java.lang.Object javax.swing.Spring
Direct Known Subclasses:
HeightSpring, SumSpring, SpringMap, MaxSpring, SpringProxy, StaticSpring, NegativeSpring, CompoundSpring, ScaleSpring, AbstractSpring, WidthSpring
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 #sum method for details.
By defining simple arithmetic operations on Spring
s,
the behavior of a collection of Spring
s
can be reduced to that of an ordinary (noncompound) Spring
. We define
the "+", "", max, and min operators on
Spring
s 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 Spring
s as [a, b, c]
,
where a <= b <= c
, we can define the same
arithmetic operators on Spring
s:
[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 Spring
s 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 JavaBeans^{TM}
has been added to the java.beans
package.
Please see java.beans.XMLEncoder .
Philip
 Milne1.4
 Nested Class Summary:  

abstract static class  Spring.AbstractSpring  
static class  Spring.WidthSpring  
static class  Spring.HeightSpring  
abstract static class  Spring.SpringMap  
abstract static class  Spring.CompoundSpring 
Field Summary  

public static final int  UNSET  An integer value signifying that a property value has not yet been calculated. 
Constructor: 

protected Spring(){ } 
Method from javax.swing.Spring Summary: 

constant, constant, difference, getMaximumValue, getMinimumValue, getPreferredValue, getStrain, getValue, height, isCyclic, max, minus, scale, setStrain, setValue, sum, width 
Methods from java.lang.Object: 

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait 
Method from javax.swing.Spring Detail: 

public static Spring constant(int pref){ return constant(pref, pref, pref); }
pref . 
public static Spring constant(int min, int pref, int max){ return new StaticSpring(min, pref, max); }
min , pref ,
and max respectively. 
static Spring difference(Spring s1, Spring s2){ return sum(s1, minus(s2)); } 
abstract public int getMaximumValue()
Spring . 
abstract public int getMinimumValue()
Spring . 
abstract public int getPreferredValue()
Spring . 
double getStrain(){ double delta = (getValue()  getPreferredValue()); return delta/range(getValue() < getPreferredValue()); } 
abstract public int getValue()
Spring . 
public static Spring height(Component c){ checkArg(c); return new HeightSpring(c); }

boolean isCyclic(SpringLayout l){ return false; } 
public static Spring max(Spring s1, Spring s2){ return new MaxSpring(s1, s2); }
max(s1, s2) : a spring whose value is always greater than (or equal to)
the values of both s1 and s2 . 
public static Spring minus(Spring s){ return new NegativeSpring(s); }
s : a spring running in the opposite direction to s . 
public static Spring scale(Spring s, float factor){ checkArg(s); return new ScaleSpring(s, factor); }
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 midpoint' of its input  an operation that is useful for centering components in a container. 
void setStrain(double strain){ setValue(getPreferredValue() + (int)(strain * range(strain < 0))); } 
abstract public void setValue(int value)
Spring to value . 
public static Spring sum(Spring s1, Spring s2){ return new SumSpring(s1, s2); }
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  minand the strain of a spring in tension is: value  pref  max  prefWhen 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 . 
public static Spring width(Component c){ checkArg(c); return new WidthSpring(c); }
