The 100 most frequently occurring classes in Java

Most Java software development uses various libraries. Recently, we analyzed 10,000 open source Java projects and extracted the most commonly used Java classes. These classes come from Java's standard library and third-party libraries. Each class is counted only once in the same project, and the top 100 classes are shown in the list below.

The following list is sorted by the most commonly used class. The third value indicates the number of projects using this class among 10,000 projects. For the complete list, please see here.

1. java.util.ArrayList (6958)

2. java.io.IOException (6866)

3. ##java.util .List (6784)

##java.util.HashMap (5590)
java.util.Map (5413)
java.io.File (5097)
java.io.InputStream (4234)
java.util .Set (3915)

8. ##java.util.Arrays (3884)

9. java.util.Iterator (3856)

10. java.util.Collections (3643)

11. java.util.Date (3461)

12. java.util .HashSet (3278)

13. java.io.BufferedReader (3257)

14. java.util.Collection (3192)

15. java.net.URL (3168)

16. java.io.FileInputStream (3044)

17. java.io .InputStreamReader (3023)

18. ##org.junit.Test (3008)

19. ##java.io.FileOutputStream (2843)

20. java.io.FileNotFoundException (2669)

21. java.io.OutputStream (2563)

22. java.util .regex.Pattern (2469)

23. java.io.Serializable (2437)

24. java.util.LinkedList (2372)

25. java.text.SimpleDateFormat (2245)

##java.util.Properties (2190)
java .util.Random (2171)
java.lang.reflect.Method (2141)

28. ##java.io.ByteArrayOutputStream (2112)

29. java.util.regex.Matcher (2012)

30. android.os.Bundle (2007)

31. java.util.logging.Logger (1999)

32. java.io.UnsupportedEncodingException (1968)

33. ##org.junit.Before (1920)

34. java.util.Comparator (1896)

35. java.io.ByteArrayInputStream (1868)

36. java.io.PrintWriter (1862)

37. java.util.Calendar (1854)

38. android.app.Activity (1843)

39. java.net.MalformedURLException (1828)

40. android.content.Context (1780)

41. android.view.View (1731)

42. java.util.Locale (1719)

43. java.util.Enumeration (1709)

44. java.util.Map.Entry (1705)

45. ##java.io.FileWriter (1677)

46. java.io.FileReader (1651)

47. android.util.Log (1614)

48. android.content .Intent (1601)

49. java.lang.reflect.InvocationTargetException (1594)

50. java.util.logging.Level (1557)

51. java.lang.reflect.Field (1499)

52. java.io.StringWriter (1499)

53. android.widget.TextView (1442)

54. java.util.LinkedHashMap (1409)

55. java.io.Reader (1390 )

56. java.net.URI (1377)

57. java.io.Writer (1339)

58. java.text.ParseException (1318)

##junit.framework.TestCase (1318)

59. ##java.io.OutputStreamWriter (1295 )

60. java.io.StringReader (1279)

61. java.io.BufferedWriter (1265)

62. java.util.Vector (1254)

63. java.util.StringTokenizer (1251)

64. java.text.DateFormat (1246 )

65. java.util.concurrent.TimeUnit (1237)

66. java.io.BufferedInputStream (1235)

67. java.util.TreeMap (1227)

68. ##org.xml.sax.SAXException (1218)

69. javax.servlet .http.HttpServletRequest (1175)

70. java.io.PrintStream (1168)

71. java.util.TreeSet (1160)

72. android.widget.Toast (1157)

73. java.util.Hashtable (1154)

74. java .lang.reflect.Constructor (1139)

75. java.net.URLEncoder (1134)

76. java.security.NoSuchAlgorithmException (1134)

77. org.w3c.dom.Document (1130)

78. android.widget.Button (1129)

79. org.junit.After (1128)

80. javax.servlet.http.HttpServletResponse (1109)

81. java.awt.Color (1099)

82. java.net.URISyntaxException (1085)

83. ##javax.servlet.ServletException (1081)

84. javax.xml.parsers.DocumentBuilderFactory (1076)

85. java.lang.annotation.Retention (1075)

86. java.security.MessageDigest (1072)

87. java.util.concurrent.Executors (1062)

88. java.net.UnknownHostException (1057)

89. ##org.slf4j.Logger (1054)

90. java.sql.SQLException (1043)

91. org.slf4j.LoggerFactory (1042)

92. java.util.UUID (1040)

93. java.net.InetAddress (1026)

94. junit.framework.Assert (1011)

95. android.view.ViewGroup (1005)

96. java.util.concurrent.ConcurrentHashMap (1001)

97. java.awt.event.ActionEvent (995)

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