the Java collections 
framework. The ArrayList class implements the List interface, which, in turn, 
implements the Collection interface. The Collection interface defines the set 
of common operations for all collection types, and the List interface defines the set 
of operations that are specific to the list-oriented Collection types. The collections 
framework makes heavy use of Java generics.
The StockScreener main() method starts by declaring a List of stocks, and 
specifying with the generic type parameter, that the stocks list elements are of type 
String. Notice that the actual list type is an ArrayList created using the diamond. 
The stocks list holds a variable number of stocks, represented by their stock market 
symbol (a string).
List stocks = new ArrayList<>();
Now that you’ve specified that the stocks list can only hold strings, all the List 
methods, in turn, get parameterized to only allow strings. So, next, the code makes 
several calls to the ArrayList’s add(String) method to add the stocks to the list. 
After that, a screen is run on GOOG (Google) based on its beta (a measure of stock risk); 
if it does not pass the screen, the List remove(String) method is called to remove the 
stock from the stock list. Two more screens are then run on the entire stock list to get a 
list of stocks with a P/E of 22.0 or less and a yield of 3.5% or more. The screen() method 
used for these screens takes a parameter of type List. It has to iterate the list, 
run the screen for each stock, and remove those stocks that do not pass the screen. Note 
that to safely remove an element from a Collection while iterating over it, you must 
use iterate using the Collection’s Iterator, which can be obtained by calling 
its iterator() method. Here, we show the use of a while loop to iterate the stocks list 
(a for loop could similarly be used). As long as you’re not to the end of the list (iter.
hasNext()), you can get the next stock from the list (iter.next()), run the screen, and 
remove the element from the list (iter.remove()) if the screen didn’t pass.
Chapter 7 Data SourCeS anD ColleCtionS

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Note You may find that calling the list’s remove() method while iterating 
the list seems to work. the problem is that it’s not guaranteed to work 
and produce unexpected results. at some point, the code also throws 
ConcurrentModificationException, regardless of whether you have multiple 
threads accessing the same list. remember to always remove elements through 
the iterator when iterating over any Collection.
The ArrayList is a very useful data structure that should normally be used in 
place of the array type. It provides more flexibility than a simple array because elements 
can be added and removed dynamically with ease. While it is true that ArrayList uses 
an array internally, you benefit from optimized add() and remove() operations that are 
implemented for you. Also, ArrayList implements many other very useful methods.
Refer to Java documentation for more information (
https://docs.oracle.com/en/
java/javase/17/docs/api/java.base/java/util/ArrayList.html
).