Copy on write arraylist api

Though we have an option to synchronize the collections like List or Set using synchronizedList or synchronizedSet methods respectively of the Collections class but there is a drawback to this synchronization ; very poor performance as the whole collection is locked and only a single thread can access it at a given time. Java also has a Vector class as a thread-safe alternative to List but that thread safety is achieved by synchronizing all the methods of the Vector class, which again results in poor performance. It is designed for concurrent access from multiple threads. This thread safety is achieved by making a fresh copy of the underlying array with every mutative operations add, set, and so on.

Copy on write arraylist api

It will take you to some of the most important topics for Java and JEE interviews, worth reading even if you are not preparing for Java interview. I am sure you have seen many of these questions personally on your interviews and many of you would have answered them correctly as well.

This is one of the tricky Java multi-threading questions you will see in senior Java developer Interview. Yes, you can make an array volatile in Java but only the reference which is pointing to an array, not the whole array.

What I mean, if one thread changes the reference variable to points to another array, that will provide a volatile guarantee, but if multiple threads are changing individual array elements they won't be having happens before guarantee provided by the volatile modifier.

This another good question I love to ask on volatile, mostly as a follow-up of the previous question. This question is also not easy to answer because volatile is not about atomicity, but there are cases where you can use a volatile variable to make the operation atomic.

One example I have seen is having a long field in your class.

CopyOnWriteArrayList (Java Platform SE 7 )

If you know that a long field is accessed by more than one thread e. One of the practical use of the volatile variable is to make reading double and long atomic. Both double and long are bit wide and they are read in two parts, first bit first time and next bit second time, which is non-atomic but volatile double and long read is atomic in Java.

copy on write arraylist api

Another use of the volatile variable is to provide a memory barrier, just like it is used in Disrupter framework. Basically, Java Memory model inserts a write barrier after you write to a volatile variable and a read barrier before you read it.

Which means, if you write to volatile field then it's guaranteed that any thread accessing that variable will see the value you wrote and anything you did before doing that right into the thread is guaranteed to have happened and any updated data values will also be visible to all threads, because the memory barrier flushed all other writes to the cache.

copy on write arraylist api

In some cases volatile also provide atomicity e. In terms of writing code, both will be of same complexity because synchronization code is independent of a number of threads.

Choice of synchronization though depends upon a number of threads because the number of thread present more contention, so you go for advanced synchronization technique e. Here is the standard idiom of using wait and notify method in Java: False sharing is very hard to detect because the thread may be accessing completely different global variables that happen to be relatively close together in memory.

Like many concurrency issues, the primary way to avoid false sharing is careful code review and aligning your data structure with the size of a cache line. Why should you use it? Busy spin is one of the technique to wait for events without releasing CPU.


It's often done to avoid losing data in CPU cached which is lost if the thread is paused and resumed in some other core. So, if you are working on low latency system where your order processing thread currently doesn't have any order, instead of sleeping or calling waityou can just loop and then again check the queue for new messages.Java Collection, ArrayList Exercises and solution: Write a Java program to copy one array list into another.

Java Collection, ArrayList Exercises: Copy one list into another Last update on September 04 (UTC/GMT +8 hours) Java Collection, ArrayList Exercises: Exercise-9 with Solution.

Write a Java program to copy one array list. * @param s the stream */ private void writeObject(benjaminpohle.comOutputStream s) throws benjaminpohle.comption{ // Write out element count, and any hidden stuff benjaminpohle.comtWriteObject(); Object[] elements = getArray(); int len =; // Write out array length benjaminpohle.comnt(len); // Write out all elements in the proper order.

The CopyOnWriteArrayList class uses a mechanism called copy-on-write which works like this: For every write operation (add, set, remove, etc) it makes a new copy of the elements in the list.

That means the read operations (get, iterator, listIterator, etc) work on a different copy. Working with Global Secondary Indexes: Java. You can use the AWS SDK for Java Document API to create a table with one or more global secondary indexes, describe the indexes on the table and perform queries using the indexes.

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The reason here is time complexity. The problem with arrays is that a remove operation can take O(n) time to complete. Really in Java this is an array copy of the remaining elements being moved to .

CopyOnWriteArrayList in Java is also an implementation of the List interface but it is a thread safe variant. This thread safety in CopyOnWriteArrayList is achieved by making a fresh copy of the underlying array with every mutative operations.

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