JTextArea行号显示工具类

即针对TextArea进行行号显示

在使用时在对应JTextArea的jScrollPane上添加：

jScrollPane1.setRowHeaderView(new LineNumberHeaderView());

再创建一个插件类：

//package com.ui;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Rectangle;
//TEXTAREA 行号显示插件
public class LineNumberHeaderView extends javax.swing.JComponent {

    /**
	 * JAVA TextArea行数显示插件
	 */
	private static final long serialVersionUID = 1L;
	private final  Font DEFAULT_FONT = new Font(Font.MONOSPACED, Font.PLAIN, 11);
    public final Color DEFAULT_BACKGROUD = new Color(228, 228, 228);
    public final Color DEFAULT_FOREGROUD = Color.BLACK;
    public final int nHEIGHT = Integer.MAX_VALUE - 1000000;
    public final int MARGIN = 5;
    private int lineHeight;
    private int fontLineHeight;
    private int currentRowWidth;
    private FontMetrics fontMetrics;

    public LineNumberHeaderView() {
        setFont(DEFAULT_FONT);
        setForeground(DEFAULT_FOREGROUD);
        setBackground(DEFAULT_BACKGROUD);
        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 + 1, nHEIGHT));
        }
    }

    @Override
    public void setFont(Font font) {
        super.setFont(font);
        fontMetrics = getFontMetrics(getFont());
        fontLineHeight = fontMetrics.getHeight();
    }

    public int getLineHeight() {
        if (lineHeight == 0) {
            return fontLineHeight;
        }
        return lineHeight;
    }

    public void setLineHeight(int lineHeight) {
        if (lineHeight > 0) {
            this.lineHeight = lineHeight;
        }
    }

    public int getStartOffset() {
        return 4;
    }

    @Override
    protected void paintComponent(Graphics g) {
        int nlineHeight = getLineHeight();
        int startOffset = getStartOffset();
        Rectangle drawHere = g.getClipBounds();
        g.setColor(getBackground());
        g.fillRect(drawHere.x, drawHere.y, drawHere.width, drawHere.height);
        g.setColor(getForeground());
        int startLineNum = (drawHere.y / nlineHeight) + 1;
        int endLineNum = startLineNum + (drawHere.height / nlineHeight);
        int start = (drawHere.y / nlineHeight) * nlineHeight + nlineHeight - startOffset;
        for (int i = startLineNum; i <= endLineNum; ++i) {
            String lineNum = String.valueOf(i);
            int width = fontMetrics.stringWidth(lineNum);
            g.drawString(lineNum + " ", MARGIN + currentRowWidth - width - 1, start);
            start += nlineHeight;
        }
        setPreferredSize(endLineNum);
    }
}