CopyOnWriteArraySet in Java

In Java, the CopyOnWriteArraySet is the part of the java.util.concurrent package and is used to handle thread-safe operations in multi-threaded environments. It is ideal when the set is frequently read but infrequently modified. The set ensures safe access for multiple threads, as it creates a new copy of the set each time a modification is made, making reads efficient and safe. However, this comes at the cost of slower performance for modifications.

• CopyOnWriteArraySet uses a CopyOnWriteArrayList internally.
• Multiple threads can perform updates simultaneously, but only one thread can iterate the set at a time without encountering ConcurrentModificationException.
• Iterators can only perform read operations. Any attempt to modify the set during iteration throws an  UnsupportedOperationException
• CopyOnWriteArraySet is Ideal for small sets where read operations are much more frequent than modifications, and where minimizing synchronization overhead is crucial.

CopyOnWriteArraySet is a class that implements the Set interface. The Set interface extends the Collection interface. The Collection interface extends the Iterable interface and the Object is the root of this hierarchy.

Example 1: This example demonstrates how CopyOnWriteArraySet allows safe concurrent reading and writing by multiple threads without throwing ConcurrentModificationException.

Set: [Geek1, Geek2, Geek3]
Added Geeks
Reading: Geek1
Reading: Geek2
Reading: Geek3

Hierarchy of CopyOnWriteArraySet

Declarartion of CopyOnWriteArraySet

In Java, the declaration of CopyOnWriteArraySet can be done as:

CopyOnWriteArraySet<Type> setName = new CopyOnWriteArraySet<>();

• Parameter: Specifies the type of elements the set will hold. It could be any class or interface, such as String or Integer.
• Return Type: Returns a thread-safe CopyOnWriteArraySet of the specified type.

Constructors

Example 2: This example demonstrates how CopyOnWriteArraySet allows thread-safe modification and iteration, where elements can be added by a child thread and safely iterated without causing concurrency issues or exception.

Set after child thread modification: [A, B, C, D]
[A, B, C, D]
[A, B, C, D]
[A, B, C, D]
[A, B, D]
Final Set: [A, B, D]

Example 3: This example demonstrates how to iterate over a CopyOnWriteArraySet, showing that it allows re-iteration without causing concurrency issues, even after elements are added.

Set contains:
GeeksforGeeks
Set contains after re-iteration:
GeeksforGeeks

Methods

• Method inherited from class java.util.AbstractSet:
  • hashCode(): Returns the hash code value for this set.
• Methods inherited from class java.util.AbstractCollection:
  • toString(): Returns a string representation of this collection
• Methods inherited from interface java.util.Collection:
  • parallelStream(): Returns a possibly parallel Stream with this collection as its source.
  • stream(): Returns a sequential Stream with this collection as its source.

HashSet vs CopyOnWriteArraySet