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;

        /**         * Convenience constructor for Text Components         */        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();        }

        /**         * The line height defaults to the line height of the font for this         * component. The line height can be overridden by setting it to a positive         * non-zero value.         */        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);        }}