単にJava叩きたいだけならメッセージ転送による自動委譲が一番手っ取り早いぞ
SmalltalkやPython、 Ruby、Goなんかだと簡単なのにJavaはかったるいからな

Example >> something: aThinDevice
| thinProtocol fatProtocol |
thinProtocol := aThinDevice thinProtocol.
thinProtocol selectorA.
thinProtocol selectorB.
thinProtocol selectorC.

fatProtocol := ( FatProtocolAdapter new ) withThinProtocol: thinProtocol.
fatPrococol selectorA. "thinProtocol selectorAへ委譲"
fatPrococol selectorB. "thinProtocol selectorBへ委譲"
fatPrococol selectorC. "thinProtocol selectorCへ委譲"
fatPrococol selectorD. "FatProtocolAdapterで新たに実装"

"FatProtocolAdapterが行ってる自動委譲"
FatProtocolAdapter >> doesNotUnderstand: aMessage
　aMessage sendTo: thinProtocol.

"あとは、初期化と差分のselectorDを追加するだけ"
FatProtocolAdapter >> withThinProtocol: aThinProtocol
　thinProtocol := aThinProtocol.

FatProtocolAdapter >> selectorD
　"固有処理"