How can I replace a box of text with beamer?
You may try the overprint
environment (chap. 9.5, beamer user guide).
\documentclass{beamer}
\begin{document}
\begin{frame}{Quiz}
\begin{block}{Frage}
With generics the compiler has more information about the
types of the objects, so explicit casts don't have to be used
and the compiler can produce type safe code.
What implications have the generics for the runtime
performance of the program which uses them?
\end{block}
\begin{overprint}
\onslide<1>
\begin{itemize}
\item With the generics the compiler can optimize the code for
used types. This and the omission of the casts are the
reasons why the code compiled with the generics is
\textbf{quicker} than the one compiled without.
\item The usage of generics has \textbf{no implications} for
the runtime performance of the compiled programs.
\item The improved flexibility and type safety means that the
compiler has to generate concrete implementation from
the generic template for each used type. This means
that applications start \textbf{a bit slower}.
\end{itemize}
\onslide<2>
The Java Virtual Machine and the copiled byte code are Generics
agnostic. The comiled byte code does not differ from byte code
compiled from sources which don't use the generics.
So using the generics has \textbf{no impact} on the runtime
performance of compiled Java code.
\end{overprint}
\end{frame}
\end{document}