15.5

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

public class Test_15 extends JFrame {
  public Test_15() {
    add(new PiramidPanel());
  }

  public static void main(String[] args) {
      Test_15 frame = new Test_15();
    frame.setSize(300, 400);
    frame.setTitle("Exercise15_5");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null); // Center the frame
    frame.setVisible(true);
  }
}

class PiramidPanel extends JPanel {
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    
    int x = 10, y =20;
    String s = "";
    for(int i=1 ; i < getHeight() ; i++){
        for(int j=0; j < i && j < getWidth(); j++){
            s = s + " " + (j+1);            
        }
        
        g.drawString(s, x, y);
        y += 20;
        s = "";
    }
    
  }
}

由于在PiramidPanel类中对于行和列的宽度使用了getWidth()和getHeight()函数做限制，所以在拖动窗口时，会根据窗口大小动态调整显示的行和列数。

效果图：