static class Point{

double x,y;

Point(double x, double y) {

this.x = x;

this.y = y;

}

@Override

public boolean equals(Object o) {

if (this == o) return true;

if (!(o instanceof Point)) return false;

Point point = (Point) o;

if (Double.compare(point.x, x) != 0) return false;

if (Double.compare(point.y, y) != 0) return false;

return true;

}

@Override

public int hashCode() {

int result;

long temp;

temp = Double.doubleToLongBits(x);

result = (int) (temp ^ (temp >>> 32));

temp = Double.doubleToLongBits(y);

result = 31 * result + (int) (temp ^ (temp >>> 32));

return result;

}

@Override

public String toString() {

return "{" +x +"," + y +'}';

}

}

static class Line{

Point a,b;

Line(Point a, Point b) {

this.a = a;

this.b = b;

}

@Override

public String toString() {

return "{" + a +"|" + b +'}';

}

@Override

public boolean equals(Object o) {

if (this == o) return true;

if (o == null || getClass() != o.getClass()) return false;

Line that = (Line) o;

return (this.a.equals(that.a) && this.b.equals(that.b) ||

this.a.equals(that.b) && this.b.equals(that.a));

}

@Override

public int hashCode() {

return (int) (a.x*a.y+b.x*b.y);

}

}

static List<Point> all = new ArrayList<Point>();

static{all.add(new Point(0,0));

all.add(new Point(0,2));

all.add(new Point(1,1));

all.add(new Point(1,-1));

all.add(new Point(2,2));

all.add(new Point(2,0));

all.add(new Point(2,1));

all.add(new Point(1,2));

all.add(new Point(1.1,2.7));

all.add(new Point(-1,-1));}

public static void main(String[] args) throws InterruptedException {

Map<Double,Set<Line>> m = new HashMap<Double,Set<Line>>();

for (int i = 0; i < all.size()-1; i++) {

Point a = all.get(i);

for (int j = i+1; j < all.size(); j++) {

Point b = all.get(j);

if (a.equals(b)) continue ;

Double slope = checkForNegativeExtremes( (a.y - b.y) / (a.x - b.x) );

Set<Line> l = m.get(slope);

if (l==null){

m.put(slope, l = new HashSet());

}

l.add(new Line(a, b));

}

}

for(Double slope : new ArrayList<Double>( m.keySet())){

Set<Line> lTmp = m.get(slope);

if (lTmp==null || lTmp.size()<=1) continue ;

Double slopePerpendicular = checkForNegativeExtremes(-1. / slope);

Set<Line> perpendiculars = m.remove(slopePerpendicular);

if (perpendiculars==null || perpendiculars.size()<=1) continue ;

List<Line> l = new ArrayList<Line>(lTmp);

for (int i = 0; i < l.size()-1; i++) {

Line l1 = l.get(i);

for (int j = i+1; j < l.size(); j++) {

Line l2 = l.get(j);

if (perpendiculars.contains(new Line(l1.a,l2.a)) && perpendiculars.contains(new Line(l1.b,l2.b))

// just in case we got them crossed here try the other way too.

|| perpendiculars.contains(new Line(l1.a,l2.b)) && perpendiculars.contains(new Line(l1.b,l2.a))){

System.out.println(l1.a+" "+l1.b+" "+l2.a+" "+l2.b+" form a square");

}

}

}

}

Thread.sleep(1000);

System.exit(0);

}

private static Double checkForNegativeExtremes(Double slope) {

if (slope.isInfinite() || slope.equals(-0.0)){

slope = Math.abs(slope); // this handles horizontal and perpendicular lines, dont want to differential between 0. and -0.

}

return slope;

}