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Many languages have explicit pointers or references. Reference types differ from these in that the entities they refer to are always accessed via references; for example, whereas in C++ it's possible to have either a std:: string and a std:: string *, where the former is a mutable string and the latter is an explicit pointer to a mutable string (unless it's a null pointer), in Java it is only ...
Making a shallow copy of a const or immutable value removes the outer layer of immutability: Copying an immutable string (immutable(char[])) returns a string (immutable(char)[]). The immutable pointer and length are being copied and the copies are mutable. The referred data has not been copied and keeps its qualifier, in the example immutable.
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.
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]
String interning speeds up string comparisons, which are sometimes a performance bottleneck in applications (such as compilers and dynamic programming language runtimes) that rely heavily on associative arrays with string keys to look up the attributes and methods of an object. Without interning, comparing two distinct strings may involve ...
For function that manipulate strings, modern object-oriented languages, like C# and Java have immutable strings and return a copy (in newly allocated dynamic memory), while others, like C manipulate the original string unless the programmer copies data to a new string.
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.
In object-oriented programming, "immutable interface" is a pattern for designing an immutable object. [1] The immutable interface pattern involves defining a type which does not provide any methods which mutate state. Objects which are referenced by that type are not seen to have any mutable state, and appear immutable.