Package drawit

Class PointArrays

java.lang.Object

drawit.PointArrays

public class PointArrays
extends Object

Declares a number of methods useful for working with arrays of IntPoint objects.

Method Summary

Modifier and Type	Method	Description
static String	checkDefinesProperPolygon(IntPoint[] points)	Returns null if the given array of points defines a proper polygon; otherwise, returns a string describing why it does not.
static IntPoint[]	copy(IntPoint[] points)	Returns a new array with the same contents as the given array.
static IntPoint[]	insert(IntPoint[] points, int index, IntPoint point)	Returns a new array whose elements are the elements of the given array with the given point inserted at the given index.
static IntPoint[]	remove(IntPoint[] points, int index)	Returns a new array whose elements are the elements of the given array with the element at the given index removed.
static IntPoint[]	scale(IntPoint[] points, IntPoint origin, double xFactor, double yFactor)	Returns a new array whose elements are the elements of the given array, scaled by the given X and Y factors.
static IntPoint[]	translate(IntPoint[] points, IntVector delta)	Returns a new array whose elements are the elements of the given array, translated along the given vector.
static IntPoint[]	update(IntPoint[] points, int index, IntPoint value)	Returns a new array whose elements are the elements of the given array with the element at the given index replaced by the given point.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

checkDefinesProperPolygon

public static String checkDefinesProperPolygon(IntPoint[] points)

Returns null if the given array of points defines a proper polygon; otherwise, returns a string describing why it does not.

We interpret an array of N points as the polygon whose vertices are the given points and whose edges are the open line segments between point I and point (I + 1) % N, for I = 0, ..., N - 1.

A proper polygon is one where no two vertices coincide and no vertex is on any edge and no two edges intersect.

If there are exactly two points, the polygon is not proper. Notice that if there are more than two points and no two vertices coincide and no vertex is on any edge, then no two edges intersect at more than one point.

Preconditions:

points != null

Arrays.stream(points).allMatch(p -> p != null)

Inspects:

points

Mutates:

nothing

Postconditions:

(result == null) == (
    points.length != 2 &&
    IntStream.range(0, points.length).allMatch(i ->
        IntStream.range(0, points.length).allMatch(j -> i == j || !points[i].equals(points[j]))) &&
    IntStream.range(0, points.length).allMatch(i ->
        IntStream.range(0, points.length).allMatch(j -> !points[i].isOnLineSegment(points[j], points[(j + 1) % points.length]))) &&
    IntStream.range(0, points.length).allMatch(i ->
        IntStream.range(0, points.length).allMatch(j -> i == j ||
            !IntPoint.lineSegmentsIntersect(points[i], points[(i + 1) % points.length], points[j], points[(j + 1) % points.length])))
)

copy

public static IntPoint[] copy(IntPoint[] points)

Returns a new array with the same contents as the given array.

Preconditions:

points != null

Arrays.stream(points).allMatch(p -> p != null)

Inspects:

points

Mutates:

nothing

Creates:

result

Postconditions:

result != null

result.length == points.length

IntStream.range(0, points.length).allMatch(i -> result[i].equals(points[i]))

insert

public static IntPoint[] insert(IntPoint[] points, int index, IntPoint point)

Returns a new array whose elements are the elements of the given array with the given point inserted at the given index.

Preconditions:

points != null

Arrays.stream(points).allMatch(p -> p != null)

0 <= index && index <= points.length

point != null

Inspects:

points

Mutates:

nothing

Creates:

result

Postconditions:

result != null

result.length == points.length + 1

IntStream.range(0, index).allMatch(i -> result[i].equals(points[i]))

result[index].equals(point)

IntStream.range(index, points.length).allMatch(i -> result[i + 1].equals(points[i]))

remove

public static IntPoint[] remove(IntPoint[] points, int index)

Returns a new array whose elements are the elements of the given array with the element at the given index removed.

Preconditions:

points != null

Arrays.stream(points).allMatch(p -> p != null)

0 <= index && index < points.length

Inspects:

points

Mutates:

nothing

Creates:

result

Postconditions:

result != null

result.length == points.length - 1

IntStream.range(0, index).allMatch(i -> result[i].equals(points[i]))

IntStream.range(index + 1, points.length).allMatch(i -> result[i - 1].equals(points[i]))

update

public static IntPoint[] update(IntPoint[] points, int index, IntPoint value)

Returns a new array whose elements are the elements of the given array with the element at the given index replaced by the given point.

Preconditions:

points != null

0 <= index && index < points.length

value != null

Inspects:

points

Mutates:

nothing

Creates:

result

Postconditions:

result != null

result.length == points.length

IntStream.range(0, points.length).allMatch(i -> result[i].equals(i == index ? value : points[i]))

translate

public static IntPoint[] translate(IntPoint[] points, IntVector delta)

Returns a new array whose elements are the elements of the given array, translated along the given vector.

scale

public static IntPoint[] scale(IntPoint[] points, IntPoint origin, double xFactor, double yFactor)

Returns a new array whose elements are the elements of the given array, scaled by the given X and Y factors. The scaling is done with respect to the given origin. For example: scaling point (20, 20) with respect to origin (10, 10) by xFactor == 30 and yFactor == 50 results in point (310, 510).