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From: byhesed <byhesed@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Programming question determining two circle's relation
Date: Sat, 30 Apr 2011 09:01:42 -0700 (PDT)
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On 5=BF=F91=C0=CF, =BF=C0=C0=FC12=BD=C351=BA=D0, "Gavino" <inva...@invalid.=
invalid> wrote:
> "byhesed" <byhe...@gmail.com> wrote in message
>
> news:2bc6aa50-5730-4057-b016-3a2b7154f0e9@f15g2000pro.googlegroups.com...
>
>
>
>
>
>
>
>
>
> > Here is the correct answer.
>
> > public boolean contains(Circle2D circle) {
> > double distance =3D Math.pow(circle.x - getX(), 2.0) +
> > Math.pow(circle.y - getY(), 2.0);
> > if (distance <=3D (Math.pow(radius, 2.0) - Math.pow(circle.radius,
> > 2.0)))
> > return true;
> > else
> > return false;
>
> > }
>
> > public boolean overlaps(Circle2D circle) {
> > double distance =3D Math.pow(circle.x - getX(), 2.0) +
> > Math.pow(circle.y - getY(), 2.0);
> > if (distance < Math.abs(Math.pow(radius, 2.0) -
> > Math.pow(circle.radius, 2.0)))
> > return true;
>
> > else
> > return false;
> > }
>
> That's still wrong.
> 'contains' should have
> return Math.sqrt(distance) <=3D radius-circle.radius;
> and 'overlaps' should have
> return Math.sqrt(distance) <=3D radius+circle.radius;
> as can easily be seen by drawing a simple picture.
>
> Here I have retained your name 'distance' for what is actually the square=
 of
> the distance.

No, it's totally correct.

In the source code, distance means the distance between center of two
circles.
So, distance =3D Math.sqrt((x0-x1)^2 + (y0-y1)^2)

Here is conditions for determining positions of two circles.

Contains: d <=3D |r1 - r2|
Overlaps: |r1 - r2| < d < r1 + r2

Remember, circle is shown as x^2 + y^2 =3D r^2.