在一個網站上，看了一下最常用的java類的統計，以下是前100.
1. java.util.List (2889)
2. java.util.ArrayList (2831)3. java.io.IOException (2813)
4. java.util.Map (2592)
5. java.util.HashMap (2541)
6. java.io.File (2195)
7. java.io.InputStream (2125)
8. java.util.Arrays (2068)
9. java.util.Collections (2028)
10. java.util.Set (2019)
11. java.util.Iterator (1954)
12. java.util.Collection (1734)
13. java.util.HashSet (1721)
14. java.util.Date (1679)
15. java.net.URL (1548)
16. java.io.FileInputStream (1495)
17. org.junit.Test (1463)
18. java.io.BufferedReader (1432)
19. java.io.OutputStream (1391)
20. java.io.InputStreamReader (1389)
21. java.io.FileOutputStream (1378)
22. java.util.regex.Pattern (1314)
23. java.io.FileNotFoundException (1294)
24. java.io.Serializable (1257)
25. java.lang.reflect.Method (1229)
26. java.io.ByteArrayOutputStream (1206)
27. java.util.LinkedList (1194)
28. java.util.Properties (1157)
29. java.text.SimpleDateFormat (1103)
30. java.io.ByteArrayInputStream (1079)
31. java.util.regex.Matcher (1064)
32. java.io.UnsupportedEncodingException (1047)
33. java.util.Locale (1009)
34. java.util.Comparator (1007)
35. org.junit.Before (1005)
36. java.util.Enumeration (949)
37. java.io.PrintWriter (931)
38. java.util.Random (928)
39. java.lang.reflect.InvocationTargetException (918)
40. java.net.MalformedURLException (916)
41. java.util.Map.Entry (899)
42. java.util.Calendar (859)
43. java.io.StringWriter (819)
44. java.lang.reflect.Field (790)
45. java.util.LinkedHashMap (788)
46. java.net.URI (781)
47. junit.framework.TestCase (720)
48. java.io.Reader (717)
49. java.io.Writer (706)
50. java.util.concurrent.TimeUnit (699)
51. java.io.FileReader (691)
52. java.io.FileWriter (682)
53. java.io.StringReader (680)
54. java.util.logging.Logger (677)
55. java.lang.reflect.Constructor (664)
56. java.text.ParseException (649)
57. java.net.URISyntaxException (644)
58. javax.servlet.http.HttpServletRequest (636)
59. java.lang.annotation.Retention (635)
60. java.util.TreeSet (632)
61. org.slf4j.Logger (627)
62. java.util.concurrent.ConcurrentHashMap (625)
63. java.io.OutputStreamWriter (622)
64. java.util.TreeMap (621)
65. java.util.StringTokenizer (619)
66. org.slf4j.LoggerFactory (618)
67. java.text.DateFormat (607)
68. android.os.Bundle (605)
69. org.junit.After (605)
70. javax.servlet.http.HttpServletResponse (603)
71. android.content.Context (603)
72. java.io.BufferedInputStream (600)
73. java.security.NoSuchAlgorithmException (592)
74. java.util.logging.Level (589)
75. java.lang.annotation.Target (588)
76. java.util.concurrent.Executors (588)
77. org.xml.sax.SAXException (586)
78. android.util.Log (583)
79. java.util.Vector (583)
80. android.content.Intent (578)
81. org.junit.runner.RunWith (577)
82. android.app.Activity (575)
83. javax.servlet.ServletException (568)
84. android.view.View (567)
85. java.lang.annotation.RetentionPolicy (559)
86. java.util.Hashtable (559)
87. java.security.MessageDigest (553)
88. junit.framework.Assert (548)
89. org.junit.Assert (548)
90. java.io.PrintStream (546)
91. java.net.InetAddress (537)
92. java.util.UUID (526)
93. android.widget.TextView (524)
94. java.net.URLEncoder (521)
95. org.w3c.dom.Document (521)
96. java.lang.annotation.ElementType (520)
97. java.net.UnknownHostException (518)
98. java.nio.charset.Charset (516)
99. java.io.BufferedWriter (513)
100. java.util.concurrent.ExecutorService (503)