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Implementations of the singleton pattern ensure that only one instance of the singleton class ever exists and typically provide global access to that instance. Typically, this is accomplished by: Declaring all constructors of the class to be private, which prevents it from being instantiated by other objects
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.
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.
Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Patterns that imply mutable state may be unsuited for functional programming languages.
In Java [5]: 84 these are StringBuffer and StringBuilder (mutable versions of Java String) and in .NET this is StringBuilder (mutable version of .Net String). Python 3 has a mutable string (bytes) variant, named bytearray. [6] Additionally, all of the primitive wrapper classes in Java are immutable.
The implementation of the idiom relies on the initialization phase of execution within the Java Virtual Machine (JVM) as specified by the Java Language Specification (JLS). [3] When the class Something is loaded by the JVM, the class goes through initialization. Since the class does not have any static variables to initialize, the ...
Whereas the singleton allows only one instance of a class to be created, the multiton pattern allows for the controlled creation of multiple instances, which it manages through the use of a map. Rather than having a single instance per application (e.g. the java.lang.Runtime object in the Java programming language ) the multiton pattern instead ...
Final variables can be used to construct trees of immutable objects. Once constructed, these objects are guaranteed not to change anymore. To achieve this, an immutable class must only have final fields, and these final fields may only have immutable types themselves. Java's primitive types are immutable, as are strings and several other classes.