Threads - Analyzing exam questions - Sun Certified Java Programmer 310-065

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Title: Threads - Analyzing exam questions - Sun Certified Java Programmer 310-065 - Lesson 41

Duration: 17 minutes

Summary: In this video, we continue our discussion of threads. A running thread may enter a blocked/waiting state by calling wait(), sleep(), or join(). The reason it enters that state is that it cannot acquire the lock for a synchronized block of code. The wait method can take the number of milliseconds to wait (for example, 2000 milliseconds, or 2 seconds). The notifyAll() method must be called from a synchronized context. When a thread is waiting as a result of wait(), it releases its lock. In order to ensure the instances of a class can be safely used by multiple threads, we need to synchronize the public methods. If a piece of code does not acquire a lock on t before calling t.wait(), it throws IllegalMonitorStateException.

Methodology of the development of example: Good coding standard and simplified design to prepare for the Java programmer certification exam CX-310-065.

Technology Used: Java - Core Concepts.

Keywords: class, object, Thread, start(), run(), Runnable, sleep(), join(), wait(), notify(), notifyAll().

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Matthew Casperson
4/19/2012 8:5pm

Further explanation of Question 8

The explanation of question 8 is a bit vague.

Replacing the StringBuilder (which is not thread safe, see http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/StringBuilder.html) with StringBuffer (which is thread safe, see http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/StringBuffer.html) would mean that multiple threads could read and write to the contents object concurrently, but there is no guarantee that the sequence of append statements in the log() method would always be called in the order in which they are shown. One thread could append 2 lines, a second thread could append some lines, and the results would be garbled.

Synchronizing the log() method only could lead to the getContents() method being called while a thread is in the middle of appending a string to the contents object. With a StringBuilder, the results would be unpredictable. With a StringBuffer, you might see half a log message being printed out.

Synchronizing the getContents() method only could lead to the log() method being called while the thread is dumping the contents object. Again, with a StringBuilder the results of this concurrent access would be unpredictable.

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Mr.Bool Editor
4/24/2012 1:30pm

RE: We have forwarded your comment to the author.
soon, he will contact.

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Ayad
4/25/2012 7:38am

RE: Thank you for the feedback Matthew.

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Threads - Analyzing exam questions - Sun Certified Java Programmer 310-065 - Lesson 41 | Java courses

In this video, a running thread may enter a blocked/waiting state by calling wait(), sleep(), or join().