Question

I am trying to understand threads in Java. As an exercise, I created an Ice Cream class as follows.

public class ThreadIceCream {

private String flavor = "";
private String[] specialFlavors = { "Vanilla", "Chocolate", "Butter Pecan", "Strawberry", "Chocolate Chip", "Cherry", "Coffee" };
    // Constructor for ThreadIceCream class
public ThreadIceCream() {       
    int randInt = (int) (Math.random() * specialFlavors.length);
    flavor = specialFlavors[randInt];
    System.out.println("Enjoy your " + flavor + " IceCream!");
} }

The ThreadIceCream class is a simple class that creates an IceCream object with a random flavor every time the class is initialized. Here is the TestStub I am using.

public class TestStub {

public static void main(String[] args) {

    ThreadIceCream Th1 = new ThreadIceCream();
    ThreadIceCream Th2 = new ThreadIceCream();

} }

Now I want to create 10 Icecreams (i.e. Create 10 instances of the ThreadIceCream class simultaneously) and I want to use threads in Java to do this. I tried a few things but they were no were close.

Answer 1

Well it’s not really that hard:

Thread[] threads = new Thread[10];
for(int i = 0; i < 10; i++) {
    threads[i] = new Thread(new Runnable() {
                    public void run() {
                        ThreadIceCream tic = new ThreadIceCream();
                    }
                 });
    threads[i].start();
}

for(int i = 0; i < 10; i++) {
    threads[i].join();
}

Sure, this won’t do much because the work performed by each thread is so small that the overhead to start the threads is actually higher, but whatever.

You should also learn to use the ExecutorService for higher efficiency. Pure threads are heavyweight and are rarely a good solution for anything, especially in groups. Here’s an ExecutorService version of the above:

ExecutorService exec = Executors.newFixedThreadPool(10);
for(int i = 0; i < 10; i++) {
    exec.submit(new Runnable() {
                    public void run() {
                        ThreadIceCream tic = new ThreadIceCream();
                    }
                });        
}

exec.shutdown();
exec.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS);

Here we are creating a pool of 10 threads and submitting 10 tasks. The threads are recycled betweeen task executions, so only 10 threads are ever created, no matter how many tasks you submit. Since the tasks are so small several tasks may even be executed on the same thread, but that’s actually a good thing.