For javax.sound.midi.Sequencer, the behaviour of several methods is not specified for the case that the Sequencer is not opened:
In the current implementation, start(), stop(), startRecording() and StopRecording() throw an IllegalStateException. This seems logical and should be specified the way it is implemented.
For setSequence(InputStream) and setSequence(Sequence), an IllegalStateException is thrown, too. However, it should be possible to set a Sequence even on a closed Sequencer. This should be specified explicitely, and the implementation changed.
For getSequence(), no exception is thrown. This is considered correct. However, it should be specified explicitly that this call is legal even on a closed Sequencer.