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}.
*
* @see SpringLayout
* @see SpringLayout.Constraints
*
* @author Philip Milne
* @since 1.4
*/
public abstract class Spring {
/**
* An integer value signifying that a property value has not yet been calculated.
*/
public static final int UNSET = Integer.MIN_VALUE;
/**
* Used by factory methods to create a Spring.
*
* @see #constant(int)
* @see #constant(int, int, int)
* @see #max
* @see #minus
* @see #sum
* @see SpringLayout.Constraints
*/
protected Spring() {}
/**
* Returns the minimum value of this Spring.
*
* @return the minimumValue property of this Spring
*/
public abstract int getMinimumValue();
/**
* Returns the preferred value of this Spring.
*
* @return the preferredValue of this Spring
*/
public abstract int getPreferredValue();
/**
* Returns the maximum value of this Spring.
*
* @return the maximumValue property of this Spring
*/
public abstract int getMaximumValue();
/**
* Returns the current value of this Spring.
*
* @return the value property of this Spring
*
* @see #setValue
*/
public abstract int getValue();
/**
* Sets the current value of this Spring to value.
*
* @param value the new setting of the value property
*
* @see #getValue
*/
public abstract void setValue(int value);
private double range(boolean contract) {
return contract ? (getPreferredValue() - getMinimumValue()) :
(getMaximumValue() - getPreferredValue());
}
/*pp*/ double getStrain() {
double delta = (getValue() - getPreferredValue());
return delta/range(getValue() < getPreferredValue());
}
/*pp*/ void setStrain(double strain) {
setValue(getPreferredValue() + (int)(strain * range(strain < 0)));
}
/*pp*/ boolean isCyclic(SpringLayout l) {
return false;
}
/*pp*/ static abstract class AbstractSpring extends Spring {
protected int size = UNSET;
public int getValue() {
return size != UNSET ? size : getPreferredValue();
}
public final void setValue(int size) {
if (this.size == size) {
return;
}
if (size == UNSET) {
clear();
} else {
setNonClearValue(size);
}
}
protected void clear() {
size = UNSET;
}
protected void setNonClearValue(int size) {
this.size = size;
}
}
private static class StaticSpring extends AbstractSpring {
protected int min;
protected int pref;
protected int max;
public StaticSpring(int pref) {
this(pref, pref, pref);
}
public StaticSpring(int min, int pref, int max) {
this.min = min;
this.pref = pref;
this.max = max;
}
public String toString() {
return "StaticSpring [" + min + ", " + pref + ", " + max + "]";
}
public int getMinimumValue() {
return min;
}
public int getPreferredValue() {
return pref;
}
public int getMaximumValue() {
return max;
}
}
private static class NegativeSpring extends Spring {
private Spring s;
public NegativeSpring(Spring s) {
this.s = s;
}
// Note the use of max value rather than minimum value here.
// See the opening preamble on arithmetic with springs.
public int getMinimumValue() {
return -s.getMaximumValue();
}
public int getPreferredValue() {
return -s.getPreferredValue();
}
public int getMaximumValue() {
return -s.getMinimumValue();
}
public int getValue() {
return -s.getValue();
}
public void setValue(int size) {
// No need to check for UNSET as
// Integer.MIN_VALUE == -Integer.MIN_VALUE.
s.setValue(-size);
}
/*pp*/ boolean isCyclic(SpringLayout l) {
return s.isCyclic(l);
}
}
private static class ScaleSpring extends Spring {
private Spring s;
private float factor;
private ScaleSpring(Spring s, float factor) {
this.s = s;
this.factor = factor;
}
public int getMinimumValue() {
return Math.round((factor < 0 ? s.getMaximumValue() : s.getMinimumValue()) * factor);
}
public int getPreferredValue() {
return Math.round(s.getPreferredValue() * factor);
}
public int getMaximumValue() {
return Math.round((factor < 0 ? s.getMinimumValue() : s.getMaximumValue()) * factor);
}
public int getValue() {
return Math.round(s.getValue() * factor);
}
public void setValue(int value) {
if (value == UNSET) {
s.setValue(UNSET);
} else {
s.setValue(Math.round(value / factor));
}
}
/*pp*/ boolean isCyclic(SpringLayout l) {
return s.isCyclic(l);
}
}
/*pp*/ static class WidthSpring extends AbstractSpring {
/*pp*/ Component c;
public WidthSpring(Component c) {
this.c = c;
}
public int getMinimumValue() {
return c.getMinimumSize().width;
}
public int getPreferredValue() {
return c.getPreferredSize().width;
}
public int getMaximumValue() {
// We will be doing arithmetic with the results of this call,
// so if a returned value is Integer.MAX_VALUE we will get
// arithmetic overflow. Truncate such values.
return Math.min(Short.MAX_VALUE, c.getMaximumSize().width);
}
}
/*pp*/ static class HeightSpring extends AbstractSpring {
/*pp*/ Component c;
public HeightSpring(Component c) {
this.c = c;
}
public int getMinimumValue() {
return c.getMinimumSize().height;
}
public int getPreferredValue() {
return c.getPreferredSize().height;
}
public int getMaximumValue() {
return Math.min(Short.MAX_VALUE, c.getMaximumSize().height);
}
}
/*pp*/ static abstract class SpringMap extends Spring {
private Spring s;
public SpringMap(Spring s) {
this.s = s;
}
protected abstract int map(int i);
protected abstract int inv(int i);
public int getMinimumValue() {
return map(s.getMinimumValue());
}
public int getPreferredValue() {
return map(s.getPreferredValue());
}
public int getMaximumValue() {
return Math.min(Short.MAX_VALUE, map(s.getMaximumValue()));
}
public int getValue() {
return map(s.getValue());
}
public void setValue(int value) {
if (value == UNSET) {
s.setValue(UNSET);
} else {
s.setValue(inv(value));
}
}
/*pp*/ boolean isCyclic(SpringLayout l) {
return s.isCyclic(l);
}
}
// Use the instance variables of the StaticSpring superclass to
// cache values that have already been calculated.
/*pp*/ static abstract class CompoundSpring extends StaticSpring {
protected Spring s1;
protected Spring s2;
public CompoundSpring(Spring s1, Spring s2) {
super(UNSET);
this.s1 = s1;
this.s2 = s2;
}
public String toString() {
return "CompoundSpring of " + s1 + " and " + s2;
}
protected void clear() {
super.clear();
min = pref = max = UNSET;
s1.setValue(UNSET);
s2.setValue(UNSET);
}
protected abstract int op(int x, int y);
public int getMinimumValue() {
if (min == UNSET) {
min = op(s1.getMinimumValue(), s2.getMinimumValue());
}
return min;
}
public int getPreferredValue() {
if (pref == UNSET) {
pref = op(s1.getPreferredValue(), s2.getPreferredValue());
}
return pref;
}
public int getMaximumValue() {
if (max == UNSET) {
max = op(s1.getMaximumValue(), s2.getMaximumValue());
}
return max;
}
public int getValue() {
if (size == UNSET) {
size = op(s1.getValue(), s2.getValue());
}
return size;
}
/*pp*/ boolean isCyclic(SpringLayout l) {
return l.isCyclic(s1) || l.isCyclic(s2);
}
};
private static class SumSpring extends CompoundSpring {
public SumSpring(Spring s1, Spring s2) {
super(s1, s2);
}
protected int op(int x, int y) {
return x + y;
}
protected void setNonClearValue(int size) {
super.setNonClearValue(size);
s1.setStrain(this.getStrain());
s2.setValue(size - s1.getValue());
}
}
private static class MaxSpring extends CompoundSpring {
public MaxSpring(Spring s1, Spring s2) {
super(s1, s2);
}
protected int op(int x, int y) {
return Math.max(x, y);
}
protected void setNonClearValue(int size) {
super.setNonClearValue(size);
s1.setValue(size);
s2.setValue(size);
}
}
/**
* Returns a strut -- a spring whose minimum, preferred, and
* maximum values each have the value pref.
*
* @param pref the minimum, preferred, and
* maximum values of the new spring
* @return a spring whose minimum, preferred, and
* maximum values each have the value pref
*
* @see Spring
*/
public static Spring constant(int pref) {
return constant(pref, pref, pref);
}
/**
* Returns a spring whose minimum, preferred, and
* maximum values have the values: min, pref,
* and max respectively.
*
* @param min the minimum value of the new spring
* @param pref the preferred value of the new spring
* @param max the maximum value of the new spring
* @return a spring whose minimum, preferred, and
* maximum values have the values: min, pref,
* and max respectively
*
* @see Spring
*/
public static Spring constant(int min, int pref, int max) {
return new StaticSpring(min, pref, max);
}
/**
* Returns -s: a spring running in the opposite direction to s.
*
* @return -s: a spring running in the opposite direction to s
*
* @see Spring
*/
public static Spring minus(Spring s) {
return new NegativeSpring(s);
}
/**
* 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 s1+s2: a spring representing s1 and s2 in series
*
* @see Spring
*/
public static Spring sum(Spring s1, Spring s2) {
return new SumSpring(s1, s2);
}
/**
* Returns max(s1, s2): a spring whose value is always greater than (or equal to)
* the values of both s1 and s2.
*
* @return max(s1, s2): a spring whose value is always greater than (or equal to)
* the values of both s1 and s2
* @see Spring
*/
public static Spring max(Spring s1, Spring s2) {
return new MaxSpring(s1, s2);
}
// Remove these, they're not used often and can be created using minus -
// as per these implementations.
/*pp*/ static Spring difference(Spring s1, Spring s2) {
return sum(s1, minus(s2));
}
/*
public static Spring min(Spring s1, Spring s2) {
return minus(max(minus(s1), minus(s2)));
}
*/
/**
* 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.
*
* @param s the spring to scale
* @param factor amount to scale by.
* @return a spring whose properties are those of the input spring s
* multiplied by factor
* @throws NullPointerException if s is null
* @since 1.5
*/
public static Spring scale(Spring s, float factor) {
checkArg(s);
return new ScaleSpring(s, factor);
}
/**
* 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.
*
* @param c Component used for calculating size
* @return a spring whose properties are defined by the horizontal component
* of the component's size methods.
* @throws NullPointerException if c is null
* @since 1.5
*/
public static Spring width(Component c) {
checkArg(c);
return new WidthSpring(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.
*
* @param c Component used for calculating size
* @return a spring whose properties are defined by the vertical component
* of the component's size methods.
* @throws NullPointerException if c is null
* @since 1.5
*/
public static Spring height(Component c) {
checkArg(c);
return new HeightSpring(c);
}
/**
* If s is null, this throws an NullPointerException.
*/
private static void checkArg(Object s) {
if (s == null) {
throw new NullPointerException("Argument must not be null");
}
}
}