are java collections thread safe?
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All collection classes (except Vector and Hashtable) in the java. util package are not thread-safe. The only two legacy collections are thread-safe: Vector and Hashtable. ... This is how you can synchronise a list in java.
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The differences between the Collection and Collections are given below. The Collection is an interface whereas Collections is a class. The Collection interface provides the standard functionality of data structure to List, Set, and Queue. However, Collections class is to sort and synchronize the collection elements.
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The principal built-in types are numerics, sequences, mappings, classes, instances and exceptions. Some collection classes are mutable. The methods that add, subtract, or rearrange their members in place, and don't return a specific item, never return the collection instance itself but None .
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Using Iterator can be used on any collection and since it doesn't have to be thread safe there is no additional locking overhead. In the example of the micro-benchmark given, the reason the Enumeration is faster than Iterator is because it is tested first. ;)
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HashMap is non synchronized. It is not-thread safe and can't be shared between many threads without proper synchronization code whereas Hashtable is synchronized. ... HashMap allows one null key and multiple null values whereas Hashtable doesn't allow any null key or value.
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HashSet is an unordered collection and doesn't maintain any order. ArrayList allows duplicate values in its collection. On other hand duplicate elements are not allowed in Hashset. ... On other hand Hashset allows only one null value in its collection,after which no null value is allowed to be added.
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The main reason that nulls aren't allowed in ConcurrentMaps (ConcurrentHashMaps, ConcurrentSkipListMaps) is that ambiguities that may be just barely tolerable in non-concurrent maps can't be accommodated. ... contains(key) , but in a concurrent one, the map might have changed between calls.
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Time complexity for ArrayDeque for accessing a element is O(1) and that for LinkList is is O(N) to access last element. ArrayDeque is not thread safe so manually synchronization is necessary so that you can access it through multiple threads and so they they are faster.
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Collection is a high-level interface describing Java objects that can contain collections of other objects. ... Collections are only iterable sequentially (and in no particular order) whereas a List allows access to an element at a certain position via the get(int index) method.
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The synchronized keyword prevents concurrent access to a block of code or object by multiple threads. All the methods of Hashtable are synchronized , so only one thread can execute any of them at a time.
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IEnumerable is best to query data from in-memory collections like List, Array etc. IEnumerable doesn't support add or remove items from the list. Using IEnumerable we can find out the no of elements in the collection after iterating the collection. IEnumerable supports deferred execution.
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A std::shared_ptr consists of a control block and its resource. Yes, the control block is thread-safe; but no, the access to the resource is not thread-safe. That means, modifying the reference counter is an atomic operation and you have the guarantee that the resource will be deleted exactly once.
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Class JsonParser. Implementation has no fields and therefore thread-safe, but sub-classes are not necessarily thread-safe. If a JSON map is encountered while using a destination class of type Map, then an ArrayMap is used by default for the parsed values.
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Gson instances are Thread-safe so you can reuse them freely across multiple threads.
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Entity Framework is not thread-safe. An MVC controller is instantiated per request. Thus if you use one DbContext per request, you're safe as long as you don't manually spawn threads in your controller actions (which you shouldn't do anyway).
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In for-each loop, we can't modify collection, it will throw a ConcurrentModificationException on the other hand with iterator we can modify collection. Modifying a collection simply means removing an element or changing content of an item stored in the collection.
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Each object gets its own copy of the class's instance variables - it's static variables that are shared between all instances of a class. The reason that instance variables are not necessarily thread-safe is that they might be simultaneously modified by multiple threads calling unsynchronized instance methods.