重载构造函数（相同运算结果，不同性能比较）

import java.awt.Point;
  class Box2  
    { int x1;
      int y1;
      int x2;
      int y2;
     
  Box2(int x,int y,int z,int w)
     { this.x1 = x;
       this.y1 = y;
       this.x2 = z;
       this.y2 = w;
      }
  Box2(Point topleft,Point bottomright) 
      { this(topleft.x,topleft.y,bottomright.x,bottomright.y); 
       }
  Box2(Point topleft,int wide,int height)
      { this(topleft.x,topleft.y,(topleft.x += wide),(topleft.y -= height)); 
       } 
 public static void main(String[] args)
       { Box2 box0 = new Box2(1,2,3,4);
         System.out.print(box0.x1+" "+box0.y1+" "+box0.x2+" "+box0.y2);
         Box2 box1 = new Box2(new Point(1,2),3,4);
         System.out.print(box1.x1+" "+box1.y1+" "+box1.x2+" "+box1.y2);
         Box2 box2 = new Box2(new Point(1,2),new Point(3,4));
         System.out.print(box2.x1+" "+box2.y1+" "+box2.x2+" "+box2.y2);
        }
      }  

import java.awt.Point;
class Box3 
  { int x1;
    int y1;
    int x2;
    int y2;
    
    Box3(int x,int y,int z,int w)
        { this.x1 = x;
          this.y1 = y;
          this.x2 = z;
          this.y2 = w;
         }
    Box3(Point lefttop,Point bottomright)
         { this.x1= lefttop.x;
           this.y1= lefttop.y;
           this.x2= bottomright.x;
           this.y2= bottomright.y;
          }
     Box3(Point lefttop,int width,int height)
          {this.x1 = lefttop.x;
           this.y1 = lefttop.y;
           this.x2 = lefttop.x + width;
           this.y2 = lefttop.y - height;
           }
      void printBox()
           { System.out.print(x1+" "+y1+" "+x2+" "+y2+" ");
            }
       public static void main (String[] args)
       { Box3 box3;
         box3 = new Box3(1,2,3,4);
         box3.printBox();
         box3 = new Box3(new Point(1,2),3,4);
         box3.printBox();
         box3 = new Box3(new Point(1,2),new Point(3,4));
         box3.printBox();
        }
     }

import java.awt.Point;
class Box4 
  { int x1;
    int y1;
    int x2;
    int y2;
    
    Box4(int x,int y,int z,int w)
        { this.x1 = x;
          this.y1 = y;
          this.x2 = z;
          this.y2 = w;
         }
    Box4(Point lefttop,Point bottomright)
         { this(lefttop.x,lefttop.y,bottomright.x,bottomright.y);
          }
     Box4(Point lefttop,int width,int height)
          {this(lefttop.x,lefttop.y,lefttop.x += width,lefttop.y -= height);
           }
      void printBox()
           { System.out.print(x1+" "+y1+" "+x2+" "+y2+" ");
            }
       public static void main (String[] args)
       { Box4 box4;
         box4 = new Box4(1,2,3,4);
         box4.printBox();
         box4 = new Box4(new Point(1,2),3,4);
         box4.printBox();
         box4 = new Box4(new Point(1,2),new Point(3,4));
         box4.printBox();
        }
     }