// "Replace with lambda" "true-preview" class Test { static class SetSubThreadReadPacket { private String getPostId() { return null; } } public void processPacket(String p) { IPacketProcessor iPacketProcessor = new IPacketProcessordReadPacket>() { public void process(SetSubThreadReadPacket p) { String root = p.getPostId(); } }; } private interface IPacketProcessor { void process(SetSubThreadReadPacket p); } }