学步园

示例代码如下：

public class LineNumberHeaderView extends javax.swing.JComponent {</p> <p> private final Font DEFAULT_FONT = new Font(Font.MONOSPACED, Font.PLAIN, 13);<br /> public final Color DEFAULT_BACKGROUD = new Color(228, 228, 228);<br /> public final Color DEFAULT_FOREGROUD = Color.red;<br /> public final int nHEIGHT = Integer.MAX_VALUE - 1000000;<br /> public final int MARGIN = 5;<br /> private int lineHeight;<br /> private int fontLineHeight;<br /> private int currentRowWidth;<br /> private FontMetrics fontMetrics;</p> <p> public LineNumberHeaderView() {<br /> setFont(DEFAULT_FONT);<br /> setForeground(DEFAULT_FOREGROUD);<br /> setBackground(DEFAULT_BACKGROUD);<br /> setPreferredSize(9999);<br /> }</p> <p> public void setPreferredSize(int row) {<br /> int width = fontMetrics.stringWidth(String.valueOf(row));<br /> if (currentRowWidth < width) {<br /> currentRowWidth = width;<br /> setPreferredSize(new Dimension(2 * MARGIN + width + 1, nHEIGHT));<br /> }<br /> }</p> <p> @Override<br /> public void setFont(Font font) {<br /> super.setFont(font);<br /> fontMetrics = getFontMetrics(getFont());<br /> fontLineHeight = fontMetrics.getHeight();<br /> }</p> <p> public int getLineHeight() {<br /> if (lineHeight == 0) {<br /> return fontLineHeight;<br /> }<br /> return lineHeight;<br /> }</p> <p> public void setLineHeight(int lineHeight) {<br /> if (lineHeight > 0) {<br /> this.lineHeight = lineHeight;<br /> }<br /> }</p> <p> public int getStartOffset() {<br /> return 4;<br /> }</p> <p> @Override<br /> protected void paintComponent(Graphics g) {<br /> int nlineHeight = getLineHeight();<br /> int startOffset = getStartOffset();<br /> Rectangle drawHere = g.getClipBounds();<br /> g.setColor(getBackground());<br /> g.fillRect(drawHere.x, drawHere.y, drawHere.width, drawHere.height);<br /> g.setColor(getForeground());<br /> int startLineNum = (drawHere.y / nlineHeight) + 1;<br /> int endLineNum = startLineNum + (drawHere.height / nlineHeight);<br /> int start = (drawHere.y / nlineHeight) * nlineHeight + nlineHeight - startOffset;<br /> for (int i = startLineNum; i <= endLineNum; ++i) {<br /> String lineNum = String.valueOf(i);<br /> int width = fontMetrics.stringWidth(lineNum);<br /> g.drawString(lineNum + " ", MARGIN + currentRowWidth - width - 1, start);<br /> start += nlineHeight;<br /> }<br /> setPreferredSize(endLineNum);<br /> }</p> <p> public static void main(String[] args){<br /> // try {<br /> // UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());<br /> // } catch (Exception e) {<br /> // e.printStackTrace();<br /> // }<br /> JFrame frame = new JFrame("带行号的TextArea Demo");<br /> JLabel label = new JLabel(" 编辑区域");<br /> LineNumberHeaderView view = new LineNumberHeaderView();<br /> JScrollPane scrollPane = new JScrollPane(new JTextArea());<br /> scrollPane.setRowHeaderView(view);<br /> frame.getContentPane().add(label, "North");<br /> frame.getContentPane().add(scrollPane,"Center");<br /> frame.setPreferredSize(new Dimension(300, 200));<br /> frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);<br /> frame.setBounds(200, 200, 300, 200);<br /> frame.setVisible(true);<br /> }<br /> }

运行效果如下所示：