Item 23: Don’t use raw types in new code

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1.  Raw types behave as if all of the generic type information were erased from the type declaration. For all practical purposes, the raw type List behaves the same way as the interface type List did before generics were added to the platform.

 

2.  It pays to discover errors as soon as possible after they are made, ideally at compile time. By using raw types, you don’t discover the error till runtime, long after it has happened, and in code that is far removed from the code containing the error. Once you see the ClassCastException, you have to search through the code base looking for the method invocation that put the wrong type into the collection.

 

3.  If you use raw types, you lose all the safety and expressiveness benefits of generics.

 

4.  It was deemed critical that all of legacy codes remain legal and interoperable with new code that does use generics. It had to be legal to pass instances of parameterized types to methods that were designed for use with ordinary types, and vice versa. This requirement, known as migration compatibility, drove the decision to support raw types.

 

5.  List is a subtype of the raw type List, but not of the parameterized type List