Wildcard (Java): Difference between revisions

Revision as of 12:21, 22 July 2014

Revision as of 12:26, 22 July 2014

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== Wildcard as parameter type ==

In the body of a generic unit, the (formal) type parameter is handled like its [[bounded quantification|upper bound]] (expressed with <code>'''extends'''</code>; <code>Object</code> if not constrained). If the return type of a method is the type parameter, the result (e.g. of type <code>?</code>) can be referenced by a variable of the type of the upper bound (or <code>Object</code>). In the other direction, the wildcard fits to no other type, not even to <code>Object</code>: If <code>?</code> has been applied foras the formal type parameter of a method, no actual parameters can be passed to it. It can be called only by casting of the wildcard reference:

<source lang="java5">