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Copyright © 2006 Sun Microsystems, Inc. All rights reserved.

java.awt
Class Polygon

java.lang.Object
  java.awt.Polygon

All Implemented Interfaces:

Serializable, Shape

public class Polygon

extends Object

implements Shape, Serializable

The Polygon class encapsulates a description of a closed, two-dimensional region within a coordinate space. This region is bounded by an arbitrary number of line segments, each of which is one side of the polygon. Internally, a polygon comprises of a list of (x, y) coordinate pairs, where each pair defines a vertex of the polygon, and two successive pairs are the endpoints of a line that is a side of the polygon. The first and final pairs of (x, y) points are joined by a line segment that closes the polygon. This Polygon is defined with an even-odd winding rule. (The even-odd rule specifies that a point lies inside the path if a ray drawn in any direction from that point to infinity is crossed by path segments an odd number of times.) This class's hit-testing methods, which include the contains, intersects and inside methods, use the insideness definition described in the Shape class comments.

Since:

JDK1.0

See Also:

Shape, Serialized Form

Field Summary

protected Rectangle	bounds Bounds of the polygon.
int	npoints The total number of points.
int[]	xpoints The array of x coordinates.
int[]	ypoints The array of y coordinates.

Constructor Summary

Polygon()
Creates an empty polygon.

Polygon(int[] xpoints, int[] ypoints, int npoints)
Constructs and initializes a Polygon from the specified parameters.

Method Summary

void	addPoint(int x, int y) Appends the specified coordinates to this Polygon.
boolean	contains(int x, int y) Determines whether the specified coordinates are inside this Polygon.
boolean	contains(Point p) Determines whether the specified Point is inside this Polygon.
Rectangle	getBounds() Gets the bounding box of this Polygon.
void	invalidate() Invalidates or flushes any internally-cached data that depends on the vertex coordinates of this Polygon.
void	reset() Resets this Polygon object to an empty polygon.
void	translate(int deltaX, int deltaY) Translates the vertices of the Polygon by deltaX along the x axis and by deltaY along the y axis.

Methods inherited from class java.lang.Object

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

Field Detail

npoints

public int npoints

The total number of points. The value of npoints represents the number of valid points in this Polygon and might be less than the number of elements in xpoints or ypoints. This value can be NULL.

See Also:

addPoint(int, int)

xpoints

public int[] xpoints

The array of x coordinates. The number of elements in this array might be more than the number of x coordinates in this Polygon. The extra elements allow new points to be added to this Polygon without re-creating this array. The value of npoints is equal to the number of valid points in this Polygon.

See Also:

addPoint(int, int)

ypoints

public int[] ypoints

The array of y coordinates. The number of elements in this array might be more than the number of y coordinates in this Polygon. The extra elements allow new points to be added to this Polygon without re-creating this array. The value of npoints is equal to the number of valid points in this Polygon.

See Also:

addPoint(int, int)

bounds

protected Rectangle bounds

Bounds of the polygon. This value can be NULL. Please see the javadoc comments getBounds().

See Also:

getBounds()

Constructor Detail

Polygon

public Polygon()

Creates an empty polygon.

Polygon

public Polygon(int[] xpoints,
               int[] ypoints,
               int npoints)

Constructs and initializes a Polygon from the specified parameters.

Parameters:

xpoints - an array of x coordinates

ypoints - an array of y coordinates

npoints - the total number of points in the Polygon

Throws:

NegativeArraySizeException - if the value of npoints is negative.

IndexOutOfBoundsException - if npoints is greater than the length of xpoints or the length of ypoints.

NullPointerException - if xpoints or ypoints is null.

Method Detail

reset

public void reset()

Resets this Polygon object to an empty polygon. The coordinate arrays and the data in them are left untouched but the number of points is reset to zero to mark the old vertex data as invalid and to start accumulating new vertex data at the beginning. All internally-cached data relating to the old vertices are discarded. Note that since the coordinate arrays from before the reset are reused, creating a new empty Polygon might be more memory efficient than resetting the current one if the number of vertices in the new polygon data is significantly smaller than the number of vertices in the data from before the reset.

Since:

1.4

See Also:

invalidate()

invalidate

public void invalidate()

Invalidates or flushes any internally-cached data that depends on the vertex coordinates of this Polygon. This method should be called after any direct manipulation of the coordinates in the xpoints or ypoints arrays to avoid inconsistent results from methods such as getBounds or contains that might cache data from earlier computations relating to the vertex coordinates.

Since:

1.4

See Also:

getBounds()

translate

public void translate(int deltaX,
                      int deltaY)

Translates the vertices of the Polygon by deltaX along the x axis and by deltaY along the y axis.

Parameters:

deltaX - the amount to translate along the x axis

deltaY - the amount to translate along the y axis

Since:

JDK1.1

addPoint

public void addPoint(int x,
                     int y)

Appends the specified coordinates to this Polygon.

If an operation that calculates the bounding box of this Polygon has already been performed, such as getBounds or contains, then this method updates the bounding box.

Parameters:

x - the specified x coordinate

y - the specified y coordinate

See Also:

getBounds(), contains(java.awt.Point)

getBounds

public Rectangle getBounds()

Gets the bounding box of this Polygon. The bounding box is the smallest Rectangle whose sides are parallel to the x and y axes of the coordinate space, and can completely contain the Polygon.

Specified by:

getBounds in interface Shape

Returns:

a Rectangle that defines the bounds of this Polygon.

Since:

JDK1.1

contains

public boolean contains(Point p)

Determines whether the specified Point is inside this Polygon.

Parameters:

p - the specified Point to be tested

Returns:

true if the Polygon contains the Point; false otherwise.

contains

public boolean contains(int x,
                        int y)

Determines whether the specified coordinates are inside this Polygon.

Parameters:

x - the specified x coordinate to be tested

y - the specified y coordinate to be tested

Returns:

true if this Polygon contains the specified coordinates, (x, y); false otherwise.

Since:

JDK1.1