java - 稍后如何在循环中使用变量

Question

我不确定这是否可能，而且我很新，所以希望你们中的一些人可以对此有所了解，我有一个函数可以读取 txt 文件的所有内容，然后在终端窗口中打印出来，但是我希望能够将文本文件的数据存储在变量中，以便我稍后可以使用它，这可能吗

这是代码片段:

String mText; 
        while((mText = br.readLine()) != null) { 
            //Displays the contents of the file in terminal
            System.out.println(mText); 
        } 

因为据我了解，一旦循环完成，变量 mText 的内容在这种情况下就会被删除？

好的，因为在下面的代码中，我想打印到打印机，该文件的内容，但是当我运行它时，我可以很好地显示文件的内容，但它永远不会出现打印机选项框，我认为这会是问题所在，看起来它是我的代码中的其他内容:

import java.awt.*;
import java.awt.font.*;
import java.awt.geom.*;
import java.awt.print.*;
import java.text.*;
import java.io.*;
import javax.swing.*;

public class PrintText implements Printable {
    private static String mText;

    // Below the code will allow the user to select a file and then print out the contents of the file
    public static void main(String[] args) throws IOException {

        //selects the file
        JFileChooser chooser = new JFileChooser();
        chooser.showOpenDialog(null);
        File file = chooser.getSelectedFile();
        String filename = file.getName();
        //System.out.println("You have selected: " + filename);  testing to see if file seleected was right
        String path = file.getAbsolutePath();

        //Reads contents of file into terminal 
        //FileReader fr = new FileReader("filename");
        // FileReader fr = new FileReader("D:/Documents/" + "filename")); 

        FileReader fr = new FileReader(path); 
        BufferedReader br = new BufferedReader(fr); 
        String mText; 
        while((mText = br.readLine()) != null) { 
            //Displays the contents of the file in terminal
            System.out.println(mText); 
        } 
        //fr.close(); 
    } 

    //private static final String mText = 
    //    "This is a test to see if this text will be printed "; //This works perfectly fine

    AttributedString mStyledText = new AttributedString(mText);


    /**
     * Print a single page containing some sample text.
     */
    static public void printer(String args[]) {
        /* Get the representation of the current printer and 
         * the current print job.
         */
        PrinterJob printerJob = PrinterJob.getPrinterJob();
        /* Build a book containing pairs of page painters (Printables)
         * and PageFormats. This example has a single page containing
         * text.
         */
        Book book = new Book();
        book.append(new PrintText(), new PageFormat());
        /* Set the object to be printed (the Book) into the PrinterJob.
         * Doing this before bringing up the print dialog allows the
         * print dialog to correctly display the page range to be printed
         * and to dissallow any print settings not appropriate for the
         * pages to be printed.
         */
        printerJob.setPageable(book);
        /* Show the print dialog to the user. This is an optional step
         * and need not be done if the application wants to perform
         * 'quiet' printing. If the user cancels the print dialog then false
         * is returned. If true is returned we go ahead and print.
         */
        boolean doPrint = printerJob.printDialog();
        if (doPrint) {
            try {
                printerJob.print();
            } catch (PrinterException exception) {
                System.err.println("Printing error: " + exception);
            }
        }
    }

    /**
     * Print a page of text.
     */
    public int print(Graphics g, PageFormat format, int pageIndex) {
        /* We'll assume that Jav2D is available.
         */
        Graphics2D g2d = (Graphics2D) g;
        /* Move the origin from the corner of the Paper to the corner
         * of the imageable area.
         */
        g2d.translate(format.getImageableX(), format.getImageableY());
        /* Set the text color.
         */
        g2d.setPaint(Color.black);
        /* Use a LineBreakMeasurer instance to break our text into
         * lines that fit the imageable area of the page.
         */
        Point2D.Float pen = new Point2D.Float();
        AttributedCharacterIterator charIterator = mStyledText.getIterator();
        LineBreakMeasurer measurer = new LineBreakMeasurer(charIterator, g2d.getFontRenderContext());
        float wrappingWidth = (float) format.getImageableWidth();
        while (measurer.getPosition() < charIterator.getEndIndex()) {
            TextLayout layout = measurer.nextLayout(wrappingWidth);
            pen.y += layout.getAscent();
            float dx = layout.isLeftToRight()? 0 : (wrappingWidth - layout.getAdvance());
            layout.draw(g2d, pen.x + dx, pen.y);
            pen.y += layout.getDescent() + layout.getLeading();
        }
        return Printable.PAGE_EXISTS;
    }
}

这是我完成的原始代码，它打印出程序中预先输入的文本，我尝试按照上面的方式添加文件阅读器，但现在它不起作用

import java.awt.*;
import java.awt.font.*;
import java.awt.geom.*;
import java.awt.print.*;
import java.text.*;
import java.io.*;
import javax.swing.*;
import java.util.List;
import java.util.ArrayList;

public class PrintText implements Printable {
   /** private static String mText;

    // Below the code will allow the user to select a file and then print out the contents of the file
    public static void main(String[] args) throws IOException {

        //selects the file
        JFileChooser chooser = new JFileChooser();
        chooser.showOpenDialog(null);
        File file = chooser.getSelectedFile();
        String filename = file.getName();
        //System.out.println("You have selected: " + filename);  testing to see if file seleected was right
        String path = file.getAbsolutePath();

        //Reads contents of file into terminal 
        //FileReader fr = new FileReader("filename");
        // FileReader fr = new FileReader("D:/Documents/" + "filename")); 

        FileReader fr = new FileReader(path); 
        BufferedReader br = new BufferedReader(fr); 
        List<String> list = new ArrayList<String>();
        while((mText = br.readLine()) != null) { 
            //Displays the contents of the file in terminal
            System.out.println(mText);
            list.add(mText); 
        } 
        //fr.close(); 
    } 
*/
    private static final String mText = 
        "This is a test to see if this text will be printed "; //This works perfectly fine

    AttributedString mStyledText = new AttributedString(mText);

    /**
     * Print a single page containing some sample text.
     */
    static public void main(String args[]) {
        /* Get the representation of the current printer and 
         * the current print job.
         */
        PrinterJob printerJob = PrinterJob.getPrinterJob();
        /* Build a book containing pairs of page painters (Printables)
         * and PageFormats. This example has a single page containing
         * text.
         */
        Book book = new Book();
        book.append(new PrintText(), new PageFormat());
        /* Set the object to be printed (the Book) into the PrinterJob.
         * Doing this before bringing up the print dialog allows the
         * print dialog to correctly display the page range to be printed
         * and to dissallow any print settings not appropriate for the
         * pages to be printed.
         */
        printerJob.setPageable(book);
        /* Show the print dialog to the user. This is an optional step
         * and need not be done if the application wants to perform
         * 'quiet' printing. If the user cancels the print dialog then false
         * is returned. If true is returned we go ahead and print.
         */
        boolean doPrint = printerJob.printDialog();
        if (doPrint) {
            try {
                printerJob.print();
            } catch (PrinterException exception) {
                System.err.println("Printing error: " + exception);
            }
        }
    }

    /**
     * Print a page of text.
     */
    public int print(Graphics g, PageFormat format, int pageIndex) {
        /* We'll assume that Jav2D is available.
         */
        Graphics2D g2d = (Graphics2D) g;
        /* Move the origin from the corner of the Paper to the corner
         * of the imageable area.
         */
        g2d.translate(format.getImageableX(), format.getImageableY());
        /* Set the text color.
         */
        g2d.setPaint(Color.black);
        /* Use a LineBreakMeasurer instance to break our text into
         * lines that fit the imageable area of the page.
         */
        Point2D.Float pen = new Point2D.Float();
        AttributedCharacterIterator charIterator = mStyledText.getIterator();
        LineBreakMeasurer measurer = new LineBreakMeasurer(charIterator, g2d.getFontRenderContext());
        float wrappingWidth = (float) format.getImageableWidth();
        while (measurer.getPosition() < charIterator.getEndIndex()) {
            TextLayout layout = measurer.nextLayout(wrappingWidth);
            pen.y += layout.getAscent();
            float dx = layout.isLeftToRight()? 0 : (wrappingWidth - layout.getAdvance());
            layout.draw(g2d, pen.x + dx, pen.y);
            pen.y += layout.getDescent() + layout.getLeading();
        }
        return Printable.PAGE_EXISTS;
    }
}

Answer 1

as i understand it once the loop finishes the contents of the variable mText in this case gets deleted ?

如果您正在从文本文件中读取多行，则之前的所有写入都会被以下写入覆盖。所以，你的变量 mText将仅包含读取的最后一行。

如果您希望在循环结束后可以访问所有读取的行，您可以将这些行存储在某个集合中。

理想情况下，您可以创建 List<String>在这种情况下，并将您的数据存储在其中:-

List<String> list = new ArrayList<String>();
while((mText = br.readLine()) != null) { 
        //Displays the contents of the file in terminal
        System.out.println(mText);
        list.add(mText); 
} 

现在，在 while 循环之外，您可以从列表中访问数据。