An attempt to open a synthesizer leads to MidiUnavailableException if run with -Xfuture option.
Here is an example:
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package testapp.sound.midi;

import javax.sound.midi.MidiSystem;
import javax.sound.midi.Synthesizer;

public class OpenSynthesizer {

    public static void main(String[] args) {
        OpenSynthesizer inst = new OpenSynthesizer();
        
        try {
            inst.m1();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    public void m1() throws Exception {
        Synthesizer synth = MidiSystem.getSynthesizer();

        System.out.print("Opening synthesizer...");
        synth.open();
        System.out.println("...done");
        synth.close();
    }
}
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$ java -version
openjdk version "1.6.0-internal"
OpenJDK Runtime Environment (build 1.6.0-internal-dherron_19_dec_2007_13_45-b00)
Java HotSpot(TM) Client VM (build 11.0-b06, mixed mode)

$ java -Xfuture -cp . testapp.sound.midi.OpenSynthesizer
Opening synthesizer...javax.sound.midi.MidiUnavailableException: Audio Device Unavailable
        at com.sun.media.sound.MixerSynth.implOpen(MixerSynth.java:163)
        at com.sun.media.sound.AbstractMidiDevice.doOpen(AbstractMidiDevice.java:162)
        at com.sun.media.sound.AbstractMidiDevice.open(AbstractMidiDevice.java:126)
        at testapp.sound.midi.OpenSynthesizer.m1(OpenSynthesizer.java:22)
        at testapp.sound.midi.OpenSynthesizer.main(OpenSynthesizer.java:12)
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If no -Xfuture option is provided, the code works fine.