?//一條線段包含兩個端點? ?public?class?Point{????//點類 ???private?int?x,?y;?? ???public?Point(int?x,?int?y)?{? ???????this.x?=?x;? ???????this.y?=?y; ???} ???public?int?GetX()?{?? ???????return?x;? ???} ???public?int?GetY()?{?? ???????return?y;? ???} } class?Line{???//線段類 ???private?Point??p1,p2;?????//?兩端點 ???Line(Point?a,?Point?b)?{?? ??????p1?=?new?Point(a.GetX(),a.GetY());???//這里為什么不使用p1?=?a;?p2?=?b; ??????p2?=?new?Point(b.GetX(),b.GetY()); ???} ????public?double?Length()?{?? ??????return?Math.sqrt(Math.pow(p2.GetX()-p1.GetX(),2)?? ????????????????????????????????+?Math.pow(p2.GetY()-p1.GetY(),2)); ????} }在上面的代碼中：?p1?=?new?Point(a.GetX(),a.GetY());?? ?p2?=?new?Point(b.GetX(),b.GetY());?//這里為什么不使用p1?=?a;?p2?=?b;