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Phantom reference are the weakest level of reference in Java; in order from strongest to weakest, they are: strong, soft, weak, phantom. An object is phantomly referenced after it has been finalized. In Java 8 and earlier versions, the reference needs to be cleared before the memory for a finalized referent can be reclaimed.
A soft reference is a reference that is garbage-collected less aggressively. The soft reference is one of the strengths or levels of 'non strong' reference defined in the Java programming language, the others being weak and phantom. In order from strongest to weakest, they are: strong, soft, weak, phantom.
Object references in Java may be specified to be of an interface type; in each case, they must either be null, or be bound to an object that implements the interface. One benefit of using interfaces is that they simulate multiple inheritance. All classes in Java must have exactly one base class, the only exception being java.lang.Object (the ...
Integer are reference objects, on the surface no different from List, Object, and so forth. To convert from an int to an Integer , one had to "manually" instantiate the Integer object. As of J2SE 5.0, the compiler will accept the last line, and automatically transform it so that an Integer object is created to store the value 9 . [ 2 ]
Reference types include class types, interface types, and array types. When the constructor is called, an object is created on the heap and a reference is assigned to the variable. When a variable of an object gets out of scope, the reference is broken and when there are no references left, the object gets marked as garbage.
For object values, the reference cannot change. This allows the Java compiler to "capture" the value of the variable at run-time and store a copy as a field in the inner class. Once the outer method has terminated and its stack frame has been removed, the original variable is gone but the inner class's private copy persists in the class's own ...
For example, if one has a List reference in Java, one cannot invoke clone() on that reference because List specifies no public clone() method. Actual implementations of List like ArrayList and LinkedList all generally have clone() methods themselves, but it is inconvenient and bad abstraction to carry around the actual class type of an object.
With Java 5.0, additional wrapper classes were introduced in the java.util.concurrent.atomic package. These classes are mutable and cannot be used as a replacement for the regular wrapper classes. Instead, they provide atomic operations for addition, increment and assignment. The atomic wrapper classes and their corresponding types are: