How To Work A Thread-Safe Concurrenthashset Inwards Coffee 8? Example
Until JDK 8, at that topographic point was no agency to practise a large, thread-safe, ConcurrentHashSet inwards Java. The java.util.concurrent parcel doesn't fifty-fifty conduct maintain a degree called ConcurrentHashSet, but from JDK 8 onwards, y'all tin hand notice exercise the newly added keySet(default value) as well as newKeySet() methods to practise a ConcurrentHashSet backed past times ConcurrentHashMap inwards Java. This is amend than former tactical solutions similar using a concurrent hash map amongst dummy value or using the gear upwards thought of the map, where y'all cannot add together novel elements. The Set returned past times keySet(defaultValue) as well as newKeySet() methods of JDK 8 is a proper set, where y'all tin hand notice besides add together novel elements along amongst performing other gear upwards operations e.g. contains(), remove() etc.
Though y'all require to endure a piffling fleck careful because these methods are entirely available inwards ConcurrentHashMap degree as well as non inwards ConcurrentMap interface, thence y'all require to exercise a ConcurrentHashMap reference variable to concur the reference, or y'all require to exercise type casting to cast a ConcurrentHashMap object stored inwards ConcurrentMap variable.
Btw, this is 1 of the many useful library enhancement introduce inwards JDK 8. If y'all desire to acquire to a greater extent than almost changes inwards Java 8, I propose y'all convey a appear at CopyOnArrayList for ArrayList, ConcurrentHahsMap for HashMap as well as CopyOnWriteArraySet for HashSet, but at that topographic point is cypher similar ConcurrentHashSet inwards Java.
Even though, CopyOnWriteArraySet is thread-safe it is non suitable for application where y'all require a large thread-safe set. It is entirely used for application where gear upwards sizes remain pocket-sized as well as read-only operations vastly outnumber write operations.
So, when y'all inquire Java programmers almost how to practise ConcurrentHashSet without writing their ain class, many volition country that they tin hand notice exercise ConcurrentHashMap amongst same values. This is inwards fact what Java besides does to practise HashSet. If y'all conduct maintain read my article how HashSet internally industrial plant inwards Java, y'all may think that HashSet internally uses HashMap amongst the same values.
But, the occupation amongst this approach is that y'all conduct maintain a map as well as non set. You cannot perform gear upwards operations on your ConcurrentHashMap amongst dummy values. You cannot exceed it unopen to when some method expects a Set, thence it's non rattling usable.
The other option, many Java programmer volition elevate that y'all tin hand notice acquire a Set thought from ConcurrentHashMap past times calling the keySet() method, which inwards fact furnish a Set, where y'all tin hand notice perform Set operations as well as exceed it unopen to to a method which expects a Set but this approach besides has its limitation.
For example, the Set is backed past times ConcurrentHashMap as well as whatsoever alter inwards Map volition reverberate inwards Set every bit well. Another limitation was that y'all cannot add together novel elements into this primal set, doing thence volition throw UnsupportedOperationException.
If y'all are non familiar almost this exception, I propose y'all join The Complete Java MasterClass - Updated for Java 11, 1 of the best resources to acquire Java past times yourself.
Anyway, both of these limitations are at 1 time affair of past times because JDK 8 has added newKeySet() method which returns a Set backed past times a ConcurrentHashMap from the given type where values are Boolean.TRUE.
Unlike Set thought returned from the keySet() method, y'all tin hand notice besides add together novel objects into this Set. The method is besides overloaded as well as accepts an initial capacity to forbid resizing of Set.
Btw, this is not the entirely way to practise a concurrent, large, thread-safe Set inwards Java.
You tin hand notice besides exercise the newly added, overloaded keySet(default value) method to practise a ConcurrentHashSet. This method returns a Set thought of the keys inwards the ConcurrentHashMap, using the given mutual default value for whatsoever additions (i.e., Collection.add() and Collection.addAll(Collection)).
This is of course of educational activity entirely exercise y'all tin hand notice exercise the same value for all elements inwards the Set, which is Ok inwards most situations because y'all don't actually attention almost values inwards Set. Remember, HashSet is besides a HashMap amongst the same values for all elements, See Set returned past times the keySet() method of ConcurrentHashMap, it throws UnsupportedOperationExcepiton as shown below:
Exception inwards thread "main" java.lang.UnsupportedOperationException
at java.util.concurrent.ConcurrentHashMap$KeySetView.add(ConcurrentHashMap.java:4594)
at Demo.main(Demo.java:23)
That's why I conduct maintain commented that code, but, Set returned past times newKeySet() as well as keySet(mapped value) methods allows y'all to add together novel elements into the Set, at that topographic point is no fault there.
By the way, this is non the entirely agency to practise a thread-safe Set inwards Java. Even earlier Java 8, at that topographic point is a degree called CopyOnWriteArraySet which allows y'all to practise a thread-safe gear upwards inwards Java.
It is similar to CopyOnWriteArrayList as well as entirely suitable for application where gear upwards size is pocket-sized as well as y'all entirely practise read the entirely functioning because it copies all elements from Set to a novel Set every fourth dimension y'all write into it. See Java SE 8 for the Really Impatient to acquire to a greater extent than almost concurrent collections inwards Java 8.
Here are some of the of import properties of CopyOnWriteArraySet:
1. It is best suited for applications inwards which gear upwards sizes to a greater extent than oft than non remain small, read-only operations vastly outnumber mutative operations, as well as y'all require to forbid interference amid threads during traversal.
That's all almost how to practise ConcurrentHashSet inwards Java 8. The JDK 8 API non entirely has major features similar lambda human face as well as current but besides these kinds of pocket-sized changes which brand your twenty-four hr catamenia to twenty-four hr catamenia coding easier. It's non super slow to practise a ConcurrentHashSet inwards Java using the newKeySet() method.
You don't require to exercise a map similar a gear upwards amongst a bogus value or alive amongst the limitation of gear upwards thought returned by keySet() which doesn't allow y'all to add together novel elements into the Set.
Further Learning
courses)20 Examples of Date as well as Time inwards Java 8 (tutorial) 5 Books to Learn Java 8 from Scratch (books) How to bring together String inwards Java 8 (example) How to exercise forEach() method inwards Java 8 (example) How to exercise filter() method inwards Java 8 (tutorial) 10 examples of Optionals in Java 8? (example) How to exercise Stream degree inwards Java 8 (tutorial) How to exercise peek() method inwards Java 8 (example) How to convert List to Map inwards Java 8 (solution) How to format/parse the engagement amongst LocalDateTime inwards Java 8? (tutorial) How to sort the map past times keys inwards Java 8? (example) 10 Java 8 Stream as well as Functional Programming Interview Questions (answers) How to exercise findFirst() method of Stream inwards Java 8 (example) Java 8 map + filter + collect + current instance (tutorial)
Thanks for reading this article thence far. If y'all similar this article as well as thence delight percentage amongst your friends as well as colleagues. If y'all conduct maintain whatsoever inquiry or feedback as well as thence delight drib a comment.
P. S. - If y'all don't heed learning from gratuitous resources as well as thence y'all tin hand notice besides depository fiscal establishment gibe out this listing of free Java 8 as well as Java nine courses to acquire better.
P. P. S. - If y'all similar to acquire from books then Java 8 inwards Action is the best mass to acquire both Java 8 features every bit good every bit other API enhancements made inwards JDK 8.
Though y'all require to endure a piffling fleck careful because these methods are entirely available inwards ConcurrentHashMap degree as well as non inwards ConcurrentMap interface, thence y'all require to exercise a ConcurrentHashMap reference variable to concur the reference, or y'all require to exercise type casting to cast a ConcurrentHashMap object stored inwards ConcurrentMap variable.
Btw, this is 1 of the many useful library enhancement introduce inwards JDK 8. If y'all desire to acquire to a greater extent than almost changes inwards Java 8, I propose y'all convey a appear at CopyOnArrayList for ArrayList, ConcurrentHahsMap for HashMap as well as CopyOnWriteArraySet for HashSet, but at that topographic point is cypher similar ConcurrentHashSet inwards Java.
Even though, CopyOnWriteArraySet is thread-safe it is non suitable for application where y'all require a large thread-safe set. It is entirely used for application where gear upwards sizes remain pocket-sized as well as read-only operations vastly outnumber write operations.
So, when y'all inquire Java programmers almost how to practise ConcurrentHashSet without writing their ain class, many volition country that they tin hand notice exercise ConcurrentHashMap amongst same values. This is inwards fact what Java besides does to practise HashSet. If y'all conduct maintain read my article how HashSet internally industrial plant inwards Java, y'all may think that HashSet internally uses HashMap amongst the same values.
But, the occupation amongst this approach is that y'all conduct maintain a map as well as non set. You cannot perform gear upwards operations on your ConcurrentHashMap amongst dummy values. You cannot exceed it unopen to when some method expects a Set, thence it's non rattling usable.
The other option, many Java programmer volition elevate that y'all tin hand notice acquire a Set thought from ConcurrentHashMap past times calling the keySet() method, which inwards fact furnish a Set, where y'all tin hand notice perform Set operations as well as exceed it unopen to to a method which expects a Set but this approach besides has its limitation.
For example, the Set is backed past times ConcurrentHashMap as well as whatsoever alter inwards Map volition reverberate inwards Set every bit well. Another limitation was that y'all cannot add together novel elements into this primal set, doing thence volition throw UnsupportedOperationException.
If y'all are non familiar almost this exception, I propose y'all join The Complete Java MasterClass - Updated for Java 11, 1 of the best resources to acquire Java past times yourself.
Anyway, both of these limitations are at 1 time affair of past times because JDK 8 has added newKeySet() method which returns a Set backed past times a ConcurrentHashMap from the given type where values are Boolean.TRUE.
Unlike Set thought returned from the keySet() method, y'all tin hand notice besides add together novel objects into this Set. The method is besides overloaded as well as accepts an initial capacity to forbid resizing of Set.
1. 1 ConcurrentHashSet using newKeySet() inwards Java 8
Here is a code instance to practise ConcurrentHashSet inwards Java 8:ConcurrentHashMap<String, Integer> certificationCosts = new ConcurrentHashMap<>(); Set<String>concurrentHashSet = certificationCosts.newKeySet(); concurrentHashSet.add("OCEJWCD"); //OK concurrentHashSet.contains("OCEJWCD"); //OK concurrentHashSet.remove("OCEJWCD"); //OK
Btw, this is not the entirely way to practise a concurrent, large, thread-safe Set inwards Java.
You tin hand notice besides exercise the newly added, overloaded keySet(default value) method to practise a ConcurrentHashSet. This method returns a Set thought of the keys inwards the ConcurrentHashMap, using the given mutual default value for whatsoever additions (i.e., Collection.add() and Collection.addAll(Collection)).
This is of course of educational activity entirely exercise y'all tin hand notice exercise the same value for all elements inwards the Set, which is Ok inwards most situations because y'all don't actually attention almost values inwards Set. Remember, HashSet is besides a HashMap amongst the same values for all elements, See Set returned past times the keySet() method of ConcurrentHashMap, it throws UnsupportedOperationExcepiton as shown below:
Exception inwards thread "main" java.lang.UnsupportedOperationException
at java.util.concurrent.ConcurrentHashMap$KeySetView.add(ConcurrentHashMap.java:4594)
at Demo.main(Demo.java:23)
That's why I conduct maintain commented that code, but, Set returned past times newKeySet() as well as keySet(mapped value) methods allows y'all to add together novel elements into the Set, at that topographic point is no fault there.
By the way, this is non the entirely agency to practise a thread-safe Set inwards Java. Even earlier Java 8, at that topographic point is a degree called CopyOnWriteArraySet which allows y'all to practise a thread-safe gear upwards inwards Java.
It is similar to CopyOnWriteArrayList as well as entirely suitable for application where gear upwards size is pocket-sized as well as y'all entirely practise read the entirely functioning because it copies all elements from Set to a novel Set every fourth dimension y'all write into it. See Java SE 8 for the Really Impatient to acquire to a greater extent than almost concurrent collections inwards Java 8.
Here are some of the of import properties of CopyOnWriteArraySet:
1. It is best suited for applications inwards which gear upwards sizes to a greater extent than oft than non remain small, read-only operations vastly outnumber mutative operations, as well as y'all require to forbid interference amid threads during traversal.
2. It is thread-safe.
3. Mutative operations (add, set, remove, etc.) are expensive since they commonly entail copying the entire underlying array.
4. Iterators practise non back upwards the mutative take operation.
5. Traversal via iterators is fast as well as cannot meet interference from other threads.
6. Iterators rely on unchanging snapshots of the array at the fourth dimension the iterators were constructed.
That's all almost how to practise ConcurrentHashSet inwards Java 8. The JDK 8 API non entirely has major features similar lambda human face as well as current but besides these kinds of pocket-sized changes which brand your twenty-four hr catamenia to twenty-four hr catamenia coding easier. It's non super slow to practise a ConcurrentHashSet inwards Java using the newKeySet() method.
You don't require to exercise a map similar a gear upwards amongst a bogus value or alive amongst the limitation of gear upwards thought returned by keySet() which doesn't allow y'all to add together novel elements into the Set.
Further Learning
courses)
Thanks for reading this article thence far. If y'all similar this article as well as thence delight percentage amongst your friends as well as colleagues. If y'all conduct maintain whatsoever inquiry or feedback as well as thence delight drib a comment.
P. S. - If y'all don't heed learning from gratuitous resources as well as thence y'all tin hand notice besides depository fiscal establishment gibe out this listing of free Java 8 as well as Java nine courses to acquire better.
P. P. S. - If y'all similar to acquire from books then Java 8 inwards Action is the best mass to acquire both Java 8 features every bit good every bit other API enhancements made inwards JDK 8.
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