最常用的1000个Java类（附代码示例）
分析Github3000个开源项目，粗略统计如下。括号内的数字是使用频率0－3000.下面的列表显示不全，完整的请看完整列表。
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)
101.javax.xml.parsers.DocumentBuilderFactory(487)
102.java.nio.ByteBuffer(481)
103.java.io.ObjectInputStream(481)
104.java.util.concurrent.atomic.AtomicInteger(467)
105.java.io.ObjectOutputStream(467)
106.android.widget.Toast(466)
107.java.util.NoSuchElementException(466)
108.org.w3c.dom.Element(463)
109.java.util.LinkedHashSet(461)
110.java.io.BufferedOutputStream(461)
111.java.math.BigInteger(459)
112.android.os.Handler(451)
113.org.junit.BeforeClass(450)
114.android.content.SharedPreferences(449)
115.android.content.DialogInterface(449)
116.android.view.ViewGroup(444)
117.java.math.BigDecimal(443)
118.java.lang.reflect.Modifier(441)
119.android.net.Uri(437)
120.javax.xml.parsers.ParserConfigurationException(437)
121.java.net.Socket(436)
122.android.app.AlertDialog(436)
123.org.w3c.dom.NodeList(428)
124.java.util.Stack(428)
125.android.widget.Button(428)
126.javax.xml.parsers.DocumentBuilder(427)
127.java.net.URLConnection(426)
128.android.view.LayoutInflater(423)
129.org.w3c.dom.Node(422)
130.java.util.TimeZone(422)
131.java.sql.SQLException(421)
132.android.widget.ListView(406)
133.org.xml.sax.InputSource(405)
134.org.apache.log4j.Logger(398)
135.android.view.MenuItem(394)
136.android.widget.ImageView(394)
137.org.apache.http.HttpResponse(389)
138.org.apache.http.impl.client.DefaultHttpClient(388)
139.java.net.HttpURLConnection(387)
140.org.junit.Ignore(386)
141.java.net.InetSocketAddress(385)
142.android.util.AttributeSet(383)
143.java.lang.reflect.Array(383)
144.android.view.View.OnClickListener(380)
145.android.widget.AdapterView(376)
146.android.widget.EditText(374)
147.android.database.Cursor(374)
148.android.view.Menu(374)
149.android.graphics.Bitmap(372)
150.java.io.DataInputStream(366)
151.java.io.DataOutputStream(362)
152.java.util.zip.ZipEntry(357)
153.android.widget.LinearLayout(354)
154.javax.servlet.http.HttpServlet(352)
155.java.text.DecimalFormat(350)
156.java.util.concurrent.Callable(350)
157.org.apache.commons.lang.StringUtils(349)
158.java.io.FilenameFilter(346)
159.java.util.GregorianCalendar(346)
160.java.text.MessageFormat(344)
161.java.awt.Color(340)
162.android.view.KeyEvent(337)
163.java.lang.annotation.Annotation(336)
164.java.net.URLDecoder(336)
165.java.util.concurrent.Future(335)
166.android.graphics.drawable.Drawable(332)
167.android.content.res.Resources(331)
168.java.util.concurrent.atomic.AtomicBoolean(329)
169.android.preference.PreferenceManager(328)
170.android.widget.ArrayAdapter(327)
171.android.view.MotionEvent(326)
172.org.apache.commons.logging.Log(325)
173.java.util.ResourceBundle(324)
174.android.app.Dialog(324)
175.org.apache.commons.logging.LogFactory(321)
176.java.util.concurrent.ExecutionException(320)
177.java.lang.ref.WeakReference(320)
178.android.graphics.Canvas(319)
179.java.sql.ResultSet(319)
180.android.os.AsyncTask(317)
181.org.apache.http.client.methods.HttpGet(317)
182.java.sql.Connection(317)
183.java.util.Queue(315)
184.java.io.Closeable(313)
185.android.content.ContentValues(311)
186.java.util.ListIterator(311)
187.android.content.BroadcastReceiver(307)
188.org.apache.commons.io.IOUtils(305)
189.android.content.pm.PackageManager(301)
190.android.preference.PreferenceActivity(299)
191.org.junit.AfterClass(299)
192.android.os.Message(296)
193.android.graphics.Color(295)
194.java.net.ServerSocket(295)
195.org.json.JSONObject(294)
196.org.apache.http.client.HttpClient(292)
197.java.util.TimerTask(291)
198.java.util.concurrent.CountDownLatch(289)
199.android.app.ProgressDialog(287)
200.java.awt.event.ActionEvent(287)
201.javax.servlet.ServletContext(285)
202.android.view.Window(285)
203.java.util.Timer(285)
204.android.graphics.BitmapFactory(281)
205.android.database.sqlite.SQLiteDatabase(278)
206.java.awt.image.BufferedImage(276)
207.android.os.IBinder(276)
208.java.lang.reflect.Type(275)
209.java.util.SortedSet(274)
210.android.content.ComponentName(273)
211.java.text.NumberFormat(272)
212.android.app.PendingIntent(271)
213.java.awt.event.ActionListener(269)
214.org.osgi.framework.BundleContext(269)
215.java.util.concurrent.LinkedBlockingQueue(267)
216.java.util.concurrent.atomic.AtomicLong(267)
217.android.text.TextUtils(267)
218.org.json.JSONException(265)
219.org.apache.commons.io.FileUtils(264)
220.javax.servlet.ServletRequest(263)
221.org.apache.http.HttpEntity(263)
222.android.widget.BaseAdapter(263)
223.android.os.Build(263)
224.java.util.zip.GZIPInputStream(260)
225.java.awt.Dimension(259)
226.org.xml.sax.Attributes(258)
227.android.widget.AdapterView.OnItemClickListener(257)
228.android.os.Environment(257)
229.java.util.concurrent.CopyOnWriteArrayList(256)
230.java.io.FileFilter(255)
231.javax.xml.transform.stream.StreamResult(255)
232.android.app.Service(253)
233.android.app.ListActivity(252)
234.android.view.Gravity(251)
235.javax.swing.JPanel(251)
236.javax.swing.JFrame(250)
237.javax.servlet.ServletResponse(249)
238.android.database.sqlite.SQLiteOpenHelper(249)
239.java.security.SecureRandom(248)
240.android.graphics.Rect(247)
241.junit.framework.Test(246)
242.java.net.URLClassLoader(245)
243.junit.framework.TestSuite(245)
244.android.graphics.Paint(245)
245.org.apache.http.client.methods.HttpPost(244)
246.java.util.concurrent.BlockingQueue(243)
247.java.util.concurrent.ConcurrentMap(242)
248.javax.imageio.ImageIO(241)
249.android.content.pm.PackageManager.NameNotFoundException(241)
250.java.util.EnumSet(238)
251.java.nio.channels.FileChannel(236)
252.javax.xml.transform.TransformerFactory(236)
253.java.util.concurrent.locks.ReentrantLock(236)
254.android.view.WindowManager(234)
255.android.content.ContentResolver(234)
256.java.sql.PreparedStatement(234)
257.org.json.JSONArray(234)
258.javax.inject.Inject(233)
259.android.content.IntentFilter(233)
260.java.util.WeakHashMap(233)
261.javax.swing.JLabel(232)
262.java.net.SocketException(232)
263.javax.xml.transform.Transformer(231)
264.android.view.ContextMenu(229)
265.javax.servlet.http.HttpSession(228)
266.java.lang.reflect.Proxy(228)
267.java.io.EOFException(227)
268.java.sql.Statement(226)
269.android.widget.ImageButton(222)
270.java.io.RandomAccessFile(220)
271.android.content.res.Configuration(220)
272.javax.sql.DataSource(219)
273.android.widget.CheckBox(217)
274.com.google.common.collect.Lists(216)
275.android.app.Application(215)
276.org.xml.sax.helpers.DefaultHandler(214)
277.java.util.concurrent.atomic.AtomicReference(214)
278.javax.xml.transform.dom.DOMSource(213)
279.javax.persistence.Entity(213)
280.android.preference.Preference(213)
281.android.app.Notification(212)
282.org.codehaus.jackson.map.ObjectMapper(212)
283.javax.swing.JOptionPane(212)
284.android.os.SystemClock(212)
285.org.springframework.beans.factory.annotation.Autowired(211)
286.java.lang.reflect.InvocationHandler(211)
287.javax.servlet.FilterChain(210)
288.java.util.SortedMap(209)
289.android.os.Parcelable(207)
290.android.app.NotificationManager(207)
291.org.springframework.context.ApplicationContext(204)
292.javax.persistence.Id(203)
293.android.view.MenuInflater(203)
294.java.awt.BorderLayout(203)
295.android.widget.ProgressBar(202)
296.java.awt.event.MouseEvent(202)
297.java.sql.DriverManager(201)
298.org.apache.http.params.HttpParams(201)
299.android.graphics.Typeface(200)
300.java.util.jar.JarFile(200)
301.java.util.concurrent.ThreadFactory(199)
302.java.awt.Component(196)
303.android.graphics.drawable.BitmapDrawable(195)
304.java.util.concurrent.Executor(194)
305.java.lang.reflect.ParameterizedType(194)
306.javax.servlet.Filter(192)
307.javax.servlet.FilterConfig(192)
308.javax.swing.JButton(192)
309.android.content.pm.PackageInfo(191)
310.java.util.concurrent.TimeoutException(190)
311.java.util.Scanner(188)
312.org.apache.commons.codec.binary.Base64(188)
313.android.widget.FrameLayout(188)
314.java.util.jar.JarEntry(187)
315.java.util.zip.ZipFile(187)
316.java.awt.Graphics2D(186)
317.java.awt.Font(186)
318.java.awt.Graphics(185)
319.java.lang.ref.SoftReference(185)
320.java.security.cert.X509Certificate(184)
321.java.security.Principal(184)
322.javax.naming.NamingException(184)
323.android.webkit.WebView(183)
324.android.view.animation.Animation(183)
325.android.content.res.TypedArray(181)
326.java.util.concurrent.locks.Lock(181)
327.javax.xml.parsers.SAXParserFactory(181)
328.javax.swing.JScrollPane(181)
329.org.testng.annotations.Test(180)
330.java.util.concurrent.ScheduledExecutorService(179)
331.java.util.MissingResourceException(178)
332.android.view.ContextMenu.ContextMenuInfo(178)
333.javax.xml.transform.TransformerException(178)
334.com.google.common.collect.Maps(178)
335.android.content.ActivityNotFoundException(177)
336.android.widget.CompoundButton(177)
337.android.os.Parcel(176)
338.javax.net.ssl.SSLContext(175)
339.android.view.animation.AnimationUtils(174)
340.org.apache.http.Header(174)
341.android.content.pm.ResolveInfo(172)
342.java.security.cert.CertificateException(171)
343.java.sql.Timestamp(171)
344.java.security.AccessController(171)
345.java.awt.event.WindowEvent(171)
346.android.content.SharedPreferences.Editor(170)
347.java.awt.event.KeyEvent(169)
348.android.graphics.RectF(169)
349.android.view.ViewGroup.LayoutParams(169)
350.org.w3c.dom.NamedNodeMap(169)
351.java.lang.management.ManagementFactory(168)
352.org.xmlpull.v1.XmlPullParserException(168)
353.javax.servlet.http.Cookie(168)
354.android.os.Looper(166)
355.org.xmlpull.v1.XmlPullParser(166)
356.java.util.concurrent.locks.ReentrantReadWriteLock(166)
357.javax.xml.bind.annotation.XmlRootElement(166)
358.java.util.concurrent.ConcurrentLinkedQueue(164)
359.android.widget.ListAdapter(164)
360.javax.swing.JTextField(164)
361.java.util.BitSet(163)
362.javax.xml.parsers.SAXParser(163)
363.java.util.concurrent.ThreadPoolExecutor(163)
364.javax.servlet.ServletConfig(163)
365.java.util.zip.ZipInputStream(162)
366.android.net.ConnectivityManager(162)
367.java.beans.PropertyChangeListener(161)
368.org.osgi.framework.Bundle(159)
369.javax.naming.InitialContext(159)
370.java.awt.Image(158)
371.org.apache.http.params.BasicHttpParams(158)
372.javax.persistence.EntityManager(158)
373.java.util.zip.ZipOutputStream(157)
374.java.security.PrivilegedAction(157)
375.java.nio.CharBuffer(157)
376.javax.swing.ImageIcon(157)
377.java.beans.PropertyDescriptor(157)
378.javax.xml.bind.JAXBContext(153)
379.com.google.common.base.Function(153)
380.javax.management.ObjectName(153)
381.org.apache.http.client.ClientProtocolException(152)
382.android.widget.Spinner(152)
383.android.content.DialogInterface.OnClickListener(152)
384.javax.persistence.GeneratedValue(151)
385.javax.swing.SwingUtilities(151)
386.javax.xml.namespace.QName(151)
387.android.os.RemoteException(150)
388.org.eclipse.swt.SWT(150)
389.android.text.Editable(150)
390.org.eclipse.swt.widgets.Composite(149)
391.org.mockito.Mockito(149)
392.org.springframework.core.io.Resource(149)
393.android.content.ContentProvider(149)
394.android.graphics.Matrix(149)
395.android.widget.RelativeLayout(148)
396.javax.servlet.ServletOutputStream(148)
397.com.google.common.collect.Sets(147)
398.org.apache.http.message.BasicNameValuePair(147)
399.java.util.EventListener(147)
400.javax.xml.transform.OutputKeys(146)
401.java.awt.Point(146)
402.java.beans.PropertyChangeEvent(146)
403.android.provider.BaseColumns(145)
404.javax.swing.JComponent(145)
405.org.apache.http.NameValuePair(144)
406.javax.swing.BorderFactory(144)
407.org.joda.time.DateTime(144)
408.javax.persistence.Column(144)
409.javax.ws.rs.Path(143)
410.org.apache.http.util.EntityUtils(143)
411.java.io.DataInput(143)
412.javax.annotation.PostConstruct(143)
413.org.xml.sax.XMLReader(143)
414.org.apache.http.params.HttpConnectionParams(142)
415.org.junit.Rule(142)
416.org.apache.commons.httpclient.HttpClient(142)
417.javax.xml.bind.annotation.XmlElement(142)
418.android.util.DisplayMetrics(141)
419.javax.xml.transform.stream.StreamSource(141)
420.android.media.AudioManager(140)
421.android.content.pm.ActivityInfo(140)
422.org.eclipse.ui.plugin.AbstractUIPlugin(139)
423.com.google.inject.Inject(139)
424.java.security.KeyStore(139)
425.org.springframework.test.context.ContextConfiguration(139)
426.com.google.common.base.Preconditions(139)
427.javax.net.ssl.TrustManager(139)
428.javax.naming.Context(138)
429.org.apache.hadoop.conf.Configuration(138)
430.java.io.FilterInputStream(138)
431.org.osgi.framework.BundleActivator(138)
432.android.view.ViewConfiguration(138)
433.android.database.SQLException(138)
434.javax.servlet.ServletContextEvent(138)
435.android.util.TypedValue(138)
436.