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Java Generics

Hi,

Can anyone please explain the difference of the three and each proper usage?

Thanks, been googling but I’m still confused on how to use each.

czetsuya

Answer 1

I’m assuming you’re talking about Generics. The ‘E’ and ‘T’ are placeholders and can be used interchangeably in class definitions. By convention ‘E’ is an Element and ‘T’ is a Type. The question mark is a placeholder for an unknown type. You often see things like this:

List<? extends MyObject> x;

This implies that ‘x’ is a list of objects that are subclasses of MyObject, but we don’t know what they are exactly.

See: http://docs.oracle.com/javase/tutorial/java/generics/genTypes.html