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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 ...
// 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.
Such classes can be referenced by using fully qualified names, or by importing only selected classes with different names. To do this, Java allows importing a single class (e.g., import java.util.List). C# allows importing classes under a new local name using the following syntax: using Console = System. Console.
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 hash function in Java, used by HashMap and HashSet, is provided by the Object.hashCode() method. Since every class in Java inherits from Object, every object has a hash function. A class can override the default implementation of hashCode() to provide a custom hash function more in accordance with the properties of the object.
import java.util.*; /*This form of importing classes makes all classes in package java.util available by name, could be used instead of the import declaration in the previous example. */ import java.*; /*This statement is legal, but does nothing, since there are no classes directly in package java.
Java generics generate only one compiled version of a generic class or function regardless of the number of parameterizing types used. Furthermore, the Java run-time environment does not need to know which parameterized type is used because the type information is validated at compile-time and is not included in the compiled code.
Since JDK 1.2, Java has included a standard set of collection classes, the Java collections framework Doug Lea , who also participated in the Java collections framework implementation, developed a concurrency package , comprising several concurrency primitives and a large battery of collection-related classes. [ 19 ]