Java 17 Recipes

7-6. Working with Dynamic Arrays
 Problem
You need a flexible data structure that can store a variable amount of data and allow for 
easy insertion and deletion of data.
 Solution
Consider using an ArrayList. The following example code is the StockScreener 
class, which allows you to screen a list of stocks or a single stock based on a specific 
screen parameter (P/E, Yield, and Beta) and screen value. The class uses an 
ArrayList for containing stock strings. An example screen might be “Tell me which 
of the stocks in this list has a P/E (price-to-earnings ratio) of 15 or less.” Don’t worry if 
you’re not familiar with these stock market terms. Whatever you do, don’t use this class 
to make your stock investment decisions!
public class StockScreener {
enum Screen { PE, YIELD, BETA };
public static boolean screen(String stock, Screen screen, double 
threshold) {
double screenVal = 0;
boolean pass = false;
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switch (screen) {
case PE:
screenVal = Math.random() * 25;
pass = screenVal <= threshold;
break;
case YIELD:
screenVal = Math.random() * 10;
pass = screenVal >= threshold;
break;
case BETA:
screenVal = Math.random() * 2;
pass = screenVal <= threshold;
break;
}
System.out.println(stock + ": " + screen.toString() + " =
" + screenVal);
return pass;
}
/**
* Parse through stock listing to determine if each stock passes the
* screen tests. If a particular element does not pass the screen,
then remove it.
*/
public static void screen(List stocks, Screen screen, double 
threshold) {
Iterator iter = stocks.iterator();
while (iter.hasNext()) {
String stock = iter.next();
if (!screen(stock, screen, threshold)) {
iter.remove();
}
}
}
public static void main(String[] args) {
List stocks = new ArrayList<>();
stocks.add("ORCL");
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stocks.add("AAPL");
stocks.add("GOOG");
stocks.add("IBM");
stocks.add("MCD");
System.out.println("Screening stocks: " + stocks);
if (stocks.contains("GOOG") &&
!screen("GOOG", Screen.BETA, 1.1)) {
stocks.remove("GOOG");
}
System.out.println("First screen: " + stocks);
StockScreener.screen(stocks, Screen.YIELD, 3.5);
System.out.println("Second screen: " + stocks);
StockScreener.screen(stocks, Screen.PE, 22);
System.out.println("Third screen: " + stocks);
System.out.println("Buy List: " + stocks);
}
}
The output from running this code varies because it randomly assigns a stock’s 
screen result value. Here is one sample of output from running the class.
Screening stocks: [ORCL, AAPL, GOOG, IBM, MCD]
GOOG: BETA = 1.9223516769748348
First screen: [ORCL, AAPL, IBM, MCD]
ORCL: YIELD = 6.140018494585904
AAPL: YIELD = 7.875759429097191
IBM: YIELD = 7.715436753622726
MCD: YIELD = 2.419792753509281
Second screen: [ORCL, AAPL, IBM]
ORCL: PE = 4.396013965331994
AAPL: PE = 14.200385457743778
IBM: PE = 7.6981860501796175
Third screen: [ORCL, AAPL, IBM]
Buy List: [ORCL, AAPL, IBM]
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