What is a phantom reference in Java?

A phantom reference is a kind of reference in Java, where the memory can be reclaimed. The phantom reference is one of the strengths or levels of ‘non strong’ reference defined in the Java programming language; the others being weak and soft. An object is phantomly referenced after it has been finalized.

What is strong reference in Java?

Strong References: This is the default type/class of Reference Object. Any object which has an active strong reference are not eligible for garbage collection. The object is garbage collected only when the variable which was strongly referenced points to null.

What is Canonicalizing mappings in Java?

I have never understood the Java documentation for WeakReference, which says: A “canonicalized” mapping is where you keep one instance of the object in question in memory and all others look up that particular instance via pointers or somesuch mechanism. This is where weaks references can help.

What are strong soft weak and phantom references in Java?

Just remember that whilst Weak and Soft references are put in the queue after the object is finalized, Phantom references are put in the queue before. If for any reason you don’t poll the queue, the actual objects referenced by Phantom will not be finalized, and you can incur an OutOfMemory error.

What’s the difference between SoftReference and WeakReference?

WeakReference: is used to hold an object which will become eligible for the garbage collection as soon as it is not reachable by the program. SoftReference: lives longer, it will only be garbage collected before an OutOfMemoryError is thrown.

What is garbage collection in Java?

Java garbage collection is the process by which Java programs perform automatic memory management. Java programs compile to bytecode that can be run on a Java Virtual Machine, or JVM for short. The garbage collector finds these unused objects and deletes them to free up memory.

What is WeakReference in Kotlin?

WeakReference is known not to keep an object from being garbage collected, so if there’s no other reachable strong reference to it, it may be recycled at any moment once the method referencing it through local variable finishes. And this is exactly what happens in your case since the weak reference becomes null .

What are phantom references in Java?

A phantom reference is a reference type in association with a reference queue at the time of creation. Like soft and weak references, if a referent object has no other references other than phantom references, then the object is eligible for garbage collection. However, phantom references are different.

What are the different types of reference objects in Java?

Java provides two different types/classes of Reference Objects: strong and weak. Weak Reference Objects can be further divided into soft and phantom.

What is a strong reference in Java?

Strong References. A strong reference is a reference type that has the highest level of importance. An object that has an active strong reference to it, is not selected for garbage collection except when cylindrical references are used.

What is the default type of reference object?