Top Most What is CyclicBarrier Example in Java 5 – Concurrency Tutorial

What is CyclicBarrier in Java

CyclicBarrier in Java is a synchronizer introduced in JDK 5 on java.util.Concurrent package along with other concurrent utility like Counting Semaphore, BlockingQueue, ConcurrentHashMap etc. CyclicBarrier is similar to CountDownLatch which we have seen in last article  What is CountDownLatch in Java and allows multiple threads to wait for each other (barrier) before proceeding. Difference between CountDownLatch and CyclicBarrier is a also very popular multi-threading interview question in Java. CyclicBarrier is a natural requirement for concurrent program because it can be used to perform final part of task once individual tasks  are completed. All threads which wait for each other to reach barrier are called parties, CyclicBarrier is initialized with number of parties to be wait and threads wait for each other by calling CyclicBarrier.await() method which is a blocking method in Java and  blocks until all Thread or parties call await(). In general calling await() is shout out that Thread is waiting on barrier. await() is a blocking call but can be timed out or Interrupted by other thread. In this Java concurrency tutorial we will see What is CyclicBarrier in Java  and  an example of CyclicBarrier on which three Threads will wait for each other before proceeding further.

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Top Most Difference between notify and notifyAll in Java - When and How to use

notify vs notifyAll in Java

What is difference between notify and notifyAll method is one of the tricky Java question, which is easy to answer but once Interviewer ask followup questions, you either got confused or not able to provide clear cut and to the point answers. Main difference between notify and notifyAll is that notify method will only notify one Thread and notifyAll method will notify all Threads  which are waiting on that monitor or lock. By the way this is something you have been reading in all over places and to be frank,  this statement despite being correct is not complete and its very difficult to understand difference between notify vs notifyAll by just reading this statement. Lot of questions comes in mind like

Which thread will be notified if I use notify()?

How do I know how many threads are waiting, so that I can use notifyAll() ?

How to call notify()?

What are these thread waiting for being notified etc.

Actually discussion of notify and notifyAll is incomplete without discussing wait method in Java and I had touched based on this on my earlier article why wait and notify must be called from synchronized context. In order to get answer of those questions and understand difference between notify and notifyAll we will use a simple Java Thread example using wait and notify code :

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Top Most How to implement Thread in Java ?Example of Runnable interface

How to implement Thread in Java
In my opinion Thread is the most wonderful feature of Java programming language and I remember when I started learning Java in one of programming class in India how important Thread was portrait and how much emphasis given on clear understanding of multi threading. It’s indeed still popular and one of most sought after skill in Java because writing concurrent and multi-threaded application in Java is challenging, despite Java providing excellent support at language level using synchronized and volatile keyword. Main problem with using multiple threads and writing multi-threaded code is issues related to concurrency e.g. deadlock, livelock,  race conditions etc, It takes lot of effort to implement multi-threading correctly in Java application.  In this core java tutorial I will share my experience on different way of implementing Thread in Java; Difference between Thread and Runnable in Java is also a very common core java interview question and asked mostly during junior level java interview.

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Top Most What is Timer and TimerTask in Java – Tutorial Example

Timer in Java is a utility class which is used to schedule tasks for both one time and repeated execution. Timer is similar to alarm facility many people use in mobile phone. Just like you can have one time alarm or repeated alarm, You can use java.util.Timer to schedule one time task or repeated task. In fact we can implement a Reminder utility using Timer in Java and that's what we are going to see in this example of Timer in Java. Two classes java.util.Timer and java.util.TimerTask is used to schedule jobs in Java and forms Timer API. TimerTask is actual task which is executed by Timer. Similar to Thread in Java, TimerTask also implements Runnable interface and overrides run method to specify task details. This Java tutorial will also highlight difference between Timer and TimerTask class and explains how Timer works in Java. By the way difference between Timer and Thread is also a popular Java questions on fresher level interviews.

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