Difference between revisions of "Generics"
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You '''CANNOT''' do this: | You '''CANNOT''' do this: | ||
<syntaxhighlight lang="java5"> | <syntaxhighlight lang="java5"> | ||
| − | List<Object> obj = new ArrayList<String>(); | + | List<Object> obj = new ArrayList<String>(); //NOT POSSIBLE |
</syntaxhighlight> | </syntaxhighlight> | ||
[[Category:OCPJP]] | [[Category:OCPJP]] | ||
Revision as of 02:56, 31 May 2011
- Generics is a way to enforce ONLY compile-time type safety.
- All the type information is not present at run-time. The compiler strips out type information from the bytecode using a process called type erasure.
- WHY Type erasure ? To ensure backward compatibility with legacy code.
- This compile-time safety is broken when generic and non-generic legacy code are mixed up.
- Watch out when autoboxing is involved with legacy code.
List l = new ArrayList();
l.add(123); //Auto-boxing happens.
int i = l.get(0); //Compile-time error. Autounboxing cant work because get() returns Object and not Integer.
Polymorphism and Generics
List<String> list = new ArrayList<String>();
Polymorphism only applies to the base type i.e list can be declared as arraylist You CANNOT do this:
List<Object> obj = new ArrayList<String>(); //NOT POSSIBLE
