Java 17 Recipes

 Solution 2
You can control when the main thread continues using a CountDownLatch object. In 
the following code, a CountDownLatch with an initial value of 2 is created; then, the two 
threads for loading the inventory and loading the order information are created and 
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started. As each of the two threads finishes executing, they call the CountDownLatch’s 
countDown() method, which decrements the latch’s value by one. The main thread waits 
until the CountDownLatch reaches 0, at which point it resumes execution.
public static void main(String[] args) {
Recipe10_7_2 recipe = new Recipe10_7_2();
recipe.start();
}
CountDownLatch latch = new CountDownLatch(2);
private void start() {
loadItems();
Thread inventoryThread = new Thread(() -> {
System.out.println("Loading Inventory from Database...");
loadInventory();
latch.countDown();
});
inventoryThread.start();
Thread ordersThread = new Thread(() -> {
System.out.println("Loading Orders from XML Web service...");
loadOrders();
latch.countDown();
});
ordersThread.start();
try {
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
processOrders();
}
The following is the output.
Loading Inventory from Database...
Loading Orders from XML Web service...
Order # 0 has been fulfilled
Order # 1 has been fulfilled
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Order # 2 has been fulfilled
Order # 3 has been fulfilled
Order # 4 has been fulfilled
Order # 5 has been fulfilled
Order # 6 has been fulfilled
Order # 7 has been fulfilled
Order # 8 has been fulfilled
Order # 9 has been fulfilled
Order # 10 has been fulfilled
Order # 11 has been fulfilled
Order # 12 has been fulfilled
Order # 13 has been fulfilled
...