Several hundred classes in the java.desktop module reply on default constructors as part of their public API.

This for the APIs in the javax.sound API

Default ctor on javax.sound.midi.VoiceStatus
Default ctor on javax.sound.midi.spi.MidiDeviceProvider
Default ctor on javax.sound.midi.spi.MidiFileReader
Default ctor on javax.sound.midi.spi.MidiFileWriter
Default ctor on javax.sound.midi.spi.SoundbankReader
Default ctor on javax.sound.sampled.spi.AudioFileReader
Default ctor on javax.sound.sampled.spi.AudioFileWriter
Default ctor on javax.sound.sampled.spi.FormatConversionProvider
Default ctor on javax.sound.sampled.spi.MixerProvider