Top Ten Concurrenthashmap Questions From Coffee Interviews
The ConcurrentHashMap aeroplane constituent of concurrent collections packet added on JDK 1.5 which contains utility classes like BlockingQueue, CopyOnWriteArrayList, CopyOnWriteArraySet etc. It is a replacement of synchronized hash-based map implementations e.g. Hashtable in addition to synchronized HashMap. It implements Map in addition to ConcurrentMap (a sub-interface of Map) interface which allows you lot to shop key-value pairs. The aeroplane is similar to HashMap or Hashtable precisely it's to a greater extent than scalable and the correct fit for concurrent Java application. Unlike Hashtable which achieves its thread-safety past times compromising the scalability, ConcurrentHashMap uses advanced techniques e.g. dividing the map into segments to stay thread-safe in addition to scalable at the same time.
Because of its performance in addition to scalability equally good equally thread-safety, it is the most pop selection of Map inwards concurrent Java applications.
In general, replacing synchronized collections alongside a concurrent collection tin dramatically improve the scalability of your Java application alongside a piddling risk, equally advised inwards of the classic Java mass of all time, the Java Concurrency inwards Practice book past times Brian Goetz.
If you lot receive got non read this mass in addition to so I highly recommend it to every unmarried Java programmer. Many of you lot may notice it hard when you lot read it the showtime fourth dimension precisely persist alongside it in addition to you lot volition reap the dividend inwards your career equally Java programmer.
If you lot notwithstanding notice concepts hard to sympathise you lot tin likewise convey assistance from Heinz Kabutz's awesome course Java Concurrency inwards Practice Bundle, which is based on this book. Heinz is ane of the Java champion in addition to first-class teacher who has gifted teaching skills. He explains hard concepts inwards such an slow linguistic communication in addition to examples which you lot tin correlate.
Anyway, let's start alongside this listing of Java interview questions based upon ConcurrentHashMap aeroplane in addition to concepts unopen to it.
These questions volition non exclusively assistance you lot to arrive at good on interviews precisely likewise encourage you lot to larn to a greater extent than almost the concurrent hash map, which volition eventually assistance you lot inwards your hateful solar daytime to hateful solar daytime programming job.
1. What is ConcurrentHashMap inwards Java? (answer)
The java.util.concurrent.ConcurrentHashMap is a concurrent collection aeroplane added on JDK 1.5 equally a replacement of synchronized hash-based map implementations e.g. Hashtable in addition to synchronized HashMap. They offering ameliorate performance in addition to scalability over their synchronized counterpart alongside piddling risk.
2. Does ConcurrentHashMap thread-safe inwards Java? (answer)
Yes, ConcurrentHashMap is thread-safe inwards Java, which agency ii thread tin modify the map without damaging its internal information construction e.g. array in addition to linked list. If you lot compare this to HashMap, which is non thread-safe, exposing HashMap to multiple threads may harm internal information structure in addition to may homecoming the map completely useless, where many links may acquire missing or pointing to incorrect elements.
3. How does ConcurrentHashMap attain thread-safety? (answer)
The java.util.ConcurrentHashMap achieves thread-safety past times dividing the map into segments in addition to locking exclusively the segment which requires instead of locking the whole map. So, yes, it achieves thread-safety using locking precisely it performs ameliorate because different HashMap, it never locks the whole map. This technique is likewise known equally lock stripping.
If you lot desire to larn to a greater extent than almost it, you lot tin likewise convey a aspect at answer)
Yes, ConcurrentHashMap allows concurrent read without locking equally reading functioning doesn't require locking or thread-safety.
5. Can ane thread read in addition to other writes on ConcurrentHashMap at the same time? (answer)
Yes, it's possible for a small-scale expose of the writer. For example, if a write functioning is modifying ane segment of ConcurrentHashmap in addition to read functioning is happening on other segments in addition to so a reader volition non block, precisely if reader thread is likewise trying to read from the same segment than it volition block until the author is done.
6. How does ConcurrentHashMap travel internally? (answer)
The java.util.ConcurrentHashMap industrial plant similar to HashMap when it comes to storing key/value pairs in addition to retrieving values. The exclusively departure inwards its implementation comes from concurrency perspective in addition to how it achievers thread-safety. It divides the map into several segments, past times default 16, likewise known equally synchronization level.
Because of this, concurrent get(), put(), contains() functioning is possible because it never locks the whole map precisely exclusively the relevant segment is locked. Which agency readers tin access the map concurrency alongside writers in addition to a express expose of writers tin modify the map concurrently. The trial is ameliorate throughput in addition to Scalability.
You tin farther come across The Complete Java MaseterClasss course of pedagogy on Udemy for details on the implementation of ConcurrentHashMap class. This course of pedagogy is latterly updated for Java 11, the latest Java version equally well.
Here is a diagram which explains how a segment looks similar inwards a ConcurrentHashMap of Java, basically it's cypher precisely a mini hash tabular array alongside a bucket in addition to a linked listing of hash entries inwards instance of collision:
Since the Iterator returned past times ConcurrentHashMap is weakly consistent, the recent concurrency modification may or may non live on visible to it. There is no guarantee offered on such operation.
I likewise propose you lot joining course Java Concurrency inwards Practice Bundle, to larn to a greater extent than almost how concurrency is handled past times ConcurrentHashMap inwards Java.
7. How arrive at you lot atomically update a value inwards ConcurrentHashMap? (answer)
If you lot desire to atomically update an existing value inwards ConcurrentHashMap, you lot tin purpose the replace() business office of concurrentHashMap.
It accepts both sometime value in addition to novel value in addition to exclusively updates the map if the existing value inwards the map matches alongside the sometime value provided, this agency the map is non concurrently modified during its call.
If the existing value is changed in addition to non matches alongside the sometime value in addition to so supervene upon neglect alongside returning false. You tin purpose telephone telephone the replace() method inwards land loop until you lot succeed, equally shown below:
You tin likewise see Java SE 8 for Really Impatient for some code examples of atomically updating an existing value inwards ConcurerntHashMap.
8. How arrive at you lot withdraw a mapping land iterating over ConcurrentHashMap? (answer)
You tin purpose an Iterator to withdraw a mapping from ConcurrentHashMap inwards Java equally shown below:
9. Does Iterator of ConcurrentHashMap is fail-safe or fail-fast? (answer)
Iterator of ConcurrentHashMap is a fail-safe iterator which agency it volition non throw a ConcurrentModificationException, thus, eliminating the demand to lock the map during iteration.
The Iterator returned past times ConcurrentHashMap are likewise weakly consistent which agency if the Map is modified during iteration, it may or may non reverberate the recent modification. Generally, it creates a re-create of collection earlier iterating.
10. What volition travel on if you lot add together a novel mapping inwards ConcurrentHashMap land ane thread is iterating over it? (answer)
This is ane of the tricky questions related to ConcurrentHashMap. Since iterator's of ConcurrentHashMap are weekly consistent in addition to fail-safe they volition non neglect alongside ConcurrentModificationException precisely it's likewise possible that they won't come across whatever modification ane time iteration started. Even though it's implementation dependent, JDK to a greater extent than often than non creates a separate re-create of ConcurrentHashMap for iteration, instead of iterating over master copy copy.
11. Can you lot travel past times an object of ConcurrentHahsMap when a Map is expected? (answer)
Yes because ConcurrentHashMap implements java.util.concurrent.ConcurrentMap interface, which extends java.util.Map interface, thus ConcurrentHashMap IS-A Map. Also, you lot tin shop an object of ConcurrentHashMap into a Map variable equally shown below:
Though, this means, you lot may non receive got access to methods declared inwards the java.util.concurrent.ConcurrentHashMap aeroplane e.g. forEachKey() or forEachValue() method added inwards Java 8.
That's all almost some of the frequently asked questions almost ConcurrentHashMap on Java interviews. These questions volition non exclusively assistance you lot to arrive at good on your undertaking interview precisely likewise encourage you lot to larn to a greater extent than almost ConcurrentHashMap.
Influenza A virus subtype H5N1 practiced in addition to enterprise noesis of ConcurrentHashMap is expected from both junior in addition to senior Java developer given its importance in addition to usability inwards every Java application.
At to the lowest degree you lot should live on comfortable alongside day-to-day operations alongside ConcurrentHashMap in addition to sympathise how the internal implementation works, peculiarly when compared to other thread-safe map implementations e.g. Hashtable in addition to Synchronized HashMap.
Further Learning
The Complete Java MasterClass
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Thanks for reading this article so far. If you lot similar these interview questions in addition to notice my explanations useful in addition to so delight part alongside your friends in addition to colleagues. If you lot receive got whatever enquiry or doubtfulness in addition to so delight driblet a comment.
Because of its performance in addition to scalability equally good equally thread-safety, it is the most pop selection of Map inwards concurrent Java applications.
In general, replacing synchronized collections alongside a concurrent collection tin dramatically improve the scalability of your Java application alongside a piddling risk, equally advised inwards of the classic Java mass of all time, the Java Concurrency inwards Practice book past times Brian Goetz.
If you lot receive got non read this mass in addition to so I highly recommend it to every unmarried Java programmer. Many of you lot may notice it hard when you lot read it the showtime fourth dimension precisely persist alongside it in addition to you lot volition reap the dividend inwards your career equally Java programmer.
If you lot notwithstanding notice concepts hard to sympathise you lot tin likewise convey assistance from Heinz Kabutz's awesome course Java Concurrency inwards Practice Bundle, which is based on this book. Heinz is ane of the Java champion in addition to first-class teacher who has gifted teaching skills. He explains hard concepts inwards such an slow linguistic communication in addition to examples which you lot tin correlate.
Anyway, let's start alongside this listing of Java interview questions based upon ConcurrentHashMap aeroplane in addition to concepts unopen to it.
Java ConcurrentHashMap Interview Questions alongside Answers
Here are some of the best in addition to ofttimes asked Java ConcurrentHashMap interview questions. These questions are collected from the existent interview, hence, don't live on surprised if you lot receive got already seen them during interviews.These questions volition non exclusively assistance you lot to arrive at good on interviews precisely likewise encourage you lot to larn to a greater extent than almost the concurrent hash map, which volition eventually assistance you lot inwards your hateful solar daytime to hateful solar daytime programming job.
1. What is ConcurrentHashMap inwards Java? (answer)
The java.util.concurrent.ConcurrentHashMap is a concurrent collection aeroplane added on JDK 1.5 equally a replacement of synchronized hash-based map implementations e.g. Hashtable in addition to synchronized HashMap. They offering ameliorate performance in addition to scalability over their synchronized counterpart alongside piddling risk.
2. Does ConcurrentHashMap thread-safe inwards Java? (answer)
Yes, ConcurrentHashMap is thread-safe inwards Java, which agency ii thread tin modify the map without damaging its internal information construction e.g. array in addition to linked list. If you lot compare this to HashMap, which is non thread-safe, exposing HashMap to multiple threads may harm internal information structure in addition to may homecoming the map completely useless, where many links may acquire missing or pointing to incorrect elements.
3. How does ConcurrentHashMap attain thread-safety? (answer)
The java.util.ConcurrentHashMap achieves thread-safety past times dividing the map into segments in addition to locking exclusively the segment which requires instead of locking the whole map. So, yes, it achieves thread-safety using locking precisely it performs ameliorate because different HashMap, it never locks the whole map. This technique is likewise known equally lock stripping.
If you lot desire to larn to a greater extent than almost it, you lot tin likewise convey a aspect at answer)
Yes, ConcurrentHashMap allows concurrent read without locking equally reading functioning doesn't require locking or thread-safety.
5. Can ane thread read in addition to other writes on ConcurrentHashMap at the same time? (answer)
Yes, it's possible for a small-scale expose of the writer. For example, if a write functioning is modifying ane segment of ConcurrentHashmap in addition to read functioning is happening on other segments in addition to so a reader volition non block, precisely if reader thread is likewise trying to read from the same segment than it volition block until the author is done.
6. How does ConcurrentHashMap travel internally? (answer)
The java.util.ConcurrentHashMap industrial plant similar to HashMap when it comes to storing key/value pairs in addition to retrieving values. The exclusively departure inwards its implementation comes from concurrency perspective in addition to how it achievers thread-safety. It divides the map into several segments, past times default 16, likewise known equally synchronization level.
Because of this, concurrent get(), put(), contains() functioning is possible because it never locks the whole map precisely exclusively the relevant segment is locked. Which agency readers tin access the map concurrency alongside writers in addition to a express expose of writers tin modify the map concurrently. The trial is ameliorate throughput in addition to Scalability.
You tin farther come across The Complete Java MaseterClasss course of pedagogy on Udemy for details on the implementation of ConcurrentHashMap class. This course of pedagogy is latterly updated for Java 11, the latest Java version equally well.
Here is a diagram which explains how a segment looks similar inwards a ConcurrentHashMap of Java, basically it's cypher precisely a mini hash tabular array alongside a bucket in addition to a linked listing of hash entries inwards instance of collision:
Since the Iterator returned past times ConcurrentHashMap is weakly consistent, the recent concurrency modification may or may non live on visible to it. There is no guarantee offered on such operation.
I likewise propose you lot joining course Java Concurrency inwards Practice Bundle, to larn to a greater extent than almost how concurrency is handled past times ConcurrentHashMap inwards Java.
7. How arrive at you lot atomically update a value inwards ConcurrentHashMap? (answer)
If you lot desire to atomically update an existing value inwards ConcurrentHashMap, you lot tin purpose the replace() business office of concurrentHashMap.
It accepts both sometime value in addition to novel value in addition to exclusively updates the map if the existing value inwards the map matches alongside the sometime value provided, this agency the map is non concurrently modified during its call.
If the existing value is changed in addition to non matches alongside the sometime value in addition to so supervene upon neglect alongside returning false. You tin purpose telephone telephone the replace() method inwards land loop until you lot succeed, equally shown below:
ConcurrentMap<String, Long> populationByCities = new ConcurrentHashMap<>(); do{ Long currentValue = populationByCities.get("New York"); Long newValue = currentValue == null ? 1 : currentValue + 1; }while(!populationByCities.replace("New York", currentValue, newValue));
You tin likewise see Java SE 8 for Really Impatient for some code examples of atomically updating an existing value inwards ConcurerntHashMap.
8. How arrive at you lot withdraw a mapping land iterating over ConcurrentHashMap? (answer)
You tin purpose an Iterator to withdraw a mapping from ConcurrentHashMap inwards Java equally shown below:
Map<String, Integer> bookAndPrice = novel ConcurrentHashMap<>(); bookAndPrice.put("Effective Java", 42); bookAndPrice.put("Head First Java", 29); bookAndPrice.put("Java Concurrency inwards Practice", 33); bookAndPrice.put("Head First Design Patterns", 41); System.out.println("before removing : " + bookAndPrice); Iterator<String> iterator = bookAndPrice.keySet().iterator(); while(iterator.hasNext()){ if(iterator.next().contains("Java")){ iterator.remove(); } } System.out.println("after removing : " + bookAndPrice); Output earlier removing : {Java Concurrency inwards Practice=33, Head First Design Patterns=41, Effective Java=42, Head First Java=29} after removing : {Head First Design Patterns=41}
9. Does Iterator of ConcurrentHashMap is fail-safe or fail-fast? (answer)
Iterator of ConcurrentHashMap is a fail-safe iterator which agency it volition non throw a ConcurrentModificationException, thus, eliminating the demand to lock the map during iteration.
The Iterator returned past times ConcurrentHashMap are likewise weakly consistent which agency if the Map is modified during iteration, it may or may non reverberate the recent modification. Generally, it creates a re-create of collection earlier iterating.
10. What volition travel on if you lot add together a novel mapping inwards ConcurrentHashMap land ane thread is iterating over it? (answer)
This is ane of the tricky questions related to ConcurrentHashMap. Since iterator's of ConcurrentHashMap are weekly consistent in addition to fail-safe they volition non neglect alongside ConcurrentModificationException precisely it's likewise possible that they won't come across whatever modification ane time iteration started. Even though it's implementation dependent, JDK to a greater extent than often than non creates a separate re-create of ConcurrentHashMap for iteration, instead of iterating over master copy copy.
11. Can you lot travel past times an object of ConcurrentHahsMap when a Map is expected? (answer)
Yes because ConcurrentHashMap implements java.util.concurrent.ConcurrentMap interface, which extends java.util.Map interface, thus ConcurrentHashMap IS-A Map. Also, you lot tin shop an object of ConcurrentHashMap into a Map variable equally shown below:
Map<String, Integer> bookAndPrice = new ConcurrentHashMap<>();
Though, this means, you lot may non receive got access to methods declared inwards the java.util.concurrent.ConcurrentHashMap aeroplane e.g. forEachKey() or forEachValue() method added inwards Java 8.
That's all almost some of the frequently asked questions almost ConcurrentHashMap on Java interviews. These questions volition non exclusively assistance you lot to arrive at good on your undertaking interview precisely likewise encourage you lot to larn to a greater extent than almost ConcurrentHashMap.
Influenza A virus subtype H5N1 practiced in addition to enterprise noesis of ConcurrentHashMap is expected from both junior in addition to senior Java developer given its importance in addition to usability inwards every Java application.
At to the lowest degree you lot should live on comfortable alongside day-to-day operations alongside ConcurrentHashMap in addition to sympathise how the internal implementation works, peculiarly when compared to other thread-safe map implementations e.g. Hashtable in addition to Synchronized HashMap.
Further Learning
The Complete Java MasterClass
list)
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