A Java Matlab/Julia Interface

In the Matlab code below I use Java to create a command-line interface to the external Julia program. Working in principle, I can experience (timing?) problems where the output is garbled, not complete, or delayed.

Are there better methods, how to assure the completion of the external program?

function obj = JuliaServer

% Use:
% jl = JuliaServer
% jl.start()
% jl.call('cos.(randn(3,3))')
% ...
% jl.stop()

import java.io.*
import java.net.*

%% properties

in = 0;
out = 0;
err = 0;

%% public methods

obj.start = @start;
obj.call = @call;
obj.stop = @stop;

%% methods

    function start
        rt = java.lang.Runtime.getRuntime();
        pr = rt.exec('julia -iq');
        in = BufferedReader(InputStreamReader(pr.getInputStream()));
        out = PrintWriter(pr.getOutputStream());
        err = BufferedReader(InputStreamReader(pr.getErrorStream()));
    end

    function [res, errmsg] = call(cmd)
        println(out, cmd);
        flush(out);
        while ~(ready(in) || ready(err)), end
        res = '';
        while (ready(in))
            res = append(res, sprintf('%s\n', strtrim(char(readLine(in)))));
        end
        errmsg = '';
        if ready(err)
            errmsg = sprintf('cmd: ''%s''\n', cmd);
            while (ready(err))
                errmsg = append(errmsg, sprintf('%s\n', strtrim(char(readLine(err)))));
            end
            error(errmsg)
        end
    end

    function stop
        println(out, 'exit()');
        out.flush();
    end

end