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Concrete classes have to explicitly declare they implement the immutable interface. This may not be possible if the concrete class "belongs to" third-party code, for instance, if it is contained within a library. The object is not really immutable and hence not suitable for use in data structures relying on immutability like hash maps.
In object-oriented (OO) and functional programming, an immutable object (unchangeable [1] object) is an object whose state cannot be modified after it is created. [2] This is in contrast to a mutable object (changeable object), which can be modified after it is created. [3]
Primitive wrapper classes are not the same thing as primitive types. Whereas variables, for example, can be declared in Java as data types double, short, int, etc., the primitive wrapper classes create instantiated objects and methods that inherit but hide the primitive data types, not like variables that are assigned the data type values.
Java's primitive types are immutable, as are strings and several other classes. If the above construction is violated by having an object in the tree that is not immutable, the expectation does not hold that anything reachable via the final variable is constant. For example, the following code defines a coordinate system whose origin should ...
The immutable keyword denotes data that cannot be modified through any reference. The const keyword denotes a non-mutable view of mutable data. Unlike C++ const, D const and immutable are "deep" or transitive, and anything reachable through a const or immutable object is const or immutable respectively. Example of const vs. immutable in D
For example, in the following Java code: class Foo { public int a ; } Foo a = new Foo (); Foo b = a ; a . prop = 3 ; a = new Foo (); a . prop = 1 ; Foo is a reference type, where a is initially assigned a reference of a new object, and b is assigned to the same object reference, i.e. bound to the same object as a , therefore, changes through a ...
One might desire to have a LinkedList of int, but this is not directly possible. Instead Java defines primitive wrapper classes corresponding to each primitive type: Integer and int, Character and char, Float and float, etc. One can then define a LinkedList using the boxed type Integer and insert int values into the list by boxing them as ...
Objects other than strings can be interned. For example, in Java, when primitive values are boxed into a wrapper object, certain values (any boolean, any byte, any char from 0 to 127, and any short or int between −128 and 127) are interned, and any two boxing conversions of one of these values are guaranteed to result in the same object. [6]