在这篇文章中，我们将带领您了解JavaforLoop评估的全貌，包括java评价的相关情况。同时，我们还将为您介绍有关20veryusefulJavacodesnippetsforJavaDevelo
在这篇文章中，我们将带领您了解Java for Loop评估的全貌，包括java评价的相关情况。同时，我们还将为您介绍有关20 very useful Java code snippets for Java Develop、A nice tool for java developer -Thumbnailator、c# – 在foreach-loop中创建许多DropDownListFor、com.sun.tools.javac.tree.JCTree.JCEnhancedForLoop的实例源码的知识，以帮助您更好地理解这个主题。
本文目录一览：- Java for Loop评估（java评价）
- 20 very useful Java code snippets for Java Develop
- A nice tool for java developer -Thumbnailator
- c# – 在foreach-loop中创建许多DropDownListFor
- com.sun.tools.javac.tree.JCTree.JCEnhancedForLoop的实例源码
Java for Loop评估（java评价）
我想知道是否在循环周期结束时在Java中执行条件评估for并while在Java中循环。
例：
int[] tenBig = new int[]{1,2,3,4,5,6,7,8,9,10};for(int index = 0;index < tenBig.length;index++){ System.out.println("Value at index: "+tenBig[index]);}请问index < tenBig.lengthBE执行每次循环周期结束的时间？
假设和经验告诉我是的。
我知道在此示例中，它tenBig.length是一个常量，因此不会对性能产生影响。
但是让我们假设条件操作在不同情况下花费的时间很长。我知道接下来要做的逻辑就是将赋给tenBig.length变量。
我仍然要确保每次都对其进行评估。
答案1
小编典典是的，它将在每次循环迭代时逻辑上评估整个中间操作数。当然，如果JIT知道的更好，它可以做一些聪明的事情（甚至可能根据循环条件在循环中删除数组边界检查）。
请注意，对于JIT未知的类型，它可能无法像这样专门进行优化-但仍可能内联诸如获取size()of的内容ArrayList<T>。
最后，我通常更喜欢增强的for循环以提高可读性：
for (int value : tenBig) { ...}当然，这是假设您出于其他原因不需要索引。
20 very useful Java code snippets for Java Develop
1. Converting Strings to int and int to Stringview plaincopy to clipboardprint?
String a = String.valueOf(2); //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int
String a = String.valueOf(2); //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int
2. Append text to file in Java
Updated: Thanks Simone for pointing to exception. I have changed the code.
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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();
}
}
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();
}
}
3. Get name of current method in Java
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String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
4. Convert String to Date in Java
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java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
or
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SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
Date date = format.parse( myString );
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
Date date = format.parse( myString );
5. Connecting to Oracle using Java JDBC
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public class OracleJdbcTest
{
String driver;
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();
}
}
public class OracleJdbcTest
{
String driver;
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();
}
}
6. Convert Java util.Date to sql.Date
This snippet shows how to convert a java util Date into a sql Date for use in databases.
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java.util.Date utilDate = new java.util.Date();
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
java.util.Date utilDate = new java.util.Date();
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
7. Java Fast File Copy using NIO
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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();
}
}
}
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();
}
}
}
8. Create Thumbnail of an image in Java
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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();
}
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();
}
9. Creating JSON data in Java
Read this article for more details.
Download JAR file json-rpc-1.0.jar (75 kb)
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import org.json.JSONObject;
...
...
JSONObject json = new JSONObject();
json.put("city", "Mumbai");
json.put("country", "India");
...
String output = json.toString();
...
import org.json.JSONObject;
...
...
JSONObject json = new JSONObject();
json.put("city", "Mumbai");
json.put("country", "India");
...
String output = json.toString();
...
10. PDF Generation in Java using iText JAR
Read this article for more details.
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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();
}
}
}
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();
}
}
}
11. HTTP Proxy setting in Java
Read this article for more details.
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System.getProperties().put("http.proxyHost", "someProxyURL");
System.getProperties().put("http.proxyPort", "someProxyPort");
System.getProperties().put("http.proxyUser", "someUserName");
System.getProperties().put("http.proxyPassword", "somePassword");
System.getProperties().put("http.proxyHost", "someProxyURL");
System.getProperties().put("http.proxyPort", "someProxyPort");
System.getProperties().put("http.proxyUser", "someUserName");
System.getProperties().put("http.proxyPassword", "somePassword");
12. Java Singleton example
Read this article for more details.
Update: Thanks Markus for the comment. I have updated the code and changed it to more robust implementation.
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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 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;
}
}
One more implementation of Singleton class. Thanks to Ralph and Lukasz Zielinski for pointing this out.
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public enum SimpleSingleton {
INSTANCE;
public void doSomething() {
}
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething();
public enum SimpleSingleton {
INSTANCE;
public void doSomething() {
}
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething();
13. Capture screen shots in Java
Read this article for more details.
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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));
}
...
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));
}
...
14. Files-Directory listing in Java
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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);
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);
15. Creating ZIP and JAR Files in Java
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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();
}
}
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();
}
}
16. Parsing / Reading XML file in Java
Sample XML file.
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<?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>
<?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 code to parse above XML.
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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.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
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 (int i = 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");
}
}
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.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
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 (int i = 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");
}
}
17. Convert Array to Map in Java
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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 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"));
}
}
18. Send Email using Java
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import javax.mail.*;
import javax.mail.internet.*;
import java.util.*;
public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
{
boolean debug = 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 (int i = 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 javax.mail.*;
import javax.mail.internet.*;
import java.util.*;
public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
{
boolean debug = 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 (int i = 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);
}
19. Send HTTP request & fetching data using Java
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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://www.viralpatel.net/blogs/");
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();
}
}
}
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://www.viralpatel.net/blogs/");
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();
}
}
}
20. Resize an Array in Java
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/**
* 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 (int i=0; i<a.length; i++)
System.out.println (a[i]);
}
A nice tool for java developer -Thumbnailator
Create a thumbnail from an image file
Thumbnails.of(new File("original.jpg"))
.size(160, 160)
.toFile(new File("thumbnail.jpg"));
In this example, the image from original.jpg is resized, and then saved to thumbnail.jpg.
Alternatively, Thumbnailator will accept file names as a String. Using File objects to specify image files is not required:
Thumbnails.of("original.jpg")
.size(160, 160)
.toFile("thumbnail.jpg");
This form can be useful when writing quick prototype code, or when Thumbnailator is being used from scripting languages.
Create a thumbnail with rotation and a watermark
Thumbnails.of(new File("original.jpg"))
.size(160, 160)
.rotate(90)
.watermark(Positions.BOTTOM_RIGHT, ImageIO.read(new File("watermark.png")), 0.5f)
.outputQuality(0.8f)
.toFile(new File("image-with-watermark.jpg"));
In this example, the image from original.jpg is resized, then rotated to clockwise by 90 degrees, then a watermark is placed at the bottom right-hand corner which is half transparent, then is saved to image-with-watermark.jpg with 80% compression quality settings.
Create a thumbnail and write to an OutputStream
OutputStream os = ...;
Thumbnails.of("large-picture.jpg")
.size(200, 200)
.outputFormat("png")
.toOutputStream(os);
In this example, an image from the file large-picture.jpg is resized to a maximum dimension of 200 x 200 (maintaining the aspect ratio of the original image) and writes the that to the specified OutputStream as a PNG image.
Creating fixed-size thumbnails
BufferedImage originalImage = ImageIO.read(new File("original.png"));
BufferedImage thumbnail = Thumbnails.of(originalImage)
.size(200, 200)
.asBufferedImage();
The above code takes an image in originalImage and creates a 200 pixel by 200 pixel thumbnail using and stores the result in thumbnail.
Scaling an image by a given factor
BufferedImage originalImage = ImageIO.read(new File("original.png"));
BufferedImage thumbnail = Thumbnails.of(originalImage)
.scale(0.25f)
.asBufferedImage();
The above code takes the image in originalImage and creates a thumbnail that is 25% of the original image, and uses the default scaling technique in order to make the thumbnail which is stored in thumbnail.
Rotating an image when creating a thumbnail
BufferedImage originalImage = ImageIO.read(new File("original.jpg"));
BufferedImage thumbnail = Thumbnails.of(originalImage)
.size(200, 200)
.rotate(90)
.asBufferedImage();
The above code takes the original image and creates a thumbnail which is rotated clockwise by 90 degrees.
Creating a thumbnail with a watermark
BufferedImage originalImage = ImageIO.read(new File("original.jpg"));
BufferedImage watermarkImage = ImageIO.read(new File("watermark.png"));
BufferedImage thumbnail = Thumbnails.of(originalImage)
.size(200, 200)
.watermark(Positions.BOTTOM_RIGHT, watermarkImage, 0.5f)
.asBufferedImage();
As shown, a watermark can be added to an thumbnail by calling the watermark method.
c# – 在foreach-loop中创建许多DropDownListFor
参见英文答案 >
DropDownListFor does not select value if in for loop6个
> How to set default value to select list in MVC during run time2个
我想从List中动态创建DropDownLists,它提供SelectList和一个保存选择的字段.
> How to set default value to select list in MVC during run time2个
我想从List中动态创建DropDownLists,它提供SelectList和一个保存选择的字段.
public class viewmodel
{
public List<Material_Select> materialSelect { get; set; }
}
public class Material_Select
{
public SelectList selectList { get; set; }
public int MaterialId { get; set; }
}
在视图中,我想循环遍历materialSelect List并动态创建DropDownLists.
像这样的东西：
int count = 0;
foreach (var item in Model.materialSelect)
{
count++;
<div>
@Html.LabelFor(model => model.materialSelect)
</div>
<div>
@Html.DropDownListFor(item.MaterialId,item.selectList)
</div>
}
在HttpPost ActionResult我需要获取选定的值.有谁知道如何解决这个问题？
解决方法
你可能应该使用
EditorTemplates.这些允许你疯狂地做你所描述的.如果在〜/ Views / Shared / EditorTemplates / Material_Select.cshtml中创建强类型的局部视图(视图必须与模型命名相同),如下所示：
@model Material_Select
<div>
@Html.LabelFor(m => m.MaterialId)
</div>
<div>
@Html.DropDownListFor(m => m.MaterialId,Model.selectList)
</div>
然后在您的整体表格中,您可以致电：
@Html.EditorFor(m => m.materialSelect)
这将自动枚举您的集合并为集合中的每个项目呈现编辑器模板.
com.sun.tools.javac.tree.JCTree.JCEnhancedForLoop的实例源码
项目：incubator-netbeans
文件：CasualDiff.java
protected int diffForeachLoop(JCEnhancedForLoop oldT,JCEnhancedForLoop newT,int[] bounds) {
int localPointer = bounds[0];
// variable
int[] varBounds = getBounds(oldT.var);
copyTo(localPointer,varBounds[0]);
localPointer = diffTree(oldT.var,newT.var,varBounds);
// expression
int[] exprBounds = getBounds(oldT.expr);
copyTo(localPointer,exprBounds[0]);
localPointer = diffTree(oldT.expr,newT.expr,exprBounds);
// body
int[] bodyBounds = new int[] { localPointer,endPos(oldT.body) };
int oldindent = newT.body.hasTag(Tag.BLOCK) ? -1 : printer.indent();
localPointer = diffTree(oldT.body,newT.body,bodyBounds,oldT.getKind());
if (!newT.body.hasTag(Tag.BLOCK))
printer.undent(oldindent);
copyTo(localPointer,bounds[1]);
return bounds[1];
}
项目：lombok-ianchiu
文件：PrettyPrinter.java
@Override public void visitForeachLoop(JCEnhancedForLoop tree) {
aPrint("for (");
printvarDefInline(tree.var);
print(" : ");
print(tree.expr);
print(") ");
print(tree.body);
}
项目：javaparser2jctree
文件：PrintAstVisitor.java
public void visitForeachLoop(JCEnhancedForLoop that) {
try {
print("JCEnhancedForLoop:");
} catch (Exception e) {
}
super.visitForeachLoop(that);
}
项目：EasyMPermission
文件：PrettyCommentsPrinter.java
public void visitForeachLoop(JCEnhancedForLoop tree) {
try {
print("for (");
printExpr(tree.var);
print(" : ");
printExpr(tree.expr);
print(") ");
printStat(tree.body);
} catch (IOException e) {
throw new UncheckedioException(e);
}
}
项目：refactor-faster
文件：UEnhancedForLoop.java
@Override
public JCEnhancedForLoop inline(Inliner inliner) throws CouldNotResolveImportException {
return inliner.maker().ForeachLoop(
getvariable().inline(inliner),getExpression().inline(inliner),getStatement().inline(inliner));
}
项目：android-retrolambda-lombok
文件：JcTreePrinter.java
@Override public void visitForeachLoop(JCEnhancedForLoop tree) {
printNode(tree);
child("var",tree.var);
child("expr",tree.expr);
child("body",tree.body);
indent--;
}
项目：android-retrolambda-lombok
文件：JcTreeConverter.java
@Override public void visitForeachLoop(JCEnhancedForLoop node) {
ForEach fe = new ForEach();
fe.rawIterable(toTree(node.getExpression()));
fe.rawStatement(toTree(node.getStatement()));
fe.rawVariable(toTree(node.getvariable(),FlagKey.VARDEF_IS_DEFinitioN));
set(node,fe);
}
项目：error-prone
文件：UEnhancedForLoop.java
@Override
public JCEnhancedForLoop inline(Inliner inliner) throws CouldNotResolveImportException {
return inliner
.maker()
.ForeachLoop(
getvariable().inline(inliner),getStatement().inline(inliner));
}
项目：error-prone
文件：PlaceholderUnificationVisitor.java
@Override
public Choice<State<JCEnhancedForLoop>> visitEnhancedForLoop(
final EnhancedForLoopTree node,State<?> state) {
return chooseSubtrees(
state,s -> unifyExpression(node.getExpression(),s),s -> unifyStatement(node.getStatement(),(expr,stmt) -> maker().ForeachLoop((JCVariableDecl) node.getvariable(),expr,stmt));
}
项目：s4j
文件：Pretty.java
public void visitForeachLoop(JCEnhancedForLoop tree) {
try {
print("for (");
printExpr(tree.var);
print(" : ");
printExpr(tree.expr);
print(") ");
printStat(tree.body);
} catch (IOException e) {
throw new UncheckedioException(e);
}
}
项目：s4j
文件：Attr.java
public void visitForeachLoop(JCEnhancedForLoop tree) {
Env<AttrContext> loopEnv =
env.dup(env.tree,env.info.dup(env.info.scope.dup()));
attribStat(tree.var,loopEnv);
Type exprType = types.upperBound(attribExpr(tree.expr,loopEnv));
chk.checkNonVoid(tree.pos(),exprType);
Type elemtype = types.elemtype(exprType); // perhaps expr is an array?
if (elemtype == null) {
// or perhaps expr implements Iterable<T>?
Type base = types.asSuper(exprType,syms.iterableType.tsym);
if (base == null) {
log.error(tree.expr.pos(),"foreach.not.applicable.to.type",exprType,diags.fragment("type.req.array.or.iterable"));
elemtype = types.createErrorType(exprType);
} else {
List<Type> iterableParams = base.allparams();
elemtype = iterableParams.isEmpty()
? syms.objectType
: types.upperBound(iterableParams.head);
}
}
chk.checkType(tree.expr.pos(),elemtype,tree.var.sym.type);
loopEnv.tree = tree; // before,we were not in loop!
attribStat(tree.body,loopEnv);
loopEnv.info.scope.leave();
result = null;
}
项目：Refaster
文件：UEnhancedForLoop.java
@Override
public JCEnhancedForLoop inline(Inliner inliner) throws CouldNotResolveImportException {
return inliner.maker().ForeachLoop(
getvariable().inline(inliner),getStatement().inline(inliner));
}
项目：lombok
文件：PrettyCommentsPrinter.java
public void visitForeachLoop(JCEnhancedForLoop tree) {
try {
print("for (");
printExpr(tree.var);
print(" : ");
printExpr(tree.expr);
print(") ");
printStat(tree.body);
} catch (IOException e) {
throw new UncheckedioException(e);
}
}
项目：incubator-netbeans
文件：CasualDiff.java
private boolean matchForeachLoop(JCEnhancedForLoop t1,JCEnhancedForLoop t2) {
return treesMatch(t1.var,t2.var) && treesMatch(t1.expr,t2.expr) &&
treesMatch(t1.body,t2.body);
}
项目：openjdk-jdk10
文件：Analyzer.java
@Override
public void visitForeachLoop(JCEnhancedForLoop tree) {
//skip body (to prevents same statements to be analyzed twice)
scan(tree.getExpression());
}
项目：openjdk9
文件：Analyzer.java
@Override
public void visitForeachLoop(JCEnhancedForLoop tree) {
scan(tree.getExpression());
}
项目：lombok-ianchiu
文件：JavacTreeMaker.java
public JCEnhancedForLoop ForeachLoop(JCVariableDecl var,JCExpression expr,JCStatement body) {
return invoke(ForeachLoop,var,body);
}
项目：javaparser2jctree
文件：AJCEnhancedForLoop.java
public AJCEnhancedForLoop(JCEnhancedForLoop ltree) {
super(ltree.var,ltree.expr,ltree.body);
}
项目：javaparser2jctree
文件：AJCEnhancedForLoop.java
public AJCEnhancedForLoop(JCEnhancedForLoop ltree,String lcomment) {
this(ltree);
setComment(lcomment);
}
项目：EasyMPermission
文件：JavacTreeMaker.java
public JCEnhancedForLoop ForeachLoop(JCVariableDecl var,body); }
我们今天的关于Java for Loop评估和java评价的分享就到这里，谢谢您的阅读，如果想了解更多关于20 very useful Java code snippets for Java Develop、A nice tool for java developer -Thumbnailator、c# – 在foreach-loop中创建许多DropDownListFor、com.sun.tools.javac.tree.JCTree.JCEnhancedForLoop的实例源码的相关信息，可以在本站进行搜索。
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