A
Constraints
object holds the
constraints that govern the way a component's size and position
change in a container controlled by a
SpringLayout
.
A
Constraints
object is
like a
Rectangle
, in that it
has
x
,
y
,
width
, and
height
properties.
In the
Constraints
object, however,
these properties have
Spring
values instead of integers.
In addition,
a
Constraints
object
can be manipulated as four edges
-- north, south, east, and west --
using the
constraint
property.
The following formulas are always true
for a Constraints
object (here WEST and x
are synonyms, as are and NORTH and y
):
EAST = WEST + WIDTH
SOUTH = NORTH + HEIGHT
HORIZONTAL_CENTER = WEST + WIDTH/2
VERTICAL_CENTER = NORTH + HEIGHT/2
ABSOLUTE_BASELINE = NORTH + RELATIVE_BASELINE*
For example, if you have specified the WIDTH and WEST (X) location
the EAST is calculated as WEST + WIDTH. If you instead specified
the WIDTH and EAST locations the WEST (X) location is then calculated
as EAST - WIDTH.
[RELATIVE_BASELINE is a private constraint that is set automatically when
the SpringLayout.Constraints(Component) constuctor is called or when
a constraints object is registered with a SpringLayout object.]
Note: In this document,
operators represent methods
in the Spring
class.
For example, "a + b" is equal to
Spring.sum(a, b)
,
and "a - b" is equal to
Spring.sum(a, Spring.minus(b))
.
See the
Spring
API documentation
for further details
of spring arithmetic.
Because a Constraints
object's properties --
representing its edges, size, and location -- can all be set
independently and yet are interrelated,
a Constraints
object can become over-constrained.
For example, if the WEST
, WIDTH
and
EAST
edges are all set, steps must be taken to ensure that
the first of the formulas above holds. To do this, the
Constraints
object throws away the least recently set
constraint so as to make the formulas hold.