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The Java collections framework supports generics to specify the type of objects stored in a collection instance. In 1998, Gilad Bracha, Martin Odersky, David Stoutamire and Philip Wadler created Generic Java, an extension to the Java language to support generic types. [4] Generic Java was incorporated in Java with the addition of wildcards.
The Collection interface is a subinterface of java.lang.Iterable, so any Collection may be the target of a for-each statement. (The Iterable interface provides the iterator() method used by for-each statements.) All Collections have an java.util.Iterator that goes through all of the elements in the Collection. Collection is generic.
When primitive and value types are used as generic arguments, they get specialized implementations, allowing for efficient generic collections and methods. As in C++ and Java, nested generic types such as Dictionary<string, List<int>> are valid types, however are advised against for member signatures in code analysis design rules. [29]
Java has generics, which main purpose is to provide type-safe containers. C++ has compile-time templates, which provide more extensive support for generic programming and metaprogramming. Java has annotations, which allow adding arbitrary custom metadata to classes and metaprogramming via an annotation processing tool.
In the Java programming language, the wildcard? is a special kind of type argument [1] that controls the type safety of the use of generic (parameterized) types. [2] It can be used in variable declarations and instantiations as well as in method definitions, but not in the definition of a generic type.
Collections of data objects are typically stored in Java collection classes, such as implementations of the Set and List interfaces. Java generics, introduced in Java 5, are also supported. Hibernate can be configured to lazy load associated collections. [2]: 289–293 Lazy loading is the default as of Hibernate 3.
In particular, the original requirement was "… there should be a clean, demonstrable migration path for the Collections APIs that were introduced in the Java 2 platform". [46] This was designed so that any new generic collections should be passable to methods that expected one of the pre-existing collection classes. [80]
Memory access performance and the efficiency of 'boxed' value access are a major area to be addressed by these features. 'Value Type' features and 'Generic specialization' (when applied to lists or collections) reduce memory usage, but more importantly avoid pointer indirection which typically causes a cache miss. [8] [9]