Possible.java is working well. First step to solve problem is successful.

--- Sudoku 9x9 ---
 5 3 . . 7 . . . .
 6 . . 1 9 5 . . .
 . 9 8 . . . . 6 .
 8 . . . 6 . . . 3
 4 . . 8 . 3 . . 1
 7 . . . 2 . . . 6
 . 6 . . . . 2 8 .
 . . . 4 1 9 . . 5
 . . . . 8 . . 7 9
known cells count: 30

cell#1{}
cell#2{}
cell#3{124}
cell#4{26}
cell#5{}
cell#6{2468}
cell#7{1489}
cell#8{1249}
cell#9{2489}
cell#10{}
cell#11{247}
cell#12{247}
cell#13{}
cell#14{}
cell#15{}
cell#16{3478}
cell#17{234}
cell#18{2478}
cell#19{12}
cell#20{}
cell#21{}
cell#22{23}
cell#23{34}
cell#24{24}
cell#25{13457}
cell#26{}
cell#27{247}
cell#28{}
cell#29{125}
cell#30{1259}
cell#31{579}
cell#32{}
cell#33{14}
cell#34{4579}
cell#35{2459}
cell#36{}
cell#37{}
cell#38{25}
cell#39{2569}
cell#40{}
cell#41{57}
cell#42{}
cell#43{579}
cell#44{259}
cell#45{}
cell#46{}
cell#47{15}
cell#48{1359}
cell#49{59}
cell#50{}
cell#51{14}
cell#52{4589}
cell#53{459}
cell#54{}
cell#55{139}
cell#56{}
cell#57{134579}
cell#58{357}
cell#59{357}
cell#60{}
cell#61{}
cell#62{}
cell#63{49}
cell#64{23}
cell#65{278}
cell#66{237}
cell#67{}
cell#68{}
cell#69{}
cell#70{36}
cell#71{3}
cell#72{}
cell#73{1239}
cell#74{1245}
cell#75{123459}
cell#76{2356}
cell#77{}
cell#78{26}
cell#79{13469}
cell#80{}
cell#81{49}

cell#71 is {3}