The CopyOnWriteArraySet.retainAll()
method in Java is used to retain only the elements in the CopyOnWriteArraySet
that are also contained in a specified collection.
Table of Contents
- Introduction
retainAll
Method Syntax- Examples
- Retaining Elements in a Collection
- Handling Non-Matching Elements
- Real-World Use Case
- Example: Retaining Specific Users in a Thread-Safe Set
- Conclusion
Introduction
The CopyOnWriteArraySet
is a thread-safe variant of Set
in Java. It is part of the java.util.concurrent
package and is designed for scenarios where read operations are more frequent than write operations. The retainAll
method allows you to retain only the elements in the set that are also contained in another collection. The CopyOnWriteArraySet
achieves thread safety by creating a new copy of the underlying array whenever it is modified.
retainAll() Method Syntax
The syntax for the retainAll
method is as follows:
public boolean retainAll(Collection<?> c)
- The method takes one parameter:
c
of typeCollection<?>
, which represents the collection containing elements to be retained in the set.
- The method returns
true
if the set changed as a result of the call, andfalse
otherwise.
Examples
Retaining Elements in a Collection
The retainAll
method can be used to retain only the elements in a CopyOnWriteArraySet
that are also contained in another collection.
Example
import java.util.ArrayList;
import java.util.concurrent.CopyOnWriteArraySet;
public class RetainAllExample {
public static void main(String[] args) {
// Creating a CopyOnWriteArraySet with String elements
CopyOnWriteArraySet<String> names = new CopyOnWriteArraySet<>();
// Adding elements to the CopyOnWriteArraySet
names.add("Ravi");
names.add("Priya");
names.add("Vijay");
// Creating another collection with String elements
ArrayList<String> retainNames = new ArrayList<>();
retainNames.add("Ravi");
retainNames.add("Priya");
// Retaining only the elements in names that are also in retainNames
boolean changed = names.retainAll(retainNames);
// Printing the CopyOnWriteArraySet and the result of the retainAll operation
System.out.println("CopyOnWriteArraySet: " + names);
System.out.println("Did the set change? " + changed);
}
}
Output:
CopyOnWriteArraySet: [Ravi, Priya]
Did the set change? true
Handling Non-Matching Elements
The retainAll
method does not change the CopyOnWriteArraySet
if none of the elements in the specified collection are contained in the set.
Example
import java.util.ArrayList;
import java.util.concurrent.CopyOnWriteArraySet;
public class NonMatchingElementsExample {
public static void main(String[] args) {
// Creating a CopyOnWriteArraySet with String elements
CopyOnWriteArraySet<String> names = new CopyOnWriteArraySet<>();
// Adding elements to the CopyOnWriteArraySet
names.add("Ravi");
names.add("Priya");
names.add("Vijay");
// Creating another collection with String elements
ArrayList<String> retainNames = new ArrayList<>();
retainNames.add("Anita");
retainNames.add("Suresh");
// Trying to retain elements in names that are in retainNames
boolean changed = names.retainAll(retainNames);
// Printing the CopyOnWriteArraySet and the result of the retainAll operation
System.out.println("CopyOnWriteArraySet: " + names);
System.out.println("Did the set change? " + changed);
}
}
Output:
CopyOnWriteArraySet: []
Did the set change? true
Real-World Use Case
Example: Retaining Specific Users in a Thread-Safe Set
A common real-world use case for CopyOnWriteArraySet
is managing a thread-safe set of users and retaining specific users based on certain criteria.
Example
import java.util.ArrayList;
import java.util.concurrent.CopyOnWriteArraySet;
public class UserSetManager {
public static void main(String[] args) {
// Creating a CopyOnWriteArraySet to manage user names
CopyOnWriteArraySet<String> userSet = new CopyOnWriteArraySet<>();
// Adding user names to the CopyOnWriteArraySet
userSet.add("Ravi");
userSet.add("Priya");
userSet.add("Vijay");
// Creating another collection with user names to retain
ArrayList<String> retainUserSet = new ArrayList<>();
retainUserSet.add("Ravi");
retainUserSet.add("Priya");
// Simulating concurrent operations
Thread retainThread = new Thread(() -> {
boolean changed = userSet.retainAll(retainUserSet);
System.out.println("Were users retained? " + changed);
});
Thread addThread = new Thread(() -> {
userSet.add("Anita");
System.out.println("Added user: Anita");
});
// Starting the threads
retainThread.start();
addThread.start();
// Waiting for the threads to finish
try {
retainThread.join();
addThread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
// Printing the final user set
System.out.println("Final user set: " + userSet);
}
}
Output:
Were users retained? true
Added user: Anita
Final user set: [Ravi, Priya, Anita]
In this example, CopyOnWriteArraySet
is used to manage a thread-safe set of user names, allowing concurrent operations while retaining specific users based on certain criteria.
Conclusion
The CopyOnWriteArraySet.retainAll()
method in Java provides a way to retain only the elements in a CopyOnWriteArraySet
that are also contained in a specified collection in a thread-safe manner. By understanding how to use this method, you can efficiently manage collections of elements in your Java applications, especially in concurrent environments. The method allows you to handle bulk retention operations, making it a versatile tool for data management in multi-threaded scenarios.