Exercises

Bruce Eckel's Thinking in Java Contents | Prev | Next

  1. Inherit a class from Thread and override the run( ) method. Inside run( ), print a message, then call sleep( ). Repeat this three times, then return from run( ). Put a start-up message in the constructor and override finalize( ) to print a shut-down message. Make a separate thread class that calls System.gc( ) and System.runFinalization( ) inside run( ), printing a message as it does so. Make several thread objects of both types and run them to see what happens.
  2. Modify Counter2.java so that the thread is an inner class and doesn’t need to explicitly store a handle to a Counter2.
  3. Modify Sharing2.java to add a synchronized block inside the run( ) method of TwoCounter instead of synchronizing the entire run( ) method.
  4. Create two Thread subclasses, one with a run( ) that starts up, captures the handle of the second Thread object and then calls wait( ). The other class’ run( ) should call notifyAll( ) for the first thread after some number of seconds have passed, so the first thread can print out a message.
  5. In Counter5.java inside Ticker2, remove the yield( ) and explain the results. Replace the yield( ) with a sleep( ) and explain the results.
  6. In ThreadGroup1.java, replace the call to sys.suspend( ) with a call to wait( ) for the thread group, causing it to wait for two seconds. For this to work correctly you must acquire the lock for sys inside a synchronized block.
  7. Change Daemons.java so that main( ) has a sleep( ) instead of a readLine( ). Experiment with different sleep times to see what happens.
  8. (Intermediate) In Chapter 7, locate the GreenhouseControls.java example, which consists of three files. In Event.java, the class Event is based on watching the time. Change Event so that it is a Thread, and change the rest of the design so that it works with this new Thread-based Event.



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