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java.util.Collection class and interface hierarchy Java's java.util.Map class and interface hierarchy. The Java collections framework is a set of classes and interfaces that implement commonly reusable collection data structures. [1] Although referred to as a framework, it works in a manner of a library. The collections framework provides both ...
In Java associative arrays are implemented as "maps", which are part of the Java collections framework. Since J2SE 5.0 and the introduction of generics into Java, collections can have a type specified; for example, an associative array that maps strings to strings might be specified as follows:
// DeadStoreExample.java import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class DeadStoreExample {public static void main (String [] args) {List < String > list = new ArrayList < String > (); // This is a Dead Store, as the ArrayList is never read.
Arrays are reified, meaning that an array object enforces its type information at run-time, whereas generics in Java are not reified. [6] More formally speaking, objects with generic type in Java are non-reifiable types. [6] A non-reifiable type is type whose representation at run-time has less information than its representation at compile ...
Collection classes are Java API-defined classes that can store objects in a manner similar to how data structures like arrays store primitive data types like int, double, long or char, etc., [2] but arrays store primitive data types while collections actually store objects. The primitive wrapper classes and their corresponding primitive types are:
The lazy initialization technique allows us to do this in just O(m) operations, rather than spending O(m+n) operations to first initialize all array cells. The technique is simply to allocate a table V storing the pairs ( k i , v i ) in some arbitrary order, and to write for each i in the cell T [ k i ] the position in V where key k i is stored ...
Java offers a set of overloaded binarySearch() static methods in the classes Arrays and Collections in the standard java.util package for performing binary searches on Java arrays and on Lists, respectively. [72] [73] Microsoft's .NET Framework 2.0 offers static generic versions of the binary search algorithm in its collection base classes.
If Entry were a value type, the array could store key-value pairs directly, eliminating the first indirection, increasing locality of reference and reducing memory use and heap fragmentation. Further, if Java supported generic primitive types, keys and values could be stored in the array directly, removing both levels of indirection.