The Point class encapsulates
x and y coordinates within a single object. It is probably one of the most
underused classes within Java. Although there are numerous places within
AWT where you would expect to see a Point,
its appearances are surprisingly rare. Java 1.1 is starting to
use Point more heavily. The
Point class is most often used
when a method needs to return a pair of coordinates; it lets the method
return both x and y as a single object. Unfortunately, Point
usually is not used when a method requires x and y coordinates as arguments;
for example, you would expect the Graphics
class to have a version of translate()
that takes a point as an argument, but there isn't one.
The Point class does not represent
a point on the screen. It is not a visual object; there is no drawPoint()
method.
Variables
The two public variables of Point
represent a pair of coordinates. They are accessible directly or use the
getLocation() method. There
is no predefined origin for the coordinate space.
- public int x
-
The coordinate that represents the horizontal position.
- public int y
-
The coordinate that represents the vertical position.
Constructors
- public Point ()
-
The first constructor creates an instance of Point
with an initial x value of 0 and an initial y value of 0.
- public Point (int x, int y)
-
The next constructor creates an instance of Point
with an initial x value of x
and an initial y value of y.
- public Point (Point p)
-
The last constructor creates an instance of Point
from another point, the x value of p.x
and an initial y value of p.y.
Locations
- public Point getLocation ()
-
The getLocation() method retrieves
the current location of this point as a new Point.
- public void setLocation (int x, int y)
public void move (int x, int y)
-
The setLocation() method changes
the point's location to (x,
y).
move() is the Java
1.0 name for this method.
- public void setLocation (Point p)
-
This setLocation() method changes
the point's location to (p.x,
p.y).
- public void translate (int x, int y)
-
The translate() method moves
the point's location
by adding the parameters (x,
y) to the corresponding fields
of the Point. If the original
Point p is (3, 4) and you call
p.translate(4, -5), the new
value of p is (7, -1).
Miscellaneous methods
- public int hashCode ()
-
The hashCode() method returns
a hash code for the point. The system calls this method when a Point
is used as the key for a hash table.
- public boolean equals (Object object)
-
The equals() method overrides
the Object.equals()
method to define equality for points. Two Point
objects are equal if their x and y values are equal.
- public String toString ()
-
The toString() method of Point
displays the current values of the x and y variables. For example:
java.awt.Point[x=100,y=200]
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