显示行数

import java.awt.BorderLayout;

import java.awt.Color;

import java.awt.Dimension;

import java.awt.Font;

import java.awt.FontMetrics;

import java.awt.Graphics;

import java.awt.Rectangle;

import javax.swing.BorderFactory;

import javax.swing.JComponent;

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.JScrollPane;

import javax.swing.JTextArea;

public class LineNumber extends JComponent {

        static final long serialVersionUID = 3679449495322768618L;

        private final static Color DEFAULT_BACKGROUND = new Color(140,140,140);//230, 163, 4

        private final static Color DEFAULT_FOREGROUND = Color.blue;

        private final static Font DEFAULT_FONT = new Font("monospaced", Font.PLAIN,12);

        // LineNumber height (abends when I use MAX_VALUE)

        private final static int HEIGHT = Integer.MAX_VALUE - 1000000;

        // 设置左右页边空白

        private final static int MARGIN = 5;

        // Line height of this LineNumber component

        private int lineHeight;

        // Line height of this LineNumber component

        private int fontLineHeight;

        //当前行宽度

        private int currentRowWidth;

        // Metrics of this LineNumber component

        private FontMetrics fontMetrics;

        public LineNumber(JComponent component) {

                if (component == null) {

                        setBackground(DEFAULT_BACKGROUND);

                        setForeground(DEFAULT_FOREGROUND);

                        setFont(DEFAULT_FONT);

                } else {

                        setBackground(DEFAULT_BACKGROUND);

                        setForeground(component.getForeground());

                        setFont(component.getFont());

                }

                setPreferredSize(9999);

        }

        public void setPreferredSize(int row) {

                int width = fontMetrics.stringWidth(String.valueOf(row));

                if (currentRowWidth < width) {

                        currentRowWidth = width;

                        setPreferredSize(new Dimension(2 * MARGIN + width, HEIGHT));

                }

        }

        public void setFont(Font font) {

                super.setFont(font);

                fontMetrics = getFontMetrics(getFont());

                fontLineHeight = fontMetrics.getHeight();

        }

        public int getLineHeight() {

                if (lineHeight == 0)

                        return fontLineHeight;

                else

                        return lineHeight;

        }

        public void setLineHeight(int lineHeight) {

                if (lineHeight > 0)

                        this.lineHeight = lineHeight;

        }

       //起始偏移量

       public int getStartOffset() {

                return 4;

        }

        public void paintComponent(Graphics g) {

                int lineHeight = getLineHeight();

                int startOffset = getStartOffset();

                Rectangle drawHere = g.getClipBounds();

                // System.out.println( drawHere );

                // Paint the background

                g.setColor(getBackground());

                g.fillRect(drawHere.x, drawHere.y, drawHere.width, drawHere.height);

                // Determine the number of lines to draw in the foreground.

                g.setColor(getForeground());

                int startLineNumber = (drawHere.y / lineHeight) + 1;

                int endLineNumber = startLineNumber + (drawHere.height / lineHeight);

                int start = (drawHere.y / lineHeight) * lineHeight + lineHeight

                                - startOffset;

                // System.out.println( startLineNumber + " : " + endLineNumber + " : " +

                // start );

                for (int i = startLineNumber; i <= endLineNumber; i++) {

                        String lineNumber = String.valueOf(i);

                        int width = fontMetrics.stringWidth(lineNumber);

                        g.drawString(lineNumber, MARGIN + currentRowWidth - width, start);

                        start += lineHeight;

                }

                setPreferredSize(endLineNumber);

        }

        public static void main(String[] args) {

                JFrame frame = new JFrame("LineNumberDemo");

               // frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//关闭操作

                JPanel panel = new JPanel();

                frame.setContentPane(panel);

                panel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

                panel.setLayout(new BorderLayout());

                JTextArea textPane = new JTextArea();

                JScrollPane scrollPane = new JScrollPane(textPane);

                panel.add(scrollPane);

                scrollPane.setPreferredSize(new Dimension(300, 250));

//@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

                LineNumber lineNumber = new LineNumber(textPane);//look at here

                lineNumber.setPreferredSize(99999);

                scrollPane.setRowHeaderView(lineNumber);

//@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

                frame.pack();

                frame.setVisible(true);

        }

}