计算机二级辅导:20个非常有用的Java程序片段(1)
发布时间：2010/3/13 9:28:26 来源：城市学习网 编辑：MOON
下面是20个非常有用的Java程序片段，希望能对你有用。
Java代码
String a = String.valueOf(2); //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int
Java代码
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();
}
}
Java代码
String methodName = Thread.currentThread().getStackTrace().getMethodName();
Java代码
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
或者是：
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
Date date = format.parse( myString );
Java代码
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代码
java.util.Date utilDate = new java.util.Date();
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
Java代码
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); // originalapparently 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();
}
}
}
Java代码
private void createThumbnail(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(new Container());
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();
}
Java代码
请先阅读这篇文章 了解一些细节，
并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)
import org.json.JSONObject;
...
...
JSONObject json = new JSONObject();
json.put("city"， "Mumbai");
json.put("country"， "India");
...
String output = json.toString();
...
Java代码
阅读这篇文章 了解细节
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(new File("C:““Test.pdf"));
Document document = new Document();
PdfWriter.getInstance(document， file);
document.open();
document.add(new Paragraph("Hello Kiran"));
document.add(new Paragraph(new Date().toString()));
document.close();
file.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
Java代码
阅读这篇 文章 了解细节。
System.getProperties().put("http.proxyHost"， "someProxyURL");
System.getProperties().put("http.proxyPort"， "someProxyPort");
System.getProperties().put("http.proxyUser"， "someUserName");
System.getProperties().put("http.proxyPassword"， "somePassword");
Java代码
请先阅读这篇文章 了解信息
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;
}
}
另一种实现
public enum SimpleSingleton {
INSTANCE;
public void doSomething() {
}
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething();
Java代码
阅读这篇文章 获得信息。
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"， new File(fileName));
}
...
阅读这篇文章 获得信息。
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"， new File(fileName));
}
:
