Threads - Beginning Java - page 787

You can test whether all tasks in a thread pool have been shut down by calling the isTerminated() meth-
od for the ExecutorService object. This method returns true if either shutdown() or shutdownNow() has
been called and all tasks have ended. The isShutdown() method returns true if the executor has been shut
down.
Let's try an executor in an example.

TRY IT OUT: Using an Executor
This example implements a version of the bank using an executor to execute the treads. The Account
and Transaction classes and the TransactionType enum are the same as for the previous example. I
call the class that defines the main() method UsingExecutors .
In this version of the bank, you create debit and credit transactions as tasks executing in separate threads
that submit transactions to the clerks. The tasks that create transactions are Callable<> tasks because
they need to return the total value of the debit or credit transactions that have been created for each ac-
count.

Generating Transactions
Here's a definition of the class identifying a source of transactions:

// Generates transactions for clerks
import java.util.Random;
import java.util.Vector;
import java.util.concurrent.Callable;

public class TransactionSource implements Callable<int[]> {

// Constructor
public TransactionSource(TransactionType type, int maxTrans,
Vector<Account> accounts,

Vector<Clerk> clerks) {
this.type = type;
this.maxTrans = maxTrans;
this.accounts = accounts;
this.clerks = clerks;
totals = new int[accounts.size()];

}

// The source of transactions
public int[] call() {
// Create transactions randomly distributed between the accounts
Random rand = new Random();
Transaction transaction = null; // Stores a

transaction
int amount = 0; // Stores

an amount of money
int select = 0; // Selects