Generics

• 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