随即函数求距离的疑惑，有很多不懂的，求解释

public class Point {
            int x,y;
            public Point(int x,int y){
                this.x=x;
                this.y=y;
                }
            public int distance(){
                return (int)Math.sqrt(x*x+y*y);
            }
            public static void main(String args[])
            {
                  Point p[]=new Point[9];
                  for(int i=0;i<p.length;i++)
                  {
                      p[i]=new Point((int)(Math.random()*10+1),(int)(Math.random()*10+1));//产生随机的点
                  }
                  Point temp = null;//排序        
                  for (int i = 0; i < 8; i++)
                  {            
                      for (int j = i + 1; j < 9; j++)
                      {               
                          if (p[i].distance() > p[j].distance())
                          {                    
                              temp = p[i];                    
                              p[i] = p[j];                    
                              p[j] = temp;               
                          }        
                      }
                  }
                  for (int i =0; i <9; i++)
                  {            
                      System.out.print(i+1+".产生的点("+p[i].x+","+p[i].y+") 到原点的距离是：");
                      System.out.println(p[i].distance());        
                  }
            }
            
}
老师处了个作业，在网上找到这个代码，但是有很多看不懂的，比如说this，还有p[i].distance() > p[j].distance()这一个是怎么调用前面的distance()方法的，distance()里面的x和y的值又是怎么和数组联系起来运算的。真心不懂了，大侠给点指示
----------------解决方案--------------------------------------------------------


public class Point {
            int x,y;
            public Point(int x,int y){//这是构造方法
                this.x=x;
                this.y=y;
                }
            public int distance(){//这是求解随即生成的点到原点的距离
                return (int)Math.sqrt(x*x+y*y);
            }
            public static void main(String args[])
            {
                  Point p[]=new Point[9];
                  for(int i=0;i<p.length;i++)
                  {
                      p[i]=new Point((int)(Math.random()*10+1),(int)(Math.random()*10+1));//产生随机的点
                  }
                  Point temp = null;//排序        
                  for (int i = 0; i < 8; i++)
                  {            
                      for (int j = i + 1; j < 9; j++)
                      {               
                          if (p[i].distance() > p[j].distance())
                          {                    
                              temp = p[i];                    
                              p[i] = p[j];                    
                              p[j] = temp;               
                          }        
                      }
                  }
                  for (int i =0; i <9; i++)
                  {            
                      System.out.print(i+1+".产生的点("+p[i].x+","+p[i].y+") 到原点的距离是：");//循环输出
                      System.out.println(p[i].distance()); // 此处循环一次，
                //那么p[i]就实例化了就是一个Point类的一个对象，那么就可以调用此类里的distance方法      
                  }
            }
            
}
不懂，再问    qq   1258601435
----------------解决方案--------------------------------------------------------