clerk.java

Beginning Java 2, SDK 1.4 Edition Exercise Code samples for this book

import java.util.List;
import java.util.Collections;
import java.util.LinkedList;

public class Clerk implements Runnable {
  Bank theBank;
  // The in-tray holding transactions:
  private List inTray = Collections.synchronizedList(new LinkedList());

  private int maxTransactions = 8;      // Maximum transactions in the in-tray.

  // Constructor
  public Clerk(Bank theBank) {
    this.theBank = theBank;          	// Who the clerk works for.
    //inTray     = null;                //Commented out: don't need this now.
  }

  // Receive a transaction:
  synchronized public void doTransaction(Transaction transaction) {
    while(inTray.size() >= maxTransactions) {
      try {
        wait();
      } catch(InterruptedException e) {
        System.out.println(e);
      }
    }
      inTray.add(transaction);
      notifyAll();
  }

  // The working clerk:
  synchronized public void run() {
    while(true) {
      while(inTray.size() == 0) {    // No transaction waiting?
        try {
          wait();                   // Then take a break until there is.
        } catch(InterruptedException e) {
          System.out.println(e);
        }
      }
      theBank.doTransaction((Transaction)inTray.remove(0));
      notifyAll();                  // Notify other threads locked on this clerk.
    }
  }

  // Busy check:
  synchronized public void isBusy() {
    while(inTray.size() != 0) {       // Is this object busy?
      try {
        wait();                       // Yes, so wait for notify call.
      } catch(InterruptedException e) {
        System.out.println(e);
      }
    }
    return;                           // It is free now.
  }
}