新手学了半天，做到99乘法表不会了，求帮忙

import javax.swing.JOptionPane;

public class Nine
{
    static String str="";
    public static void draw(int i,int j)
    {
        if(j<=i)
        {
            str+=i+"*"+j+"="+(i*j);
            str+=i*j>9?" ":"   ";
            draw(i,j+1);  
        }
    }
    public static void draw(int n)         
    {                                            
        if(n>0)                                 
        {                                      
            draw(n-1);                       
            draw(n,1);                           
            str+="\n";                        
        }                                      
    }                                          
    public Nine()
    {
        draw(9);
        JOptionPane.showMessageDialog(null, "打印结果:\n"+str,"九九乘法表",JOptionPane.INFORMATION_MESSAGE);
        str="";
    }
    public static void main(String[] args)
    {
        new Nine();
    }   
}