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在本教程中

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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>低级别的绘制</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 2 页（共5 页）</nobr></font></td>
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<p>在创建 <code>Canvas</code> 时，我们需要继承 <code>Canvas</code> 类并至少覆盖其 <code>paint(Graphics g)</code> 方法。通过覆盖 <code>paint()</code> 方法，我们可以绘制股票图表：
         </p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
protected void paint(Graphics g) {
  // Clear background.
  g.setColor(255, 255, 255);
  g.fillRect(0, 0, screenH, screenV);

  // Draw Strings - Price, volume, etc.
  g.setColor(0, 0, 0);
  g.setFont(font);
  g.drawString("H: $"+UniStock.getString(sr.priceHigh) +
               ", L: $" + UniStock.getString(sr.priceLow),
               1, 1, Graphics.TOP | Graphics.LEFT);
  g.drawString("Volume: " + sr.volumn,
               1, fontH + 2, Graphics.TOP | Graphics.LEFT);

  // Draw the chart.

  for(int i=left+1; i&lt;=right;  i++) {
  // For each visible day (except the first day).

     StockRecord current = (StockRecord)sh.vec.elementAt(i);

     // Draw price chart.
     // Multiplication first, then division to increase accuracy.
     g.setColor(255, 51, 0);		 // Set color
     g.setStrokeStyle(Graphics.SOLID);
     g.drawLine(
           startX + (i-1-left)*step,
           startY + Y - (last.priceHigh-priceLowest)*Y/priceBase,
           startX + (i-left)*step,
           startY + Y - (current.priceHigh - priceLowest)*Y/priceBase
     );

    // Draw volume chart.

    last = current;


  } // End for loop.

}

         </code>
</pre>
<p>上述代码是我们的 <code>paint()</code> 方法。在该方法中，我们获得了对 <code>Graphics</code> 对象的引用；因此我们可以用它来执行实际的绘制工作。以下这些是 <code>Graphics</code> 中可用的主要绘制方法：
         </p>
<p>
          
<ul>
<li>
<code>drawArc(int x, int y, int width, int height, int
startAngle, int arcAngle)</code>
           
</li>
<li>
<code>drawChar(char character, int x, int y, int
anchor)</code>
           
</li>
<li>
<code>drawImage(Image img, int x, int y, int
anchor)</code>
           
</li>
<li>
<code>drawLine(int x1, int y1, int x2, int y2)</code>
           
</li>
<li>
<code>drawRect(int x, int y, int width, int
height)</code>
           
</li>
<li>
<code>drawString(String str, int x, int y, int
anchor)</code>
           
</li>
<li>
<code>fillArc(int x, int y, int width, int height, int
startAngle, int arcAngle)</code>
           
</li>
<li>
<code>fillRect(int x, int y, int width, int
height)</code>
           
</li>
<li>
<code>fillRoundRect(int x, int y, int width, int height,
int arcWidth, int arcHeight)</code>
           
</li>
</ul>
         
</p>
<p>在 UniStock 中，我们使用 <code>drawString()</code> 来绘制选定交易日的价格和成交量。然后通过连接 <code>drawLine()</code> 为每个时期创建的小片段来绘制价格和成交量图表。
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