String a = String.valueOf(2);//integer to numeric string 

Int i = Integer.parseInt(a);//numeric string to an int

BufferedWriter out = null;

      try{

            out = new BufferedWriter(new FileWriter(”filename”,true));

            Out.write(”aString”);

      }catch(IOException e) {

         // error processing code

      }finally{

        if(out != null) {

        out.close();

      }

}

String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();

java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); 

SimpleDateFormat format =new SimpleDateFormat("dd.MM.yyyy");

Date date = format.parse( myString );

Public class OracleJdbcTest {

     String driverClass ="oracle.jdbc.driver.OracleDriver";

     Connection con;

     Public void init(FileInputStream fs) throws  ClassNotFoundException,SQLException, FileNotFoundException, IOException {

        Properties props = new Properties();

        props.load(fs);

        String url = props.getProperty("db.url");

        String userName = props.getProperty("db.user");

        String password = props.getProperty("db.password");

        Class.forName(driverClass);

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

    }

    Public void fetch() throws SQLException, IOException {

        PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");

        ResultSet rs = ps.executeQuery();

        while(rs.next()) {

        // do the thing you do

        }

        rs.close();

        ps.close();

    }

    Public static void main(String[] args) {

        OracleJdbcTest test = new OracleJdbcTest();

        test.init();

        test.fetch();

    }

}

java.util.Date utilDate = new java.util.Date();

java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());

public static void fileCopy( File in, File out ) throws IOException {

    FileChannel inChannel = new FileInputStream( in ).getChannel();

    FileChannel outChannel = new FileOutputStream( out ).getChannel();

    try {

        // inChannel.transferTo(0, inChannel.size(), outChannel);

        // original -- apparently has trouble copying large files on Windows

        // magic number for Windows, 64Mb - 32Kb)

        int maxCount = (64*1024*1024) - (32*1024);

        long size = inChannel.size();

        long position = 0;

        while( position < size ) {

        position += inChannel.transferTo( position, maxCount, outChannel );

    }

}

finally {

    if( inChannel !=null) {

        inChannel.close();

    }

    if( outChannel !=null) {

        outChannel.close();

    }

}

}
    

    private void create Thumbnail(String filename,int thumbWidth,int thumbHeight,int quality, String outFilename)

 throws InterruptedException, FileNotFoundException, IOException {

    // load image from filename

    Image image = Toolkit.getDefaultToolkit().getImage(filename);

    MediaTracker mediaTracker = new MediaTracker(newContainer());

    mediaTracker.addImage(image,0);

    mediaTracker.waitForID(0);

    // use this to test for errors at this point:             System.out.println(mediaTracker.isErrorAny());

    // determine thumbnail size from WIDTH and HEIGHT

     double thumbRatio = (double)thumbWidth / (double)thumbHeight;

    int imageWidth = image.getWidth(null);

    int imageHeight = image.getHeight(null);

    double imageRatio = (double)imageWidth / (double)imageHeight;

    if(thumbRatio < imageRatio) {

        thumbHeight = (int)(thumbWidth / imageRatio);

    }else{

        thumbWidth = (int)(thumbHeight * imageRatio);

    }

    // draw original image to thumbnail image object and

    // scale it to the new size on-the-fly

    BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);

    Graphics2D graphics2D = thumbImage.createGraphics();

　　 graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);

    graphics2D.drawImage(image,0,0, thumbWidth, thumbHeight,null);

    // save thumbnail image to outFilename

    BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFilename));

    JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);

    JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);

    quality = Math.max(0, Math.min(quality,100));

    param.setQuality((float)quality /100.0f,false);

    encoder.setJPEGEncodeParam(param);

    encoder.encode(thumbImage);

    out.close();

} 

import org.json.JSONObject;

    ...

    ...

    JSONObject json =new JSONObject();

    json.put("city","Mumbai");

    json.put("country","India");

    ...

    String output = json.toString();

    ...

import java.io.File;

import java.io.FileOutputStream;

import java.io.OutputStream;

import java.util.Date;

import com.lowagie.text.Document;

import com.lowagie.text.Paragraph;

import com.lowagie.text.pdf.PdfWriter;

public class GeneratePDF {

    public static void main(String[] args) {

        try{

            OutputStream file  = new FileOutputStream(newFile("C:\\Test.pdf"));

            Document document = new Document();

            PdfWriter.getInstance(document, file);

            document.open();

            document.add(new Paragraph("Hello Kiran"));

            document.add(new Paragraph(newDate().toString()));

            document.close();

            file.close();

        } catch(Exception e) {

            e.printStackTrace();

        }

    }

}

System.getProperties().put("http.proxyHost","someProxyURL");

System.getProperties().put("http.proxyPort","someProxyPort");

System.getProperties().put("http.proxyUser","someUserName");

System.getProperties().put("http.proxyPassword","somePassword");

public class SimpleSingleton {

    private static SimpleSingleton singleInstance = new SimpleSingleton(){

    //Marking default constructor private

    //to avoid direct instantiation. 

    private SimpleSingleton() {

    }

    //Get instance for class SimpleSingleton

    public static SimpleSingleton getInstance() {

    return singleInstance;

    }

}

public enum SimpleSingleton {

  INSTANCE;

  public void doSomething() {

 } 
}

//Call the method from Singleton:

SimpleSingleton.INSTANCE.doSomething();

import java.awt.Dimension;

import java.awt.Rectangle;

import java.awt.Robot;

import java.awt.Toolkit;

import java.awt.image.BufferedImage;

import javax.imageio.ImageIO;

import java.io.File;

...

public void captureScreen(String fileName)throws Exception {

 Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

 Rectangle screenRectangle = new Rectangle(screenSize);

 Robot robot = new Robot();

 BufferedImage image = robot.createScreenCapture(screenRectangle);

 ImageIO.write(image,"png",newFile(fileName));

} 

File dir = new File("directoryName");

String[] children = dir.list();

if(children == null) {

// Either dir does not exist or is not a directory

else{

　　for(int i = 0; i < children.length; i++) {

 　　// Get filename of file or directory 
　　String filename = children[i];

　　}

}

 // It is also possible to filter the list of returned files.

 // This example does not return any files that start with `.’.

 FilenameFilter filter = new FilenameFilter() {

 public boolean accept(File dir, String name) {

　　return !name.startsWith(".");

　　}

};

children = dir.list(filter);

// The list of files can also be retrieved as File objects

File[] files = dir.listFiles();

// This filter only returns directories

FileFilter fileFilter = new FileFilter() {

　　public boolean accept(File file) {

　　return file.isDirectory();

　　}

};

files = dir.listFiles(fileFilter);

import java.util.zip.*;

import java.io.*;

public class ZipIt {

　　public static void main(String args[]) throws IOException {

　　　　if(args.length < 2) {

　　　　　　System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");

　　　　　　System.exit(-1);

　　　　}

　　　　File zipFile = new File(args[0]);

　　　　if(zipFile.exists()) {

　　　　　　System.err.println("Zip file already exists, please try another");

　　　　　　System.exit(-2);

　　　　}

　　　　FileOutputStream fos = new FileOutputStream(zipFile);

　　　　ZipOutputStream zos = new ZipOutputStream(fos);

　　　　int bytesRead;

　　　　byte[] buffer = new byte[1024];

　　　　CRC32 crc = new CRC32();

　　　　for(int i = 1, n = args.length; i < n; i++) {

　　　　String name = args[i];

　　　　File file = new File(name);

　　　　if(!file.exists()) {

　　　　　　System.err.println("Skipping: "+ name);

　　　　　　continue;

　　　　}

　　　　BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));

　　　　crc.reset();

　　　　while((bytesRead = bis.read(buffer)) != -1) {

　　　　　　crc.update(buffer,0, bytesRead);

　　　　}

　　　　bis.close();

　　　　// Reset to beginning of input stream

　　　　bis = new BufferedInputStream(

　　　　new FileInputStream(file));

　　　　ZipEntry entry = new ZipEntry(name);

　　　　entry.setMethod(ZipEntry.STORED);

　　　　entry.setCompressedSize(file.length());

　　　　entry.setSize(file.length());

　　　　entry.setCrc(crc.getValue());

　　　　zos.putNextEntry(entry);

　　　　while((bytesRead = bis.read(buffer)) != -1) {

　　　　zos.write(buffer,0, bytesRead);

　　}

　　bis.close();

　}

　zos.close();

 } 
}

XML文件:

<?xml version="1.0"?>

    <students>

        <student>

 　　　　　　<name>John</name>

　　　　　　<grade>B</grade>

　　　　　　<age>12</age>

　　　　　</student>

　　　　　<student>

　　　　　　<name>Mary</name>

　　　　　　<grade>A</grade>

　　　　　　<age>11</age>

　　　　　</student>

　　　　  <student>

　　　　　　<name>Simon</name>

　　　　　　<grade>A</grade>

　　　　　　<age>18</age>

　　　　　</student>

　　　</students>
    

//Java代码

package net.viralpatel.java.xmlparser;

import java.io.File;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.Node;

import org.w3c.dom.NodeList;

public class XMLParser {

 public void getAllUserNames(String fileName) {

 　　try {

 　　　　DocumentBuilderFactory dbf = DocumentBuilderFactory.new Instance();

 　　　　DocumentBuilder db = dbf.new DocumentBuilder();

 　　　　File file = new File(fileName);

 　　　　if(file.exists()) {

 　　　　Document doc = db.parse(file);

 　　　　Element docEle = doc.getDocumentElement();

 　　　　// Print root element of the document

 　　　　System.out.println("Root element of the document: " + docEle.getNodeName());

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

 　　　　// Print total student elements in document

 　　　　System.out .println("Total students: "+ studentList.getLength());

 　　　　if(studentList !=null&& studentList.getLength() >0) {

 　　　　for(inti =0; i < studentList.getLength(); i++) {

 　　　　Node node = studentList.item(i);

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

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

 　　　　Element e = (Element) node;

 　　　　NodeList nodeList = e.getElementsByTagName("name");

 　　　　System.out.println("Name: " + nodeList.item(0).getChildNodes().item(0).getNodeValue());

 　　　　nodeList = e.getElementsByTagName("grade");

 　　　　System.out.println("Grade: "+ nodeList.item(0).getChildNodes().item(0).getNodeValue());

 　　　　nodeList = e.getElementsByTagName("age");

 　　　　System.out.println("Age: "+ nodeList.item(0).getChildNodes().item(0).getNodeValue());

 　　　}

 　　}

   } else {

 　　System.exit(1);

 　　}

 　}

 } catch (Exception e) {

 　　System.out.println(e);

  }

 }

 public static void main(String[] args) {

 XMLParser parser = new XMLParser();

 parser.getAllUserNames("c:\\test.xml");

  } 
} 

import java.util.Map;

import org.apache.commons.lang.ArrayUtils;

public class Main {

  public static void main(String[] args) {

  String[ ][ ] countries = { {"United States","New York"}, {"United Kingdom","London"}, {"Netherland","Amsterdam"}, {"Japan","Tokyo"},{"France","Paris"} };

  Map countryCapitals = ArrayUtils.toMap(countries);

  System.out.println("Capital of Japan is "+ countryCapitals.get("Japan"));

  System.out.println("Capital of France is "+ countryCapitals.get("France"));

 }

}

import javax.mail.*;

import javax.mail.internet.*;

import java.util.*;

public void postMail(String recipients[ ],String subject,String message,String from)throws MessagingException {

　　booleandebug =false;

　　//Set the host smtp address

　　Properties props = new Properties();

　　props.put("mail.smtp.host","smtp.example.com");

　　// create some properties and get the default Session

　　Session session = Session.getDefaultInstance(props,null);

　　session.setDebug(debug);

　　// create a message

　　Message msg = new MimeMessage(session);

　　// set the from and to address

　　InternetAddress addressFrom = new InternetAddress(from);

　　msg.setFrom(addressFrom);

　　InternetAddress[] addressTo = new InternetAddress[recipients.length];

　　for(inti =0; i < recipients.length; i++){

　　　　addressTo[i] = new InternetAddress(recipients[i]);

　　}

　　msg.setRecipients(Message.RecipientType.TO, addressTo);

　　// Optional : You can also set your custom headers in the Email if you Want

　　msg.addHeader("MyHeaderName","myHeaderValue");

　　// Setting the Subject and Content Type

　　msg.setSubject(subject);

　　msg.setContent(message,"text/plain");

　　Transport.send(msg);

}

import java.io.BufferedReader;

import java.io.InputStreamReader;

import java.net.URL;

public class Main {

  public static void main(String[] args) {

    try{

 　　URL my_url = new URL("http://cocre.com/");

 　　BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));

 　　String strTemp ="";

 　　while(null != (strTemp = br.readLine())){

 　　System.out.println(strTemp);

 　}

 }catch(Exception ex) {

 　　ex.printStackTrace();

 　}

 }

}

/**

* Reallocates an array with a new size, and copies the contents

* of the old array to the new array.

* @param oldArray the old array, to be reallocated.

* @param newSize the new array size.

* @return A new array with the same contents.

*/

private static Object resizeArray(Object oldArray,int newSize) {

 　　int oldSize = java.lang.reflect.Array.getLength(oldArray);

 　　Class elementType = oldArray.getClass().getComponentType();

 　　Object newArray = java.lang.reflect.Array.newInstance(elementType,newSize);

 　　int preserveLength = Math.min(oldSize,newSize);

 　　if(preserveLength > 0)

 　　System.arraycopy (oldArray,0,newArray,0,preserveLength);

 　　return newArray;

　}

　// Test routine for resizeArray().

  public static void main (String[] args) {

 　　int[] a = {1,2,3};

 　　a = (int[])resizeArray(a,5);

 　　a[3] =4;

 　　a[4] =5;

 　　for(inti=0; i<a.length; i++)

 　　System.out.println (a[i]);

}