Generics

generics allow one method to be used with several different data types
something similar can be done writing code using a supertype for all objects that will be passed to a method, but generics improve this by adding some checking at compile time to check type safety
both classes and methods can use generics to become more general
unlike C++, there is only one copy of a generic method produced in the finished bytecode (C++ produces one copy at compile time for each data type used to call the method in the code)
a procedure called erasure replaces all generic types with actual types in the compiled bytecode; the default type for this is Object
generic arguments are required to be generic, but algorithms often call for using primitive (built-in) data types; this isn't a big problem since all of the primitive data types in Java have corresponding wrapper classes (such as Integer for int)
Java's autoboxing and unboxing feature usually makes it easy to use wrapper classes such as Integer in place of their corresponding built-in type (in this case int)
Java generics can use wildcards (see the demonstration programs)
- ? extends ClassA: allows subclasses of ClassA
- ? super ClassA: allows superclasses of ClassA
you can use multiple bounds: T extends Comparable & Serializable
always put the most used bound first when using multiple bounds (for efficiency)
arrays of parameterized types are not allowed
you cannot use instantiation of a parameterized type such as: new T()