histogram.java

java程序设计导论（daniel liang著） 所有偶数课后习题答案

// Histogram.java: Display a histogram in a panel to show the
// occurrence of the letters

import javax.swing.*;
import java.awt.*;

public class Histogram extends JPanel {
  // Count the occurrence of 26 letters
  private int count[];

  /**Set the count and display histogram*/
  public void showHistogram(int[] count) {
    this.count = count;
    repaint();
  }

  /**Paint the histogram*/
  public void paintComponent(Graphics g) {
    if (count == null) return; // No display if count is null

    super.paintComponent(g);

    // Find the panel size and bar width and interval dynamically
    int width = getSize().width;
    int height = getSize().height;
    int interval = (width-40)/count.length;
    int individualWidth = (int)(((width-40)/24)*0.60);

    // Find the maximum count. The maximum count has the highest bar
    int maxCount = 0;
    for (int i=0; i<count.length; i++) {
      if (maxCount < count[i])
        maxCount = count[i];
    }

    // x is the start position for the first bar in the histogram
    int x = 30;

    // Draw a horizontal base line
    g.drawLine(10, height-45, width-10, height-45);
    for (int i=0; i<count.length; i++) {
      // Find the bar height
      int barHeight =
        (int)(((double)count[i]/(double)maxCount)*(height-55));

      // Display a bar (i.e. rectangle)
      g.drawRect(x, height-45-barHeight, individualWidth,
        barHeight);

      // Display a letter under the base line
      g.drawString((char)(65+i)+"", x, height-30);

      // Move x for displaying the next character
      x += interval;
    }
  }

  /**Override getPreferredSize*/
  public Dimension getPreferredSize() {
    return new Dimension(300, 300);
  }
}