What is PhantomReference in Java?
Class PhantomReference Phantom references are most often used for scheduling pre-mortem cleanup actions in a more flexible way than is possible with the Java finalization mechanism. Unlike soft and weak references, phantom references are not automatically cleared by the garbage collector as they are enqueued.
How does phantom reference work?
Phantom reference objects, which are enqueued after the collector determines that their referents may otherwise be reclaimed. An object that is reachable via phantom references will remain so until all such references are cleared or themselves become unreachable.
How to use phantom reference in Java?
When we create an object in Java, an object is strong by default. To create a Phantom Reference Object, we must explicitly specify this to the JVM. Phantom Reference Objects are created as phantom reference object is eligible for garbage collection, but it is not collected instantly.
What is a weak reference Java?
A weakly referenced object is cleared by the Garbage Collector when it’s weakly reachable. Weak reachability means that an object has neither strong nor soft references pointing to it. The object can be reached only by traversing a weak reference.
What can I use instead of finalize?
synonyms for finalize
- agree.
- conclude.
- decide.
- settle.
- work out.
- wrap up.
- clinch.
- consummate.
What is WeakHashMap in Java?
WeakHashMap is an implementation of the Map interface that stores only weak references to its keys. Storing only weak references allows a key-value pair to be garbage-collected when its key is no longer referenced outside of the WeakHashMap. This class provides the easiest way to harness the power of weak references.
Is scanner a reference type Java?
Reference types are any instantiable class as well as arrays: String , Scanner , Random , Die , int[] , String[] , etc.
What is weak in Swift?
In Swift, strong references are the default, so to make a reference weak you can use the weak keyword. Unlike strong references, a weak reference does not affect an instance’s retain count. It does not hold onto the object. The only reason you need to use weak in Swift coding is to avoid strong reference cycles.
When Finalize method is called?
The finalize method is called when an object is about to get garbage collected. That can be at any time after it has become eligible for garbage collection. Note that it’s entirely possible that an object never gets garbage collected (and thus finalize is never called).
Why Finalize method is protected?
Why is the finalize() method’s access modifier is made as protected. Why cant it be public? It is not public because it shouldn’t be invoked by anyone other than the JVM. However, it must be protected so that it can be overridden by subclasses who need to define behavior for it.
Is WeakHashMap synchronized?
Like most collection classes, this class is not synchronized. A synchronized WeakHashMap may be constructed using the Collections. This class is intended primarily for use with key objects whose equals methods test for object identity using the == operator.
What is the difference between HashMap and ConcurrentHashMap?
HashMap is non-Synchronized in nature i.e. HashMap is not Thread-safe whereas ConcurrentHashMap is Thread-safe in nature. HashMap performance is relatively high because it is non-synchronized in nature and any number of threads can perform simultaneously.
How does a phantom reference work in Java?
An object that is reachable via phantom references will remain so until all such references are cleared or themselves become unreachable. Creates a new phantom reference that refers to the given object and is registered with the given queue. Returns this reference object’s referent.
What are the arguments to the phantomreference constructor?
The PhantomReference constructor accepts two arguments: q – the reference is registered with the given queue. The argument q represents the instance of the ReferenceQueue class. If the garbage collector determines that the referent of a phantom reference is phantom reachable, then the PhantomReference will be added to this ReferenceQueue.
Can a phantom reference be retrieved by the garbage collector?
In order to ensure that a reclaimable object remains so, the referent of a phantom reference may not be retrieved: The get method of a phantom reference always returns null . Unlike soft and weak references, phantom references are not automatically cleared by the garbage collector as they are enqueued.
What makes an object a phantom reachable in Java?
An object is phantom reachableif it is neither strongly nor softly nor weakly reachable and has been finalized and there is a path from the roots to it that contains at least one phantom reference. The PhantomReferenceconstructor accepts two arguments: referent- the object the new phantom reference will refer to
