Different fontsize for minted and mintinline

You can do even better, namely make \mintinline use the current font size.

The package minted allows for \setmintinline, that takes precedence over \setminted for \mintinline; the only trick is to define a macro that chooses the current font size.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{minted}

\makeatletter
\newcommand{\currentfontsize}{\fontsize{\f@size}{\f@baselineskip}\selectfont}
\makeatother

\setminted[java]{fontsize=\footnotesize}
\setmintedinline{fontsize=\currentfontsize}

\begin{document}

{\LARGE This is LARGE inline code: \mintinline{java}{Do.magic()}}

\bigskip

This is inline code: \mintinline{java}{Do.magic()}

And here a code block:
\begin{minted}{java}
    public class Magic(){
        public void do(){

        }
    }
\end{minted}

\end{document}