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[{“Name”:“Java SE 5”,“GroupName”:null},{“Name”:“Java SE 6”,“GroupName”:null},{“Name”:“Java SE 7”,“GroupName”:null},{“Name”:“Java SE 8”,“GroupName”:null},{“Name”:“Java SE 9 (Early Access)”,“GroupName”:null}]


Generics are a facility of generic programming that extend Java’s type system to allow a type or method to operate on objects of various types while providing compile-time type safety. In particular, the Java collections framework supports generics to specify the type of objects stored in a collection instance.



Generics are implemented in Java through Type erasure, which means that during runtime the Type information specified in the instantiation of a generic class is not available. For example, the statement List<String> names = new ArrayList<>(); produces a list object from which the element type String cannot be recovered at runtime. However, if the list is stored in a field of type List<String>, or passed to a method/constructor parameter of this same type, or returned from a method of that return type, then the full type information can be recovered at runtime through the Java Reflection API.

This also means that when casting to a generic type (e.g.: (List<String>) list), the cast is an unchecked cast. Because the parameter <String> is erased, the JVM cannot check if a cast from a List<?> to a List<String> is correct; the JVM only sees a cast for List to List at runtime.

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