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20个JAVA人员非常有用的功能代码

来源：互联网 发布：2017年进出口贸易数据 编辑：程序博客网 时间：2024/05/02 03:01
本文将为大家介绍20人员非常有用的Java功能代码。这20段代码，可以成为大家在今后的开发过程中，Java编程手册的重要部分。

1. 把Strings转换成int和把int转换成String
  1. String a = String.valueOf(2);   //integer to numeric string
  2. int i = Integer.parseInt(a); //numeric string to an int
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2. 向Java文件中添加文本
  1. Updated: Thanks Simone for pointing to exception. I have 

  3. changed the code.  

  5. BufferedWriter out = null;
  6. try {
  7. out = new BufferedWriter(new FileWriter(”filename”, true));
  8. out.write(”aString”);
  9. } catch (IOException e) {
  10. // error processing code
  11. } finally {
  12. if (out != null) {
  13. out.close();
  14. }
  15. }
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3. 获取Java现在正调用的方法名 
  1. String methodName = Thread.currentThread().getStackTrace()[1].getMethodName ();
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4. 在Java中将String型转换成Date型
  1. java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);  
  2. or 
  3. SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );  
  4. Date date = format.parse( myString );
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5. 通过Java JDBC链接Oracle数据库
  1. public class OracleJdbcTest
  2. {
  3. String driverClass = "oracle.jdbc.driver.OracleDriver";

  5. Connection con;

  7. public void init(FileInputStream fs) throws ClassNotFoundException,

  9. SQLException, FileNotFoundException, IOException
  10. {
  11. Properties props = new Properties();
  12. props.load (fs);
  13. String url = props.getProperty ("db.url");
  14. String userName = props.getProperty ("db.user");
  15. String password = props.getProperty ("db.password");
  16. Class.forName(driverClass);

  18. con=DriverManager.getConnection(url, userName, password);
  19. }

  21. public void fetch() throws SQLException, IOException
  22. {
  23. PreparedStatement ps = con.prepareStatement("select SYSDATE from

  25. dual");
  26. ResultSet rs = ps.executeQuery();

  28. while (rs.next())
  29. {
  30. // do the thing you do
  31. }
  32. rs.close();
  33. ps.close ();
  34. }

  36. public static void main(String[] args)
  37. {
  38. OracleJdbcTest test = new OracleJdbcTest ();
  39. test.init();
  40. test.fetch();
  41. }
  42. }
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6.将Java中的util.Date转换成sql.Date
这一片段显示如何将一个java util Date转换成sql Date用于数据库
  1. java.util.Date utilDate = new java.util.Date();
  2. java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
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7. 使用NIO快速复制Java文件
  1. public static void fileCopy( File in, File out )
  2. throws IOException
  3. {
  4. FileChannel inChannel = new FileInputStream( in ).getChannel ();
  5. FileChannel outChannel = new FileOutputStream( out ).getChannel();
  6. try
  7. {
  8. //          inChannel.transferTo (0, inChannel.size(), outChannel);      // original

  10. -- apparently has trouble copying large files on Windows

  12. // magic number for Windows, 64Mb - 32Kb)
  13. int maxCount = (64 * 1024 * 1024) - (32 * 1024);
  14. long size = inChannel.size ();
  15. long position = 0;
  16. while ( position < size )
  17. {
  18.   position += inChannel.transferTo( position, maxCount, outChannel );
  19. }
  20. }
  21. finally
  22. {
  23. if ( inChannel != null )
  24. {
  25.   inChannel.close ();
  26. }
  27. if ( outChannel != null )
  28. {
  29.    outChannel.close ();
  30. }
  31. }
  32. }
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8. 在Java中创建缩略图
  1. private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)
  2. throws InterruptedException, FileNotFoundException, IOException
  3. {
  4. // load image from filename
  5. Image image = Toolkit.getDefaultToolkit().getImage (filename);
  6. MediaTracker mediaTracker = new MediaTracker(new Container());
  7. mediaTracker.addImage(image, 0);
  8. mediaTracker.waitForID(0);
  9. // use this to test for errors at this point: System.out.println

  11. (mediaTracker.isErrorAny());

  13. // determine thumbnail size from WIDTH and HEIGHT
  14. double thumbRatio = (double)thumbWidth / (double) thumbHeight;
  15. int imageWidth = image.getWidth (null);
  16. int imageHeight = image.getHeight (null);
  17. double imageRatio = (double)imageWidth / (double) imageHeight;
  18. if (thumbRatio < imageRatio) {
  19. thumbHeight = (int)(thumbWidth / imageRatio);
  20. } else {
  21. thumbWidth = (int) (thumbHeight * imageRatio);
  22. }

  24. // draw original image to thumbnail image object and
  25. // scale it to the new size on-the- fly
  26. BufferedImage thumbImage = new BufferedImage(thumbWidth,

  28. thumbHeight, BufferedImage.TYPE_INT_RGB);
  29. Graphics2D graphics2D = thumbImage.createGraphics();
  30. graphics2D.setRenderingHint (RenderingHints.KEY_INTERPOLATION,

  32. RenderingHints.VALUE_INTERPOLATION_BILINEAR);
  33. graphics2D.drawImag e(image, 0, 0, thumbWidth, thumbHeight, null);

  35. // save thumbnail image to outFilename
  36. BufferedOutputStream out = new BufferedOutputStream(new

  38. FileOutputStream(outFilename));
  39. JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
  40. JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam

  42. (thumbImage);
  43. quality = Math.max(0, Math.min(quality, 100));
  44. param.setQuality((float)quality / 100.0f, false);
  45. encoder.setJPEGEncodeParam (param);
  46. encoder.encode(thumbImage);
  47. out.close ();
  48. }
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9. 在Java中创建JSON数据
  1. Read this article for more details.
  2. Download JAR file json
  3. -rpc-1.0.jar (75 kb)
  4. import org.json.JSONObject;
  5. ...
  6. ...
  7. JSONObject json = new JSONObject();
  8. json.put("city", "Mumbai");
  9. json.put("country", "India");
  10. ...
  11. String output = json.toString();
  12. ...
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10. 在Java中使用iText JAR打开PDF
  1. Read this article for more details.

  3. import java.io.File;
  4. import java.io.FileOutputStream;
  5. import java.io.OutputStream;
  6. import java.util.Date;

  8. import com.lowagie.text.Document;
  9. import com.lowagie.text.Paragraph;
  10. import com.lowagie.text.pdf.PdfWriter;

  12. public class GeneratePDF {

  14. public static void main(String[] args) {
  15. try {
  16. OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));

  18. Document document = new Document ();
  19. PdfWriter.getInstance(document, file);
  20. document.open ();
  21. document.add(new Paragraph("Hello Kiran"));
  22. document.add(new Paragraph(new Date().toString()));

  24. document.close ();
  25. file.close();

  27. } catch (Exception e) {

  29. e.printStackTrace();
  30. }
  31. }
  32. }
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11. 在Java上的HTTP代理设置 
  1. System.getProperties().put("http.proxyHost", "someProxyURL");
  2. System.getProperties().put("http.proxyPort", "someProxyPort");
  3. System.getProperties().put("http.proxyUser", "someUserName");
  4. System.getProperties().put("http.proxyPassword", "somePassword");
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12. Java Singleton 例子
  1. Read this article for more
  2. details.
  3. Update: Thanks Markus for the comment. I have updated the code and
  4. changed it to
  5. more robust implementation.


  8. public class SimpleSingleton {
  9. private static SimpleSingleton singleInstance =  new SimpleSingleton();

  11. //Marking default constructor private
  12. //to avoid direct instantiation.
  13. private SimpleSingleton() {
  14. }

  16. //Get instance for class SimpleSingleton
  17. public static SimpleSingleton getInstance() {

  19. return singleInstance;
  20. }
  21. }
  22. One more implementation of Singleton class. Thanks to Ralph and Lukasz Zielinski

  24. for pointing this out.


  27. public enum SimpleSingleton {
  28. INSTANCE;
  29. public void doSomething() {
  30. }
  31. }

  33. //Call the method from Singleton:
  34. SimpleSingleton.INSTANCE.doSomething();
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13. 在Java上做屏幕截图
  1. Read this article for more details.


  4. import java.awt.Dimension;
  5. import java.awt.Rectangle;
  6. import java.awt.Robot;
  7. import java.awt.Toolkit;
  8. import java.awt.image.BufferedImage;
  9. import javax.imageio.ImageIO;
  10. import java.io.File;

  12. ...

  14. public void captureScreen(String fileName) throws Exception {

  16. Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize ();
  17. Rectangle screenRectangle = new Rectangle (screenSize);
  18. Robot robot = new Robot();
  19. BufferedImage image = robot.createScreenCapture(screenRectangle);
  20. ImageIO.write(image, "png", new File(fileName));

  22. }
  23. ...
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14. 在Java中的文件，目录列表
  1. File dir = new File("directoryName");
  2. String[] children = dir.list();
  3. if (children == null) {
  4. // Either dir does not exist or is not a directory
  5. } else {
  6. for (int i=0; i < children.length; i++) {
  7. // Get filename of file or directory
  8. String filename = children;
  9. }
  10. }

  12. // It is also possible to filter the list of returned files.
  13. // This example does not return any files that start with `.'.
  14. FilenameFilter filter = new FilenameFilter() {
  15. public boolean accept(File dir, String name) {
  16. return ! name.startsWith(".");
  17. }
  18. };
  19. children = dir.list(filter);

  21. // The list of files can also be retrieved as File objects
  22. File[] files = dir.listFiles();

  24. // This filter only returns directories
  25. FileFilter fileFilter = new FileFilter() {
  26. public boolean accept(File file) {
  27. return file.isDirectory();
  28. }
  29. };
  30. files = dir.listFiles (fileFilter);
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15. 在Java中创建ZIP和JAR文件
  1. import java.util.zip.*;
  2. import java.io.*;

  4. public class ZipIt {
  5. public static void main(String args []) throws IOException {
  6. if (args.length < 2) {
  7. System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");
  8. System.exit(-1);
  9. }
  10. File zipFile = new File(args [0]);
  11. if (zipFile.exists()) {
  12. System.err.println("Zip file already exists, please try another");
  13. System.exit(-2);
  14. }
  15. FileOutputStream fos = new FileOutputStream(zipFile);
  16. ZipOutputStream zos = new ZipOutputStream (fos);
  17. int bytesRead;
  18. byte[] buffer = new byte [1024];
  19. CRC32 crc = new CRC32 ();
  20. for (int i=1, n=args.length; i < n; i++) {
  21. String name = args;
  22. File file = new File (name);
  23. if (!file.exists()) {
  24.    System.err.println("Skipping: " + name);
  25. & nbsp;   continue;
  26. }
  27. BufferedInputStream bis = new BufferedInputStream (
  28.    new FileInputStream (file));
  29. crc.reset();
  30. while ((bytesRead = bis.read(buffer)) != -1) {
  31.    crc.update(buffer, 0, bytesRead);
  32. }
  33. bis.close ();
  34. // Reset to beginning of input stream
  35. bis = new BufferedInputStream (
  36.    new FileInputStream (file));
  37. ZipEntry entry = new ZipEntry (name);
  38. entry.setMethod (ZipEntry.STORED);
  39. & nbsp; entry.setCompressedSize(file.length ());
  40. entry.setSize(file.length ());
  41. entry.setCrc(crc.getValue ());
  42. zos.putNextEntry (entry);
  43. while ((bytesRead = bis.read(buffer)) != -1) {
  44.    zos.write(buffer, 0, bytesRead);
  45. }
  46. bis.close ();
  47. }
  48. zos.close();
  49. }
  50. }
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16. Parsing / Reading XML file in Java
  1. Sample XML file.
  2. //...

  4. package net.viralpatel.java.xmlparser;

  6. import java.io.File;
  7. import javax.xml.parsers.DocumentBuilder;
  8. import javax.xml.parsers.DocumentBuilderFactory;

  10. import org.w3c.dom.Document;
  11. import org.w3c.dom.Element;
  12. import org.w3c.dom.Node;
  13. import org.w3c.dom.NodeList;

  15. public class XMLParser {

  17. public void getAllUserNames(String fileName) {
  18. try {
  19. DocumentBuilderFactory dbf =

  21. DocumentBuilderFactory.newInstance();
  22. DocumentBuilder db = dbf.newDocumentBuilder();
  23. File file = new File (fileName);
  24. if (file.exists()) {
  25. Document doc = db.parse (file);
  26. Element docEle = doc.getDocumentElement();

  28. // Print root element of the document
  29. System.out.println("Root element of the document: "
  30. + docEle.getNodeName());

  32. NodeList studentList = docEle.getElementsByTagName

  34. ("student");

  36. // Print total student elements in document
  37. System.out
  38. &nb sp;.println("Total students: " +

  40. studentList.getLength());

  42. if (studentList != null && studentList.getLength()

  44. > 0) {
  45. for (int i = 0; i < studentList.getLength

  47. (); i++) {

  49. Node node = studentList.item(i);

  51. if (node.getNodeType() ==

  53. Node.ELEMENT_NODE) {

  55. System.out
  56.      .println

  58. ("=====================");

  60. Element e = (Element) node;
  61. NodeList nodeList =

  63. e.getElementsByTagName ("name");
  64. System.out.println("Name: "
  65. +

  67. nodeList.item(0).getChildNodes().item(0)

  69. .getNodeValue());

  71. nodeList =

  73. e.getElementsByTagName ("grade");
  74. System.out.println("Grade:

  76. "
  77. +

  79. nodeList.item(0).getChildNodes().item(0)

  81. .getNodeValue());

  83. nodeList =

  85. e.getElementsByTagName ("age");
  86. System.out.println("Age: "
  87. +

  89. nodeList.item(0).getChildNodes().item(0)

  91. .getNodeValue());
  92. }
  93. }
  94. } else {
  95. System.exit(1);
  96. }
  97. }
  98. } catch (Exception e) {
  99. System.out.println(e);
  100. }
  101. }
  102. public static void main(String[] args) {

  104. XMLParser parser = new XMLParser ();
  105. parser.getAllUserNames("c:\\test.xml");
  106. }
  107. }
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17. Convert Array to Map in Java
  1. import java.util.Map;
  2. import org.apache.commons.lang.ArrayUtils;

  4. public class Main {

  6. public static void main(String[] args) {
  7. String[][] countries = { { "United States", "New York" }, { "United Kingdom",

  9. "London" },
  10. { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" }

  12. };

  14. Map countryCapitals = ArrayUtils.toMap(countries);

  16. System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
  17. System.out.println("Capital of France is " + countryCapitals.get("France"));
  18. }
  19. }
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18. Send Email using Java

  2. import javax.mail.*;
  3. import javax.mail.internet.*;
  4. import java.util.*;

  6. public void postMail( String recipients[ ], String subject, String message , String

  8. from) throws MessagingException
  9. {
  10. boolean debug = false;

  12. //Set the host smtp address
  13. Properties props = new Properties();
  14. props.put ("mail.smtp.host", "smtp.example.com");

  16. // create some properties and get the default Session
  17. Session session = Session.getDefaultInstance(props, null);
  18. session.setDebug(debug);

  20. // create a message
  21. Message msg = new MimeMessage(session);

  23. // set the from and to address
  24. InternetAddress addressFrom = new InternetAddress(from);
  25. msg.setFrom(addressFrom);

  27. InternetAddress[] addressTo = new InternetAddress [recipients.length];
  28. for (int i = 0; i < recipients.length; i++)
  29. {
  30. addressTo = new InternetAddress (recipients);
  31. }
  32. msg.setRecipients (Message.RecipientType.TO, addressTo);

  34. // Optional : You can also set your custom headers in the Email if you Want
  35. msg.addHeader("MyHeaderName", "myHeaderValue");

  37. // Setting the Subject and Content Type
  38. msg.setSubject(subject);
  39. msg.setContent(message, "text/plain");
  40. Transport.send(msg);
  41. }
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19. Send HTTP request & fetching data using Java
  1. import java.io.BufferedReader;
  2. import java.io.InputStreamReader;
  3. import java.net.URL;

  5. public class Main {
  6. public static void main(String[] args)  {
  7. try {
  8. URL my_url = new URL("http://www.viralpatel.net/blogs/");
  9.    BufferedReader br = new BufferedReader(new

  11. InputStreamReader(my_url.openStream()));
  12. String strTemp = "";
  13. while(null != (strTemp = br.readLine())) {
  14. System.out.println(strTemp);
  15. }
  16. } catch (Exception ex) {
  17. ex.printStackTrace ();
  18. }
  19. }
  20. }
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20. Resize an Array in Java
  1. /**
  2. * Reallocates an array with a new size, and copies the contents
  3. * of the old array to the new array.
  4. * @param oldArray  the old array, to be reallocated.
  5. * @param newSize   the new array size.
  6. * @return          A new array with the same contents.
  7. */
  8. private static Object resizeArray (Object oldArray, int newSize) {  
  9. int oldSize = java.lang.reflect.Array.getLength(oldArray);  
  10. Class elementType = oldArray.getClass().getComponentType();  
  11. Object newArray = java.lang.reflect.Array.newInstance(  
  12. elementType,newSize);  
  13. int preserveLength = Math.min (oldSize,newSize);  
  14. if (preserveLength > 0)   
  15. System.arraycopy (oldArray,0,newArray,0,preserveLength);  
  16. return newArray;  
  17. }  

  19. // Test routine for resizeArray().  
  20. public static void main (String[] args) {  
  21. int[] a = {1,2,3};  
  22. a = (int[])resizeArray(a,5);  
  23. a[3] = 4;  
  24. a[4] = 5;  
  25. for (int i=0; i
  26.       System.out.println (a);  
  27. } 
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16. 在Java中解析/读取XML文件
  1. view plaincopy to clipboardprint?

  3. <?xml version="1.0"?>  
  4. <students>  
  5. <student>  
  6. <name>John</name>  
  7. <grade>B</grade>  
  8. <age>12</age>  
  9. </student>  
  10. <student>  
  11. <name>Mary</name>  
  12. <grade>A</grade>  
  13. <age>11</age>  
  14. </student>  
  15. <student>  
  16. <name>Simon</name>  
  17. <grade>A</grade>  
  18. <age>18</age>  
  19. </student>  
  20. </students>  



  24. <?xml version="1.0"?>
  25. <students>
  26. <student>
  27. <name>John</name>
  28. <grade>B</grade>
  29. <age>12</age>
  30. </student>
  31. <student>
  32. <name>Mary</name>
  33. <grade>A</grade>
  34. <age>11</age>
  35. </student>
  36. <student>
  37. <name>Simon</name>
  38. <grade>A</grade>
  39. <age>18</age>
  40. </student>
  41. </students>
  42. Java code to parse above XML.

  44. view plaincopy to clipboardprint?

  46. package net.viralpatel.java.xmlparser;

  48. import java.io.File;
  49. import javax.xml.parsers.DocumentBuilder;
  50. import javax.xml.parsers.DocumentBuilderFactory;

  52. import org.w3c.dom.Document;
  53. import org.w3c.dom.Element;
  54. import org.w3c.dom.Node;
  55. import org.w3c.dom.NodeList;

  57. public class XMLParser {

  59. public void getAllUserNames(String fileName) {
  60. try {
  61. DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
  62. DocumentBuilder db = dbf.newDocumentBuilder();
  63. File file = new File(fileName);
  64. if (file.exists()) {
  65. Document doc = db.parse(file);
  66. Element docEle = doc.getDocumentElement();

  68. // Print root element of the document
  69. System.out.println("Root element of the document: "
  70. + docEle.getNodeName());

  72. NodeList studentList = docEle.getElementsByTagName("student");

  74. // Print total student elements in document
  75. System.out
  76. .println("Total students: " + studentList.getLength());

  78. if (studentList != null && studentList.getLength() > 0) {
  79. for (int i = 0; i < studentList.getLength(); i++) {

  81. Node node = studentList.item(i);

  83. if (node.getNodeType() == Node.ELEMENT_NODE) {

  85. System.out
  86. .println("=====================");

  88. Element e = (Element) node;
  89. NodeList nodeList = e.getElementsByTagName("name");
  90. System.out.println("Name: "
  91. + nodeList.item(0).getChildNodes().item(0)
  92. .getNodeValue());

  94. nodeList = e.getElementsByTagName("grade");
  95. System.out.println("Grade: "
  96. + nodeList.item(0).getChildNodes().item(0)
  97. .getNodeValue());

  99. nodeList = e.getElementsByTagName("age");
  100. System.out.println("Age: "
  101. + nodeList.item(0).getChildNodes().item(0)
  102. .getNodeValue());
  103. }
  104. }
  105. } else {
  106. System.exit(1);
  107. }
  108. }
  109. } catch (Exception e) {
  110. System.out.println(e);
  111. }
  112. }
  113. public static void main(String[] args) {

  115. XMLParser parser = new XMLParser();
  116. parser.getAllUserNames("c:\\test.xml");
  117. }
  118. }
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17. 在Java中将Array转换成Map
  1. view plaincopy to clipboardprint?

  3. import java.util.Map;
  4. import org.apache.commons.lang.ArrayUtils;

  6. public class Main {

  8. public static void main(String[] args) {
  9. String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },
  10. { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };

  12. Map countryCapitals = ArrayUtils.toMap(countries);

  14. System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
  15. System.out.println("Capital of France is " + countryCapitals.get("France"));
  16. }
  17. }
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18. 在Java中发送电子邮件
  1. view plaincopy to clipboardprint?

  3. import javax.mail.*;
  4. import javax.mail.internet.*;
  5. import java.util.*;

  7. public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
  8. {
  9. boolean debug = false;

  11. //Set the host smtp address
  12. Properties props = new Properties();
  13. props.put("mail.smtp.host", "smtp.example.com");

  15. // create some properties and get the default Session
  16. Session session = Session.getDefaultInstance(props, null);
  17. session.setDebug(debug);

  19. // create a message
  20. Message msg = new MimeMessage(session);

  22. // set the from and to address
  23. InternetAddress addressFrom = new InternetAddress(from);
  24. msg.setFrom(addressFrom);

  26. InternetAddress[] addressTo = new InternetAddress[recipients.length];
  27. for (int i = 0; i < recipients.length; i++)
  28. {
  29. addressTo = new InternetAddress(recipients);
  30. }
  31. msg.setRecipients(Message.RecipientType.TO, addressTo);

  33. // Optional : You can also set your custom headers in the Email if you Want
  34. msg.addHeader("MyHeaderName", "myHeaderValue");

  36. // Setting the Subject and Content Type
  37. msg.setSubject(subject);
  38. msg.setContent(message, "text/plain");
  39. Transport.send(msg);
  40. }
复制代码
19. 使用Java发送HTTP请求和提取数据
  1. view plaincopy to clipboardprint?

  3. import java.io.BufferedReader;
  4. import java.io.InputStreamReader;
  5. import java.net.URL;

  7. public class Main {
  8. public static void main(String[] args)  {
  9. try {
  10. URL my_url = new URL("http://www.viralpatel.net/blogs/");
  11. BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
  12. String strTemp = "";
  13. while(null != (strTemp = br.readLine())){
  14. System.out.println(strTemp);
  15. }
  16. } catch (Exception ex) {
  17. ex.printStackTrace();
  18. }
  19. }
  20. }
复制代码
20. 在Java中调整数组
  1. view plaincopy to clipboardprint?

  3. /**  
  4. * Reallocates an array with a new size, and copies the contents  
  5. * of the old array to the new array.  
  6. * @param oldArray  the old array, to be reallocated.  
  7. * @param newSize   the new array size.  
  8. * @return          A new array with the same contents.  
  9. */  
  10. private static Object resizeArray (Object oldArray, int newSize) {   
  11. int oldSize = java.lang.reflect.Array.getLength(oldArray);   
  12. Class elementType = oldArray.getClass().getComponentType();   
  13. Object newArray = java.lang.reflect.Array.newInstance(   
  14. elementType,newSize);   
  15. int preserveLength = Math.min(oldSize,newSize);   
  16. if (preserveLength > 0)   
  17. System.arraycopy (oldArray,0,newArray,0,preserveLength);   
  18. return newArray;   
  19. }   

  21. // Test routine for resizeArray().   
  22. public static void main (String[] args) {   
  23. int[] a = {1,2,3};   
  24. a = (int[])resizeArray(a,5);   
  25. a[3] = 4;   
  26. a[4] = 5;   
  27. for (int i=0; i<a.length; i++)   
  28. System.out.println (a);   

  1. } 
  2. 原文地址： http://club.topsage.com/thread-2574000-1-2.html

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