Change some public member to private.

Submit result:

Compilation:  PASSED
Style:        FAILED
Findbugs:     Potential bugs found.
API:          PASSED

Correctness:  15/25 tests passed
Memory:       8/8 tests passed
Timing:       0/17 tests passed

Raw score: 49.00% [Correctness: 65%, Memory: 10%, Timing: 25%, Style: 0%]