Unsafe是位于sun.misc包下的一个类，主要提供一些用于执行低级别、不安全操作的方法，如直接访问系统内存资源、自主管理内存资源等，这些方法在提升Java运行效率、增强Java语言底层资源操作能力方面起到了很大的作用。但由于Unsafe类使Java语言拥有了类似C语言指针一样操作内存空间的能力，这无疑也增加了程序发生相关指针问题的风险。在程序中过度、不正确使用Unsafe类会使得程序出错的概率变大，使得Java这种安全的语言变得不再“安全”，因此对Unsafe的使用一定要慎重。
这个类尽管里面的方法都是 public 的，但是并没有办法使用它们，JDK API 文档也没有提供任何关于这个类的方法的解释。总而言之，对于 Unsafe 类的使用都是受限制的，只有授信的代码才能获得该类的实例，当然 JDK 库里面的类是可以随意使用的。
先来看下这张图，对UnSafe类总体功能：
https://avg.163.com/topic/detail/11253112
https://avg.163.com/topic/detail/11253110
https://avg.163.com/topic/detail/11253109
https://avg.163.com/topic/detail/11253108
https://avg.163.com/topic/detail/11253106
https://avg.163.com/topic/detail/11253107
https://avg.163.com/topic/detail/11253105
https://avg.163.com/topic/detail/11253103
https://avg.163.com/topic/detail/11253104
https://avg.163.com/topic/detail/11253102
https://avg.163.com/topic/detail/11253098
https://avg.163.com/topic/detail/11253100
https://avg.163.com/topic/detail/11253101
https://avg.163.com/topic/detail/11253099
https://avg.163.com/topic/detail/11253097
https://avg.163.com/topic/detail/11253096
https://avg.163.com/topic/detail/11253095
https://avg.163.com/topic/detail/11253094
https://avg.163.com/topic/detail/11253093
https://avg.163.com/topic/detail/11253092
https://avg.163.com/topic/detail/11253091
https://avg.163.com/topic/detail/11253090
https://avg.163.com/topic/detail/11253088
https://avg.163.com/topic/detail/11253089
https://avg.163.com/topic/detail/11253087
https://avg.163.com/topic/detail/11253086
https://avg.163.com/topic/detail/11253085
https://avg.163.com/topic/detail/11253084
https://avg.163.com/topic/detail/11253083
https://avg.163.com/topic/detail/11253082
https://avg.163.com/topic/detail/11253081
https://avg.163.com/topic/detail/11253080
https://avg.163.com/topic/detail/11253079
https://avg.163.com/topic/detail/11253076
https://avg.163.com/topic/detail/11253077
https://avg.163.com/topic/detail/11253078
https://avg.163.com/topic/detail/11253074
https://avg.163.com/topic/detail/11253075
https://avg.163.com/topic/detail/11253073
https://avg.163.com/topic/detail/11253072
https://avg.163.com/topic/detail/11253071
https://avg.163.com/topic/detail/11253070
https://avg.163.com/topic/detail/11253067
https://avg.163.com/topic/detail/11253069
https://avg.163.com/topic/detail/11253068
https://avg.163.com/topic/detail/11253066
https://avg.163.com/topic/detail/11253063
https://avg.163.com/topic/detail/11253065
https://avg.163.com/topic/detail/11253064
https://avg.163.com/topic/detail/11253062
https://avg.163.com/topic/detail/11253061
https://avg.163.com/topic/detail/11253060
https://avg.163.com/topic/detail/11253059
https://avg.163.com/topic/detail/11253058
https://avg.163.com/topic/detail/11253057
https://avg.163.com/topic/detail/11253055
https://avg.163.com/topic/detail/11253056
https://avg.163.com/topic/detail/11253054
https://avg.163.com/topic/detail/11253053
https://avg.163.com/topic/detail/11253052
https://avg.163.com/topic/detail/11253051
https://avg.163.com/topic/detail/11253050
https://avg.163.com/topic/detail/11253049
https://avg.163.com/topic/detail/11253048
https://avg.163.com/topic/detail/11253044
https://avg.163.com/topic/detail/11253047
https://avg.163.com/topic/detail/11253042
https://avg.163.com/topic/detail/11253043
https://avg.163.com/topic/detail/11253046
https://avg.163.com/topic/detail/11253045
https://avg.163.com/topic/detail/11253041
https://avg.163.com/topic/detail/11253040
https://avg.163.com/topic/detail/11253038
https://avg.163.com/topic/detail/11253037
https://avg.163.com/topic/detail/11253036
https://avg.163.com/topic/detail/11253035
https://avg.163.com/topic/detail/11253034
https://avg.163.com/topic/detail/11253033
https://avg.163.com/topic/detail/11253032
https://avg.163.com/topic/detail/11253031
https://avg.163.com/topic/detail/11253028
https://avg.163.com/topic/detail/11253030
https://avg.163.com/topic/detail/11253029
https://avg.163.com/topic/detail/11253027
https://avg.163.com/topic/detail/11253026
https://avg.163.com/topic/detail/11253025
https://avg.163.com/topic/detail/11253024
https://avg.163.com/topic/detail/11253023
https://avg.163.com/topic/detail/11253022
https://avg.163.com/topic/detail/11253021
https://avg.163.com/topic/detail/11253020
https://avg.163.com/topic/detail/11253019
https://avg.163.com/topic/detail/11253018
https://avg.163.com/topic/detail/11253012
https://avg.163.com/topic/detail/11253017
https://avg.163.com/topic/detail/11253016
https://avg.163.com/topic/detail/11253015
https://avg.163.com/topic/detail/11253014
https://avg.163.com/topic/detail/11253013
https://avg.163.com/topic/detail/11253011
https://avg.163.com/topic/detail/11253010
https://avg.163.com/topic/detail/11253008
https://avg.163.com/topic/detail/11253009
https://avg.163.com/topic/detail/11253007
https://avg.163.com/topic/detail/11253005
https://avg.163.com/topic/detail/11252999
https://avg.163.com/topic/detail/11253000
https://avg.163.com/topic/detail/11253001
https://avg.163.com/topic/detail/11252997
https://avg.163.com/topic/detail/11253006
https://avg.163.com/topic/detail/11253004
https://avg.163.com/topic/detail/11253003
https://avg.163.com/topic/detail/11253002
https://avg.163.com/topic/detail/11252998
https://avg.163.com/topic/detail/11252996
https://avg.163.com/topic/detail/11252994
https://avg.163.com/topic/detail/11252995
https://avg.163.com/topic/detail/11252993
https://avg.163.com/topic/detail/11252991
https://avg.163.com/topic/detail/11252990
https://avg.163.com/topic/detail/11252989
https://avg.163.com/topic/detail/11252988
https://avg.163.com/topic/detail/11252987
https://avg.163.com/topic/detail/11252986
https://avg.163.com/topic/detail/11252985
https://avg.163.com/topic/detail/11252984
https://avg.163.com/topic/detail/11252983
https://avg.163.com/topic/detail/11252982
https://avg.163.com/topic/detail/11252981
https://avg.163.com/topic/detail/11252980
https://avg.163.com/topic/detail/11252979
https://avg.163.com/topic/detail/11252977
https://avg.163.com/topic/detail/11252978
https://avg.163.com/topic/detail/11252975
https://avg.163.com/topic/detail/11252973
https://avg.163.com/topic/detail/11252976
https://avg.163.com/topic/detail/11252974
https://avg.163.com/topic/detail/11252972
https://avg.163.com/topic/detail/11252971
https://avg.163.com/topic/detail/11252970
https://avg.163.com/topic/detail/11252969
https://avg.163.com/topic/detail/11252968
https://avg.163.com/topic/detail/11252967
https://avg.163.com/topic/detail/11252965
https://avg.163.com/topic/detail/11252966
https://avg.163.com/topic/detail/11252964
https://avg.163.com/topic/detail/11252963
https://avg.163.com/topic/detail/11252962
https://avg.163.com/topic/detail/11252961
https://avg.163.com/topic/detail/11252960
https://avg.163.com/topic/detail/11252957
https://avg.163.com/topic/detail/11252959
https://avg.163.com/topic/detail/11252958
https://avg.163.com/topic/detail/11252956
https://avg.163.com/topic/detail/11252955
https://avg.163.com/topic/detail/11252954
https://avg.163.com/topic/detail/11252953
https://avg.163.com/topic/detail/11252952
https://avg.163.com/topic/detail/11252951
https://avg.163.com/topic/detail/11252950
https://avg.163.com/topic/detail/11252945
https://avg.163.com/topic/detail/11252947
https://avg.163.com/topic/detail/11252949
https://avg.163.com/topic/detail/11252948
https://avg.163.com/topic/detail/11252946
https://avg.163.com/topic/detail/11252944
https://avg.163.com/topic/detail/11252943
https://avg.163.com/topic/detail/11252941
https://avg.163.com/topic/detail/11252942
https://avg.163.com/topic/detail/11252940
https://avg.163.com/topic/detail/11252938
https://avg.163.com/topic/detail/11252939
https://avg.163.com/topic/detail/11252934
https://avg.163.com/topic/detail/11252936
https://avg.163.com/topic/detail/11252935
https://avg.163.com/topic/detail/11252933
https://avg.163.com/topic/detail/11252932
https://avg.163.com/topic/detail/11252930
https://avg.163.com/topic/detail/11252931
https://avg.163.com/topic/detail/11252929
https://avg.163.com/topic/detail/11252928
https://avg.163.com/topic/detail/11252927
https://avg.163.com/topic/detail/11252925
https://avg.163.com/topic/detail/11252924
https://avg.163.com/topic/detail/11252923
https://avg.163.com/topic/detail/11252922
https://avg.163.com/topic/detail/11252921
https://avg.163.com/topic/detail/11252920
https://avg.163.com/topic/detail/11252919
https://avg.163.com/topic/detail/11252918
https://avg.163.com/topic/detail/11252916
https://avg.163.com/topic/detail/11252917
https://avg.163.com/topic/detail/11252915
https://avg.163.com/topic/detail/11252914
https://avg.163.com/topic/detail/11252913
https://avg.163.com/topic/detail/11252912
https://avg.163.com/topic/detail/11252910
https://avg.163.com/topic/detail/11252909
https://avg.163.com/topic/detail/11252908
https://avg.163.com/topic/detail/11252907
https://avg.163.com/topic/detail/11252906
https://avg.163.com/topic/detail/11252903
https://avg.163.com/topic/detail/11252901
https://avg.163.com/topic/detail/11252904
https://avg.163.com/topic/detail/11252905
https://avg.163.com/topic/detail/11252900
https://avg.163.com/topic/detail/11252902
https://avg.163.com/topic/detail/11252899
https://avg.163.com/topic/detail/11252898
https://avg.163.com/topic/detail/11252897
https://avg.163.com/topic/detail/11252896
https://avg.163.com/topic/detail/11252895
https://avg.163.com/topic/detail/11252894
https://avg.163.com/topic/detail/11252893
https://avg.163.com/topic/detail/11252891
https://avg.163.com/topic/detail/11252890
https://avg.163.com/topic/detail/11252889
https://avg.163.com/topic/detail/11252888
https://avg.163.com/topic/detail/11252887
https://avg.163.com/topic/detail/11252886
https://avg.163.com/topic/detail/11252885
https://avg.163.com/topic/detail/11252884
https://avg.163.com/topic/detail/11252883
https://avg.163.com/topic/detail/11252878
https://avg.163.com/topic/detail/11252882
https://avg.163.com/topic/detail/11252881
https://avg.163.com/topic/detail/11252880
https://avg.163.com/topic/detail/11252879
https://avg.163.com/topic/detail/11252877
https://avg.163.com/topic/detail/11252876
https://avg.163.com/topic/detail/11252875
https://avg.163.com/topic/detail/11252874
https://avg.163.com/topic/detail/11252873
https://avg.163.com/topic/detail/11252872
https://avg.163.com/topic/detail/11252871
https://avg.163.com/topic/detail/11252870
https://avg.163.com/topic/detail/11252869
https://avg.163.com/topic/detail/11252868
https://avg.163.com/topic/detail/11252867
https://avg.163.com/topic/detail/11252849
https://avg.163.com/topic/detail/11252866
https://avg.163.com/topic/detail/11252865
https://avg.163.com/topic/detail/11252864
https://avg.163.com/topic/detail/11252863
https://avg.163.com/topic/detail/11252862
https://avg.163.com/topic/detail/11252861
https://avg.163.com/topic/detail/11252860
https://avg.163.com/topic/detail/11252859
https://avg.163.com/topic/detail/11252858
https://avg.163.com/topic/detail/11252857
https://avg.163.com/topic/detail/11252856
https://avg.163.com/topic/detail/11252855
https://avg.163.com/topic/detail/11252854
https://avg.163.com/topic/detail/11252853
https://avg.163.com/topic/detail/11252852
https://avg.163.com/topic/detail/11252851
https://avg.163.com/topic/detail/11252850
https://avg.163.com/topic/detail/11252848
https://avg.163.com/topic/detail/11252847
https://avg.163.com/topic/detail/11252846
https://avg.163.com/topic/detail/11252843
https://avg.163.com/topic/detail/11252845
https://avg.163.com/topic/detail/11252844
https://avg.163.com/topic/detail/11252839
https://avg.163.com/topic/detail/11252842
https://avg.163.com/topic/detail/11252841
https://avg.163.com/topic/detail/11252840
https://avg.163.com/topic/detail/11252838
https://avg.163.com/topic/detail/11252837
https://avg.163.com/topic/detail/11252836
https://avg.163.com/topic/detail/11252835
https://avg.163.com/topic/detail/11252834
https://avg.163.com/topic/detail/11252833
https://avg.163.com/topic/detail/11252832
https://avg.163.com/topic/detail/11252830
https://avg.163.com/topic/detail/11252831
https://avg.163.com/topic/detail/11252828
https://avg.163.com/topic/detail/11252829
https://avg.163.com/topic/detail/11252827
https://avg.163.com/topic/detail/11252826
https://avg.163.com/topic/detail/11252825
https://avg.163.com/topic/detail/11252824
https://avg.163.com/topic/detail/11252823
https://avg.163.com/topic/detail/11252822
https://avg.163.com/topic/detail/11252821
https://avg.163.com/topic/detail/11252820
https://avg.163.com/topic/detail/11252819
https://avg.163.com/topic/detail/11252818
https://avg.163.com/topic/detail/11252817
https://avg.163.com/topic/detail/11252816
https://avg.163.com/topic/detail/11252813
https://avg.163.com/topic/detail/11252815
https://avg.163.com/topic/detail/11252811
https://avg.163.com/topic/detail/11252809
https://avg.163.com/topic/detail/11252808
https://avg.163.com/topic/detail/11252812
https://avg.163.com/topic/detail/11252814
https://avg.163.com/topic/detail/11252810
https://avg.163.com/topic/detail/11252806
https://avg.163.com/topic/detail/11252807
https://avg.163.com/topic/detail/11252805
https://avg.163.com/topic/detail/11252804
https://avg.163.com/topic/detail/11252803
https://avg.163.com/topic/detail/11252801
https://avg.163.com/topic/detail/11252802
https://avg.163.com/topic/detail/11252800
https://avg.163.com/topic/detail/11252799
https://avg.163.com/topic/detail/11252798
https://avg.163.com/topic/detail/11252797
https://avg.163.com/topic/detail/11252793
https://avg.163.com/topic/detail/11252794
https://avg.163.com/topic/detail/11252795
https://avg.163.com/topic/detail/11252796
https://avg.163.com/topic/detail/11252792
https://avg.163.com/topic/detail/11252791
https://avg.163.com/topic/detail/11252790
https://avg.163.com/topic/detail/11252789
https://avg.163.com/topic/detail/11252788
https://avg.163.com/topic/detail/11252787
https://avg.163.com/topic/detail/11252785
https://avg.163.com/topic/detail/11252784
https://avg.163.com/topic/detail/11252783
https://avg.163.com/topic/detail/11252780
https://avg.163.com/topic/detail/11252781
https://avg.163.com/topic/detail/11252779
https://avg.163.com/topic/detail/11252778
https://avg.163.com/topic/detail/11252768
https://avg.163.com/topic/detail/11252772
https://avg.163.com/topic/detail/11252770
https://avg.163.com/topic/detail/11252776
https://avg.163.com/topic/detail/11252775
https://avg.163.com/topic/detail/11252773
https://avg.163.com/topic/detail/11252771
https://avg.163.com/topic/detail/11252769
https://avg.163.com/topic/detail/11252763
https://avg.163.com/topic/detail/11252765
https://avg.163.com/topic/detail/11252761
https://avg.163.com/topic/detail/11252760
https://avg.163.com/topic/detail/11252756
https://avg.163.com/topic/detail/11252757
https://avg.163.com/topic/detail/11252766
https://avg.163.com/topic/detail/11252764
https://avg.163.com/topic/detail/11252762
https://avg.163.com/topic/detail/11252759
https://avg.163.com/topic/detail/11252754
https://avg.163.com/topic/detail/11252753
