Collection in java

The Java collections framework (JCF) is a set of classes and interfaces that implement commonly reusable collection data structures, it took shape with the release of JDK 1.2 and was expanded in JDK 1.4.
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java.util package contains all the classes and interfaces for Collection Framework. The Collection Framework provides a well-designed set Of interfaceS and classes for sorting and manipulating groups of data as a single unit.
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A List is an ordered Collection, List Interface extends the Collection Interface. List means that it cares about index of the object. It may contain duplicate elements.
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Set Interface also extends the Collection Interface. Set mean that it does not allow duplicate element i.e; it care about uniqueness.
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Map Interface also extends the Collection Interface. Map mean that it cares about the unique identifier i.e Map maps the unique key(ID) to a specific value. The Map implementation let do things like search value based on the key.
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The java Generics features were added to the java language from java 5/JDK 1.5. Before Generics ,we could put any thing in any ArrayList, LinkedList, Vector, HashSet, TreeSet, LinkedHashSet, HashMap, TreeMap, LinkedHashMap and HashTable.
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Generics allows us to add only one type of elements into the collections, that avoid change of error at runtime. We do not need to type cast the object while extracting from the collection.
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Java Generic's wildcards is a mechanism in Java Generics aimed at making it possible to cast a collection of a certain class, e.g P, to a collection of a subclass or superclass of P.
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Here are some collections example to better define the Collection concept.
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