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我需要在 pdf 文件中找到(光栅)图像并调整它们的大小(改变他们的分辨率)。
我的代码基于示例 PrintImageLocations。对于部分有效,我扩展了 PDFStreamEngine 并对“Do”运算符:
我使用第一个参数获取原始 PDImageXObject运营商和资源。
然后我从中创建一个 BufferedImage 并对其进行处理以更改像素数。
然后我通过 BufferedImage 创建一个新的 PDImageXObject无损工厂
最后我使用以下方法将新对象放入页面资源中原始对象的名称
我尝试对内嵌图像做类似的事情,然后我得到了我有一个 BufferedImage,但我不知道如何使用它替换原来的内嵌图像。
用 XObject 替换内联图像也可以,但是再说一遍,我不知道如何替换两者......
下面是我的代码;有趣的部分是函数“processOperator”。
// WIP!
// find raster images inside a pdf
// if their resolution is more than 900dpi
// then resize them
// reducing the resolution to 200dpi
// NB bug: fails on pdf files with more than one page
// ...DEBUG ScratchFileBuffer:516 - ScratchFileBuffer not closed!
// also fails on pdf with included pdf
// (e.g. latex \includegraphics{x.pdf})
// # to compile:
// apt install libpdfbox2-java
// export CLASSPATH=.:/usr/share/java/pdfbox2.jar:/usr/share/java/commons-logging.jar
// javac Resampleimages.java
// # to run:
// java Resampleimages x.pdf
// see
// https://pdfbox.apache.org/2.0/examples.html
// https://pdfbox.apache.org/docs/2.0.11/javadocs/
import org.apache.pdfbox.cos.COSBase;
import org.apache.pdfbox.cos.COSName;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.graphics.PDXObject;
import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;
import org.apache.pdfbox.pdmodel.graphics.image.PDImage;
import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
import org.apache.pdfbox.pdmodel.graphics.image.PDInlineImage;
import org.apache.pdfbox.util.Matrix;
import org.apache.pdfbox.contentstream.operator.DrawObject;
import org.apache.pdfbox.contentstream.operator.Operator;
import org.apache.pdfbox.contentstream.PDFStreamEngine;
import org.apache.pdfbox.pdmodel.PDResources;
import org.apache.pdfbox.pdmodel.graphics.image.LosslessFactory;
import java.io.File;
import java.io.IOException;
import java.util.List;
import java.awt.image.BufferedImage;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Color;
import org.apache.pdfbox.contentstream.operator.state.Concatenate;
import org.apache.pdfbox.contentstream.operator.state.Restore;
import org.apache.pdfbox.contentstream.operator.state.Save;
import org.apache.pdfbox.contentstream.operator.state.SetGraphicsStateParameters;
import org.apache.pdfbox.contentstream.operator.state.SetMatrix;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
public class ReplaceBigImages extends PDFStreamEngine
{
private static Log log = LogFactory.getLog(ReplaceBigImages.class);
public ReplaceBigImages() throws IOException
{
addOperator(new Concatenate());
addOperator(new DrawObject());
addOperator(new SetGraphicsStateParameters());
addOperator(new Save());
addOperator(new Restore());
addOperator(new SetMatrix());
}
public static PDDocument document;
public static void main( String[] args ) throws IOException
{
if( args.length != 1 )
{
usage();
}
else
{
try
{
document = PDDocument.load(new File(args[0]));
ReplaceBigImages printer = new ReplaceBigImages();
int pageNum = 0;
for( PDPage page : document.getPages() )
{
pageNum++;
log.info( "Processing page: " + pageNum );
printer.processPage(page);
}
}
finally {
if( document != null )
{
document.save(args[0].replace(".pdf", "_test.pdf"));
document.close();
}
}
}
}
protected void processOperator( Operator operator, List<COSBase> operands) throws IOException
{
String operation = operator.getName();
// log.debug(String.format("Operator %s", operation));
if( "Do".equals(operation) ) {
log.debug("### Found Do operator");
COSName objectName = (COSName) operands.get( 0 );
PDXObject xobject = getResources().getXObject( objectName );
// log.debug(String.format("%s isa %s", objectName, xobject.getClass().getSimpleName()));
if( xobject instanceof PDImageXObject)
{
log.debug(String.format("Looking at %s (%s)", objectName.getName(), xobject));
PDImageXObject image = (PDImageXObject)xobject;
BufferedImage scaledImage = changeImageResolution(image);
if (scaledImage != null) {
log.debug(String.format("Replacing with %s", scaledImage));
PDImageXObject replacement_img = LosslessFactory.createFromImage(document, scaledImage);
PDPage currentPage = getCurrentPage();
PDResources resources = currentPage.getResources();
resources.put(objectName, replacement_img);
}
}else if(xobject instanceof PDFormXObject)
{
PDFormXObject form = (PDFormXObject)xobject;
showForm(form);
}
} else if ("BI".equals(operation)) {
PDPage currentPage = getCurrentPage();
log.debug("### Found BI operator");
PDResources resources = currentPage.getResources();
PDInlineImage image = new PDInlineImage(operator.getImageParameters(),
operator.getImageData(),
resources);
BufferedImage scaledImage = changeImageResolution(image);
if (scaledImage != null) {
log.debug(String.format("Replacing with %s", scaledImage));
PDImageXObject replacement_img = LosslessFactory.createFromImage(document, scaledImage);
// ARGH!!! How do I replace the inline image???
resources.add(replacement_img, "pippo");
// operator.setImageParameters(scaledImage???)
// operator.setImageData(scaledImage???)
}
} else {
super.processOperator( operator, operands);
}
}
protected BufferedImage changeImageResolution( PDImage image)
throws IOException
{
int imageWidth = image.getWidth();
int imageHeight = image.getHeight();
Matrix ctmNew = getGraphicsState().getCurrentTransformationMatrix();
float imageXScale = Math.abs(ctmNew.getScalingFactorX());
float imageYScale = Math.abs(ctmNew.getScalingFactorY());
float resolution = imageWidth / ( imageXScale / 72 );
String stencil = "";
if (image.isStencil()) {
stencil = " (stencil)";
}
// TODO: take into consideration the size at which this file is included by TeX
log.debug("size: ("+imageWidth+","+imageHeight+")@("+imageXScale+","+imageYScale+") resolution = "+resolution+stencil);
// if ( resolution > 899f ) {
if ( resolution > 200f ) {
// what do the following two lines mean???
BufferedImage bImage = new BufferedImage(imageWidth,
imageHeight,
BufferedImage.TYPE_INT_ARGB);
if (image.isStencil()) {
log.warn("Is stencil; painting black.");
bImage = image.getStencilImage(Color.black);
} else {
bImage = image.getImage();
}
int desiredResolution = 200;
float xFactor = (imageXScale / 72) * desiredResolution / imageWidth;
float yFactor = (imageYScale / 72) * desiredResolution / imageHeight;
log.info("Scaling x to "+xFactor);
int dWidth = (int) (xFactor * imageWidth);
int dHeight = (int) (yFactor * imageHeight);
// the image type is from
// https://docs.oracle.com/javase/6/docs/api/constant-values.html#java.awt.image.
log.debug(String.format("Destination: %d x %d [%s]",
dWidth,
dHeight,
bImage.getType()));
BufferedImage scaledImage = new BufferedImage(dWidth,
dHeight,
bImage.getType());
Graphics2D graphics2D = scaledImage.createGraphics();
graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BILINEAR);
graphics2D.setRenderingHint(RenderingHints.KEY_RENDERING,
RenderingHints.VALUE_RENDER_QUALITY);
graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
graphics2D.drawImage(bImage, 0, 0, dWidth, dHeight, null);
graphics2D.dispose();
// see https://pdfbox.apache.org/docs/2.0.11/javadocs/org/apache/pdfbox/pdmodel/graphics/image/PDImageXObject.html#createFromByteArray-org.apache.pdfbox.pdmodel.PDDocument-byte:A-java.lang.String-
return scaledImage;
}
return null;
}
private static void usage()
{
System.err.println( "Usage: java " + ReplaceBigImages.class.getName() + " <input-pdf>" );
}
}
最佳答案
在 Tilman Hausherr(详细信息 here )的(很多)帮助下,我想我有一段代码可以调整 InlineImages 和 XObjects 的大小。下面代码中的方法是:
这是代码:
package it.sissa.medialab.pdfimages;
// Find raster images inside a pdf
// if their resolution is outside of a given threshold
// then resize them
// reducing the resolution to a given target resolution.
// If the pdf will be included inside another pdf
// (as with TeX \includegraphics)
// one can provide a --scale factor
// Usage
// -----
// java -Dlog4j.configurationFile=/tmp/log4j.xml \
// it/sissa/medialab/pdfimages/ReplaceBigImages \
// --scale=XXX -v \
// pesky-file.pdf
// CLASSPATH
// ---------
// This script uses pdfbox, picocli (for the command line), commons-io, commons-logging and log4j
// So the CLASSPATH could be:
// export CLASSPATH=$HOME/.m2/repository/org/apache/pdfbox/pdfbox/2.0.14/pdfbox-2.0.14.jar:$HOME/.m2/repository/commons-logging/commons-logging/1.2/commons-logging-1.2.jar:$HOME/.m2/repository/commons-io/commons-io/2.6/commons-io-2.6.jar:$HOME/.m2/repository/info/picocli/picocli/3.9.5/picocli-3.9.5.jar:$HOME/.m2/repository/org/apache/logging/log4j/log4j-api/2.11.2/log4j-api-2.11.2.jar:$HOME/.m2/repository/org/apache/logging/log4j/log4j-core/2.11.2/log4j-core-2.11.2.jar:$HOME/typeset/scripts/pdfimages/target/classes/
// log4j.xml (example)
//
// <?xml version="1.0" encoding="UTF-8"?>
// <Configuration status="info" strict="true" name="XMLConfigTest" packages="org.apache.logging.log4j.test">
// <Appenders>
// <Appender type="Console" name="STDOUT">
// <Layout type="PatternLayout" pattern="%-5p %c{1}:%L %M - %m%n"/>
// </Appender>
// </Appenders>
// <Loggers>
// <Logger name="pippo"
// level="info"
// additivity="false">
// <AppenderRef ref="STDOUT"/>
// </Logger>
// <Root level="info">
// <AppenderRef ref="STDOUT"/>
// </Root>
// </Loggers>
// </Configuration>
// export CLASSPATH=$HOME/.m2/repository/org/apache/pdfbox/pdfbox/2.0.14/pdfbox-2.0.14.jar:$HOME/.m2/repository/commons-logging/commons-logging/1.2/commons-logging-1.2.jar:$HOME/.m2/repository/commons-io/commons-io/2.6/commons-io-2.6.jar:$HOME/.m2/repository/info/picocli/picocli/3.9.5/picocli-3.9.5.jar:$HOME/.m2/repository/org/apache/logging/log4j/log4j-api/2.11.2/log4j-api-2.11.2.jar:$HOME/.m2/repository/org/apache/logging/log4j/log4j-core/2.11.2/log4j-core-2.11.2.jar:./target/classes
// java -Dlog4j.configurationFile=log4j.xml it/sissa/medialab/pdfimages/ReplaceBigImages --max=220 --min=200 -v --target=220 src/resources/META-INF/test-files/d.pdf
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.LinkedBlockingQueue;
import javax.imageio.ImageIO;
import org.apache.commons.io.IOUtils;
import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.config.Configurator;
import org.apache.pdfbox.contentstream.PDFStreamEngine;
import org.apache.pdfbox.contentstream.operator.DrawObject;
import org.apache.pdfbox.contentstream.operator.Operator;
import org.apache.pdfbox.contentstream.operator.state.Concatenate;
import org.apache.pdfbox.contentstream.operator.state.Restore;
import org.apache.pdfbox.contentstream.operator.state.Save;
import org.apache.pdfbox.contentstream.operator.state.SetGraphicsStateParameters;
import org.apache.pdfbox.contentstream.operator.state.SetMatrix;
import org.apache.pdfbox.cos.COSBase;
import org.apache.pdfbox.cos.COSName;
import org.apache.pdfbox.pdfparser.PDFStreamParser;
import org.apache.pdfbox.pdfwriter.ContentStreamWriter;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDResources;
import org.apache.pdfbox.pdmodel.common.PDStream;
import org.apache.pdfbox.pdmodel.graphics.PDXObject;
import org.apache.pdfbox.pdmodel.graphics.color.PDDeviceGray;
import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;
import org.apache.pdfbox.pdmodel.graphics.image.LosslessFactory;
import org.apache.pdfbox.pdmodel.graphics.image.PDImage;
import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
import org.apache.pdfbox.pdmodel.graphics.image.PDInlineImage;
import org.apache.pdfbox.util.Matrix;
import picocli.CommandLine;
import picocli.CommandLine.Command;
import picocli.CommandLine.Option;
import picocli.CommandLine.Parameters;
@Command(description = "Resample raster images in the given pdf file when their resolution is outside the given min-max range.",
name = "pdfimage",
mixinStandardHelpOptions = true,
version = "pdfimages 1.2")
public class ReplaceBigImages
extends PDFStreamEngine
implements Runnable
{
// private static Log log = LogFactory.getLog(ReplaceBigImages.class);
private static Logger log = LogManager.getLogger(ReplaceBigImages.class);
public boolean hasInlineImages = false;
public LinkedBlockingQueue<Matrix> tms = new LinkedBlockingQueue<Matrix>();
@Parameters(paramLabel = "FILE", description = "File to process.")
private File inputFile;
@Option(names = "--min", description = "Resolution lower bound; defaults to 150", required = false)
private float min_res=150;
@Option(names = "--max", description = "Resolution upper bound; defaults to 220", required = false)
private float max_res=220;
@Option(names = "--target", description = "Desired resolution (only if the current resolution exeedes the bounds). Defaults to 220", required = false)
private int desiredResolution = 220;
@Option(names = "--scale", description = "Scale factor. The options min, max and target will be multiplied by this factor. This should be the same scale at which the pdf \"image\" under analysis will be included by the tex file into the final pdf. See 00-readme.txt. Defaults to 1.0", required = false)
private float scale=1;
@Option(names = { "-v", "--verbose" }, description = "Be verbose.")
private boolean verbose = false;
private int myCounter = 0;
public ReplaceBigImages() throws IOException
{
addOperator(new Concatenate());
addOperator(new DrawObject());
addOperator(new SetGraphicsStateParameters());
addOperator(new Save());
addOperator(new Restore());
addOperator(new SetMatrix());
}
@Override
public void run() {
if (verbose) {
if (log instanceof Logger) {
// https://stackoverflow.com/a/44678752/1581629
Configurator.setLevel(LogManager.getLogger(ReplaceBigImages.class).getName(), Level.DEBUG);
} else {
log.warn("Unknown logger " + log.getClass().toString() + "; ignoring option \"verbose\".");
log.warn("I only know about " + Logger.class.toString());
}
}
min_res = (float) (min_res * scale);
max_res = (float) (max_res * scale);
desiredResolution = (int) (desiredResolution * scale);
try {
document = PDDocument.load(inputFile);
int pageNum = 0;
for (PDPage page : document.getPages()) {
pageNum++;
log.info("Processing page: " + pageNum);
processPage(page);
if (hasInlineImages) {
replaceInlineImages(document, page, tms.remove());
}
}
} catch (Exception e) {
log.error(e);
} finally {
if (document != null) {
log.debug("Ready to save");
try {
document.save(inputFile.toPath().toString().replace(".pdf", "-m.pdf"));
log.debug("Document saved");
document.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public static PDDocument document;
public static void main( String[] args ) throws IOException
{
ReplaceBigImages app = new ReplaceBigImages();
CommandLine.run(app, args);
}
protected void processOperator( Operator operator, List<COSBase> operands) throws IOException
{
String operation = operator.getName();
if( "Do".equals(operation) ) {
log.debug("### Found Do operator");
COSName objectName = (COSName) operands.get( 0 );
PDXObject xobject = getResources().getXObject( objectName );
if( xobject instanceof PDImageXObject)
{
log.debug(String.format("Looking at %s (%s)", objectName.getName(), xobject));
PDImageXObject image = (PDImageXObject)xobject;
Matrix ctmNew = getGraphicsState().getCurrentTransformationMatrix();
BufferedImage scaledImage = changeImageResolution(image, ctmNew);
if (scaledImage != null) {
log.debug(String.format("Replacing with %s", scaledImage));
PDImageXObject replacement_img = LosslessFactory.createFromImage(document, scaledImage);
replacement_img.setStencil(image.isStencil());
PDPage currentPage = getCurrentPage();
PDResources resources = currentPage.getResources();
resources.put(objectName, replacement_img);
}
} else if(xobject instanceof PDFormXObject)
{
PDFormXObject form = (PDFormXObject)xobject;
showForm(form);
}
} else if ("BI".equals(operation)) {
hasInlineImages = true;
// save the current transformation matrix
// I will need it later, to compute the resolution of the inline image
Matrix ctmNew = getGraphicsState().getCurrentTransformationMatrix();
tms.add(ctmNew);
} else {
super.processOperator( operator, operands);
}
}
protected void replaceInlineImages (PDDocument document, PDPage page, Matrix ctm) throws Exception {
// take the content stream of the current page,
// parse it, get a list of tokens
// run through the list of tokens
// and build a new list
// when a BI operator is found,
// change the resolution of the relative inline image
// and replace the "BI" operator with the new one
PDFStreamParser parser = new PDFStreamParser(page);
parser.parse();
List<Object> tokens = parser.getTokens();
List<Object> newTokens = new ArrayList<Object>();
for(int j=0; j<tokens.size(); j++) {
Object token = tokens.get( j );
if( token instanceof Operator ) {
Operator operator = (Operator)token;
if("BI".equals(operator.getName())) {
log.debug("### Found BI operator");
// NB: there is not trace of ID or EI operators in the original token list
// so just replacing the BI should replace the whole block BI-ID-EI
PDResources resources = page.getResources();
PDInlineImage image = new PDInlineImage(operator.getImageParameters(),
operator.getImageData(),
resources);
BufferedImage scaledImage = changeImageResolution(image, ctm);
if (scaledImage != null) {
log.debug(String.format("Replacing with %s", scaledImage));
PDImageXObject helper_img = LosslessFactory.createFromImage(document, scaledImage);
helper_img.setStencil(image.isStencil());
InputStream img_data_stream = helper_img.getCOSObject().createRawInputStream();
byte [] img_data = IOUtils.toByteArray(img_data_stream);
img_data_stream.close();
Operator newBIoperator = Operator.getOperator("BI");
newBIoperator.setImageParameters(helper_img.getCOSObject());
newBIoperator.setImageData(img_data);
newTokens.add(newBIoperator);
continue;
}
}
}
newTokens.add( token );
}
// use newTokens to build a new stream
PDStream newContents = new PDStream( document );
OutputStream outputStream = newContents.createOutputStream();
ContentStreamWriter writer = new ContentStreamWriter( outputStream );
writer.writeTokens( newTokens );
page.setContents( newContents );
outputStream.close();
log.debug("New contents set for page");
}
protected BufferedImage changeImageResolution( PDImage image, Matrix ctmNew)
throws IOException
{
int imageWidth = image.getWidth();
int imageHeight = image.getHeight();
float imageXScale = Math.abs(ctmNew.getScalingFactorX());
float imageYScale = Math.abs(ctmNew.getScalingFactorY());
float resolution = imageWidth / (imageXScale / 72);
int bufferedImageType = BufferedImage.TYPE_INT_RGB;
String stencil = "";
if (image.isStencil()) {
stencil = " (stencil)";
bufferedImageType = BufferedImage.TYPE_BYTE_BINARY;
} else if (image.getColorSpace() == PDDeviceGray.INSTANCE) {
bufferedImageType = BufferedImage.TYPE_BYTE_GRAY;
}
// TODO: take into consideration the size at which this file is included by TeX
log.debug("Original size: (" + imageWidth + "," + imageHeight + ")@scale(" + imageXScale + "," + imageYScale
+ "); resolution = (" + min_res + "<)" + resolution + "(<" + max_res + ")" + stencil);
if (resolution > max_res || resolution < min_res) {
BufferedImage bImage = new BufferedImage(imageWidth, imageHeight, bufferedImageType);
bImage.setData(image.getImage().getData());
// do not do "bImage = image.getImage()" or the image type will be wrong
if (image.isStencil()) {
log.warn("Image is stencil, plese check.");
// bImage = image.getStencilImage(Color.red);
// ↑ No: see https://lists.apache.org/thread.html/8d6477f6e057b83ab34655041045dc9e0288b4eeba6d65b52a92ab52@%3Cusers.pdfbox.apache.org%3E
}
if (log.isDebugEnabled()) {
myCounter += 1;
log.debug("Saving original img to \"original-"+myCounter+".png\"");
File outputfile = new File("original-"+myCounter+".png");
ImageIO.write(bImage, "png", outputfile);
}
if (desiredResolution == -1) {
desiredResolution = (int) ((max_res + min_res) / 2.0);
}
float xFactor = (imageXScale / 72) * desiredResolution / imageWidth;
float yFactor = (imageYScale / 72) * desiredResolution / imageHeight;
log.info("Scaling x by factor " + xFactor + " (desired resolution is " + desiredResolution + ")");
int dWidth = (int) (xFactor * imageWidth);
int dHeight = (int) (yFactor * imageHeight);
// the image type is from
// https://docs.oracle.com/javase/6/docs/api/constant-values.html#java.awt.image.
log.debug(String.format("Destination: %d x %d [%s]", dWidth, dHeight, bImage.getType()));
BufferedImage scaledImage = new BufferedImage(dWidth, dHeight, bImage.getType());
Graphics2D graphics2D = scaledImage.createGraphics();
graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
graphics2D.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
graphics2D.drawImage(bImage, 0, 0, dWidth, dHeight, null);
graphics2D.dispose();
if (log.isDebugEnabled()) {
log.debug("Saving scaled img to \"scaled-"+myCounter+".png\"");
File outputfile = new File("scaled-"+myCounter+".png");
ImageIO.write(scaledImage, "png", outputfile);
}
return scaledImage;
}
return null;
}
/**
* @return the hasInlineImages
*/
public boolean isHasInlineImages() {
return hasInlineImages;
}
/**
* @param hasInlineImages the hasInlineImages to set
*/
public void setHasInlineImages(boolean hasInlineImages) {
this.hasInlineImages = hasInlineImages;
}
/**
* @return the tms
*/
public LinkedBlockingQueue<Matrix> getTms() {
return tms;
}
/**
* @param tms the tms to set
*/
public void setTms(LinkedBlockingQueue<Matrix> tms) {
this.tms = tms;
}
}
关于java - 用 pdfbox 替换 PDF 中的内嵌图像,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/54744038/
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我的 friend 给了我一个谜语让我解开。它是这样的: There are 100 people. Each one of them, in his turn, does the following
如果我将使用 Java 5 代码的应用程序编译成字节码,生成的 .class 文件是否能够在 Java 1.4 下运行? 如果后者可以工作并且我正在尝试在我的 Java 1.4 应用程序中使用 Jav
有关于why Java doesn't support unsigned types的问题以及一些关于处理无符号类型的问题。我做了一些搜索,似乎 Scala 也不支持无符号数据类型。限制是Java和S
我只是想知道在一个 java 版本中生成的字节码是否可以在其他 java 版本上运行 最佳答案 通常,字节码无需修改即可在 较新 版本的 Java 上运行。它不会在旧版本上运行,除非您使用特殊参数 (
我有一个关于在命令提示符下执行 java 程序的基本问题。 在某些机器上我们需要指定 -cp 。 (类路径)同时执行java程序 (test为java文件名与.class文件存在于同一目录下) jav
我已经阅读 StackOverflow 有一段时间了,现在我才鼓起勇气提出问题。我今年 20 岁,目前在我的家乡(罗马尼亚克卢日-纳波卡)就读 IT 大学。足以介绍:D。 基本上,我有一家提供簿记应用
我有 public JSONObject parseXML(String xml) { JSONObject jsonObject = XML.toJSONObject(xml); r
我已经在 Java 中实现了带有动态类型的简单解释语言。不幸的是我遇到了以下问题。测试时如下代码: def main() { def ks = Map[[1, 2]].keySet()
一直提示输入 1 到 10 的数字 - 结果应将 st、rd、th 和 nd 添加到数字中。编写一个程序,提示用户输入 1 到 10 之间的任意整数,然后以序数形式显示该整数并附加后缀。 public
我有这个 DownloadFile.java 并按预期下载该文件: import java.io.*; import java.net.URL; public class DownloadFile {
我想在 GUI 上添加延迟。我放置了 2 个 for 循环,然后重新绘制了一个标签,但这 2 个 for 循环一个接一个地执行,并且标签被重新绘制到最后一个。 我能做什么? for(int i=0;
我正在对对象 Student 的列表项进行一些测试,但是我更喜欢在 java 类对象中创建硬编码列表,然后从那里提取数据,而不是连接到数据库并在结果集中选择记录。然而,自从我这样做以来已经很长时间了,
我知道对象创建分为三个部分: 声明 实例化 初始化 classA{} classB extends classA{} classA obj = new classB(1,1); 实例化 它必须使用
我有兴趣使用 GPRS 构建车辆跟踪系统。但是,我有一些问题要问以前做过此操作的人: GPRS 是最好的技术吗?人们意识到任何问题吗? 我计划使用 Java/Java EE - 有更好的技术吗? 如果
我可以通过递归方法反转数组,例如:数组={1,2,3,4,5} 数组结果={5,4,3,2,1}但我的结果是相同的数组,我不知道为什么,请帮助我。 public class Recursion { p
有这样的标准方式吗? 包括 Java源代码-测试代码- Ant 或 Maven联合单元持续集成(可能是巡航控制)ClearCase 版本控制工具部署到应用服务器 最后我希望有一个自动构建和集成环境。
我什至不知道这是否可能,我非常怀疑它是否可能,但如果可以,您能告诉我怎么做吗?我只是想知道如何从打印机打印一些文本。 有什么想法吗? 最佳答案 这里有更简单的事情。 import javax.swin
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