Springpublic abstract class Spring extends Object An instance of the Spring class holds three properties that
characterize its behavior: the minimum, preferred, and
maximum values. Each of these properties may be involved in
defining its fourth, value, property based on a series of rules.
An instance of the Spring class can be visualized as a
mechanical spring that provides a corrective force as the spring is compressed
or stretched away from its preferred value. This force is modelled
as linear function of the distance from the preferred value, but with
two different constants -- one for the compressional force and one for the
tensional one. Those constants are specified by the minimum and maximum
values of the spring such that a spring at its minimum value produces an
equal and opposite force to that which is created when it is at its
maximum value. The difference between the preferred and
minimum values, therefore, represents the ease with which the
spring can be compressed and the difference between its maximum
and preferred values, indicates the ease with which the
Spring can be extended.
See the {@link #sum} method for details.
By defining simple arithmetic operations on Springs,
the behavior of a collection of Springs
can be reduced to that of an ordinary (non-compound) Spring. We define
the "+", "-", max, and min operators on
Springs so that, in each case, the result is a Spring
whose characteristics bear a useful mathematical relationship to its constituent
springs.
A Spring can be treated as a pair of intervals
with a single common point: the preferred value.
The following rules define some of the
arithmetic operators that can be applied to intervals
([a, b] refers to the interval
from a
to b,
where a <= b).
[a1, b1] + [a2, b2] = [a1 + a2, b1 + b2]
-[a, b] = [-b, -a]
max([a1, b1], [a2, b2]) = [max(a1, a2), max(b1, b2)]
If we denote Springs as [a, b, c],
where a <= b <= c, we can define the same
arithmetic operators on Springs:
[a1, b1, c1] + [a2, b2, c2] = [a1 + a2, b1 + b2, c1 + c2]
-[a, b, c] = [-c, -b, -a]
max([a1, b1, c1], [a2, b2, c2]) = [max(a1, a2), max(b1, b2), max(c1, c2)]
With both intervals and Springs we can define "-" and min
in terms of negation:
X - Y = X + (-Y)
min(X, Y) = -max(-X, -Y)
For the static methods in this class that embody the arithmetic
operators, we do not actually perform the operation in question as
that would snapshot the values of the properties of the method's arguments
at the time the static method is called. Instead, the static methods
create a new Spring instance containing references to
the method's arguments so that the characteristics of the new spring track the
potentially changing characteristics of the springs from which it
was made. This is a little like the idea of a lazy value
in a functional language.
If you are implementing a SpringLayout you
can find further information and examples in
How to Use SpringLayout,
a section in The Java Tutorial.
Warning:
Serialized objects of this class will not be compatible with
future Swing releases. The current serialization support is
appropriate for short term storage or RMI between applications running
the same version of Swing. As of 1.4, support for long term storage
of all JavaBeansTM
has been added to the java.beans package.
Please see {@link java.beans.XMLEncoder}. |
| Fields Summary |
|---|
| public static final int | UNSETAn integer value signifying that a property value has not yet been calculated. |
| Constructors Summary |
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protected Spring()Used by factory methods to create a Spring.
|
| Methods Summary |
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| private static void | checkArg(java.lang.Object s)If s is null, this throws an NullPointerException.
if (s == null) {
throw new NullPointerException("Argument must not be null");
}
| | public static javax.swing.Spring | constant(int pref)Returns a strut -- a spring whose minimum, preferred, and
maximum values each have the value pref.
return constant(pref, pref, pref);
| | public static javax.swing.Spring | constant(int min, int pref, int max)Returns a spring whose minimum, preferred, and
maximum values have the values: min, pref,
and max respectively.
return new StaticSpring(min, pref, max);
| | static javax.swing.Spring | difference(javax.swing.Spring s1, javax.swing.Spring s2)
return sum(s1, minus(s2));
| | public abstract int | getMaximumValue()Returns the maximum value of this Spring.
| | public abstract int | getMinimumValue()Returns the minimum value of this Spring.
| | public abstract int | getPreferredValue()Returns the preferred value of this Spring.
| | double | getStrain()
double delta = (getValue() - getPreferredValue());
return delta/range(getValue() < getPreferredValue());
| | public abstract int | getValue()Returns the current value of this Spring.
| | public static javax.swing.Spring | height(java.awt.Component c)Returns a spring whose minimum, preferred, maximum
and value properties are defined by the heights of the minimumSize,
preferredSize, maximumSize and size properties
of the supplied component. The returned spring is a 'wrapper' implementation
whose methods call the appropriate size methods of the supplied component.
The minimum, preferred, maximum and value properties of the returned spring
therefore report the current state of the appropriate properties in the
component and track them as they change.
checkArg(c);
return new HeightSpring(c);
| | boolean | isCyclic(javax.swing.SpringLayout l)
return false;
| | public static javax.swing.Spring | max(javax.swing.Spring s1, javax.swing.Spring s2)Returns max(s1, s2): a spring whose value is always greater than (or equal to)
the values of both s1 and s2.
return new MaxSpring(s1, s2);
| | public static javax.swing.Spring | minus(javax.swing.Spring s)Returns -s: a spring running in the opposite direction to s.
return new NegativeSpring(s);
| | private double | range(boolean contract)
return contract ? (getPreferredValue() - getMinimumValue()) :
(getMaximumValue() - getPreferredValue());
| | public static javax.swing.Spring | scale(javax.swing.Spring s, float factor)Returns a spring whose minimum, preferred, maximum
and value properties are each multiples of the properties of the
argument spring, s. Minimum and maximum properties are
swapped when factor is negative (in accordance with the
rules of interval arithmetic).
When factor is, for example, 0.5f the result represents 'the mid-point'
of its input - an operation that is useful for centering components in
a container.
checkArg(s);
return new ScaleSpring(s, factor);
| | void | setStrain(double strain)
setValue(getPreferredValue() + (int)(strain * range(strain < 0)));
| | public abstract void | setValue(int value)Sets the current value of this Spring to value.
| | public static javax.swing.Spring | sum(javax.swing.Spring s1, javax.swing.Spring s2)Returns s1+s2: a spring representing s1 and s2
in series. In a sum, s3, of two springs, s1 and s2,
the strains of s1, s2, and s3 are maintained
at the same level (to within the precision implied by their integer values).
The strain of a spring in compression is:
value - pref
------------
pref - min
and the strain of a spring in tension is:
value - pref
------------
max - pref
When setValue is called on the sum spring, s3, the strain
in s3 is calculated using one of the formulas above. Once the strain of
the sum is known, the values of s1 and s2 are
then set so that they are have a strain equal to that of the sum. The formulas are
evaluated so as to take rounding errors into account and ensure that the sum of
the values of s1 and s2 is exactly equal to
the value of s3.
return new SumSpring(s1, s2);
| | public static javax.swing.Spring | width(java.awt.Component c)Returns a spring whose minimum, preferred, maximum
and value properties are defined by the widths of the minimumSize,
preferredSize, maximumSize and size properties
of the supplied component. The returned spring is a 'wrapper' implementation
whose methods call the appropriate size methods of the supplied component.
The minimum, preferred, maximum and value properties of the returned spring
therefore report the current state of the appropriate properties in the
component and track them as they change.
checkArg(c);
return new WidthSpring(c);
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