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src/java.desktop/share/classes/javax/swing/Spring.java

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  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package javax.swing;
  26 
  27 import java.awt.Component;
  28 
  29 /**
  30  *  An instance of the <code>Spring</code> class holds three properties that
  31  *  characterize its behavior: the <em>minimum</em>, <em>preferred</em>, and
  32  *  <em>maximum</em> values. Each of these properties may be involved in
  33  *  defining its fourth, <em>value</em>, property based on a series of rules.
  34  *  <p>
  35  *  An instance of the <code>Spring</code> class can be visualized as a
  36  *  mechanical spring that provides a corrective force as the spring is compressed
  37  *  or stretched away from its preferred value. This force is modelled
  38  *  as linear function of the distance from the preferred value, but with
  39  *  two different constants -- one for the compressional force and one for the
  40  *  tensional one. Those constants are specified by the minimum and maximum
  41  *  values of the spring such that a spring at its minimum value produces an
  42  *  equal and opposite force to that which is created when it is at its
  43  *  maximum value. The difference between the <em>preferred</em> and
  44  *  <em>minimum</em> values, therefore, represents the ease with which the
  45  *  spring can be compressed and the difference between its <em>maximum</em>
  46  *  and <em>preferred</em> values, indicates the ease with which the
  47  *  <code>Spring</code> can be extended.
  48  *  See the {@link #sum} method for details.
  49  *
  50  *  <p>
  51  *  By defining simple arithmetic operations on <code>Spring</code>s,
  52  *  the behavior of a collection of <code>Spring</code>s
  53  *  can be reduced to that of an ordinary (non-compound) <code>Spring</code>. We define
  54  *  the "+", "-", <em>max</em>, and <em>min</em> operators on
  55  *  <code>Spring</code>s so that, in each case, the result is a <code>Spring</code>
  56  *  whose characteristics bear a useful mathematical relationship to its constituent
  57  *  springs.
  58  *
  59  *  <p>
  60  *  A <code>Spring</code> can be treated as a pair of intervals
  61  *  with a single common point: the preferred value.
  62  *  The following rules define some of the
  63  *  arithmetic operators that can be applied to intervals
  64  *  (<code>[a, b]</code> refers to the interval
  65  *  from <code>a</code>
  66  *  to <code>b</code>,
  67  *  where <code>a &lt;= b</code>).
  68  *
  69  *  <pre>
  70  *          [a1, b1] + [a2, b2] = [a1 + a2, b1 + b2]
  71  *
  72  *                      -[a, b] = [-b, -a]
  73  *
  74  *      max([a1, b1], [a2, b2]) = [max(a1, a2), max(b1, b2)]
  75  *  </pre>
  76  *  <p>
  77  *
  78  *  If we denote <code>Spring</code>s as <code>[a, b, c]</code>,
  79  *  where <code>a &lt;= b &lt;= c</code>, we can define the same
  80  *  arithmetic operators on <code>Spring</code>s:
  81  *
  82  *  <pre>
  83  *          [a1, b1, c1] + [a2, b2, c2] = [a1 + a2, b1 + b2, c1 + c2]
  84  *
  85  *                           -[a, b, c] = [-c, -b, -a]
  86  *
  87  *      max([a1, b1, c1], [a2, b2, c2]) = [max(a1, a2), max(b1, b2), max(c1, c2)]
  88  *  </pre>
  89  *  <p>
  90  *  With both intervals and <code>Spring</code>s we can define "-" and <em>min</em>
  91  *  in terms of negation:
  92  *
  93  *  <pre>
  94  *      X - Y = X + (-Y)
  95  *
  96  *      min(X, Y) = -max(-X, -Y)
  97  *  </pre>
  98  *  <p>
  99  *  For the static methods in this class that embody the arithmetic
 100  *  operators, we do not actually perform the operation in question as
 101  *  that would snapshot the values of the properties of the method's arguments
 102  *  at the time the static method is called. Instead, the static methods
 103  *  create a new <code>Spring</code> instance containing references to
 104  *  the method's arguments so that the characteristics of the new spring track the
 105  *  potentially changing characteristics of the springs from which it
 106  *  was made. This is a little like the idea of a <em>lazy value</em>
 107  *  in a functional language.
 108  * <p>
 109  * If you are implementing a <code>SpringLayout</code> you
 110  * can find further information and examples in
 111  * <a
 112  href="http://docs.oracle.com/javase/tutorial/uiswing/layout/spring.html">How to Use SpringLayout</a>,
 113  * a section in <em>The Java Tutorial.</em>
 114  * <p>
 115  * <strong>Warning:</strong>
 116  * Serialized objects of this class will not be compatible with
 117  * future Swing releases. The current serialization support is
 118  * appropriate for short term storage or RMI between applications running
 119  * the same version of Swing.  As of 1.4, support for long term storage
 120  * of all JavaBeans&trade;
 121  * has been added to the <code>java.beans</code> package.
 122  * Please see {@link java.beans.XMLEncoder}.
 123  *
 124  * @see SpringLayout
 125  * @see SpringLayout.Constraints
 126  *
 127  * @author      Philip Milne
 128  * @since       1.4
 129  */
 130 @SuppressWarnings("serial") // Same-version serialization only
 131 public abstract class Spring {
 132 
 133     /**
 134      * An integer value signifying that a property value has not yet been calculated.
 135      */
 136     public static final int UNSET = Integer.MIN_VALUE;
 137 
 138     /**
 139      * Used by factory methods to create a <code>Spring</code>.
 140      *
 141      * @see #constant(int)
 142      * @see #constant(int, int, int)
 143      * @see #max
 144      * @see #minus
 145      * @see #sum
 146      * @see SpringLayout.Constraints
 147      */
 148     protected Spring() {}
 149 
 150     /**
 151      * Returns the <em>minimum</em> value of this <code>Spring</code>.
 152      *
 153      * @return the <code>minimumValue</code> property of this <code>Spring</code>
 154      */
 155     public abstract int getMinimumValue();
 156 
 157     /**
 158      * Returns the <em>preferred</em> value of this <code>Spring</code>.
 159      *
 160      * @return the <code>preferredValue</code> of this <code>Spring</code>
 161      */
 162     public abstract int getPreferredValue();
 163 
 164     /**
 165      * Returns the <em>maximum</em> value of this <code>Spring</code>.
 166      *
 167      * @return the <code>maximumValue</code> property of this <code>Spring</code>
 168      */
 169     public abstract int getMaximumValue();
 170 
 171     /**
 172      * Returns the current <em>value</em> of this <code>Spring</code>.
 173      *
 174      * @return  the <code>value</code> property of this <code>Spring</code>
 175      *
 176      * @see #setValue
 177      */
 178     public abstract int getValue();
 179 
 180     /**
 181      * Sets the current <em>value</em> of this <code>Spring</code> to <code>value</code>.
 182      *
 183      * @param   value the new setting of the <code>value</code> property
 184      *
 185      * @see #getValue
 186      */
 187     public abstract void setValue(int value);
 188 
 189     private double range(boolean contract) {
 190         return contract ? (getPreferredValue() - getMinimumValue()) :
 191                           (getMaximumValue() - getPreferredValue());
 192     }
 193 
 194     /*pp*/ double getStrain() {
 195         double delta = (getValue() - getPreferredValue());
 196         return delta/range(getValue() < getPreferredValue());
 197     }
 198 
 199     /*pp*/ void setStrain(double strain) {
 200         setValue(getPreferredValue() + (int)(strain * range(strain < 0)));
 201     }
 202 
 203     /*pp*/ boolean isCyclic(SpringLayout l) {


 497 
 498     private static class MaxSpring extends CompoundSpring {
 499 
 500         public MaxSpring(Spring s1, Spring s2) {
 501             super(s1, s2);
 502         }
 503 
 504         protected int op(int x, int y) {
 505             return Math.max(x, y);
 506         }
 507 
 508         protected void setNonClearValue(int size) {
 509             super.setNonClearValue(size);
 510             s1.setValue(size);
 511             s2.setValue(size);
 512         }
 513     }
 514 
 515     /**
 516      * Returns a strut -- a spring whose <em>minimum</em>, <em>preferred</em>, and
 517      * <em>maximum</em> values each have the value <code>pref</code>.
 518      *
 519      * @param  pref the <em>minimum</em>, <em>preferred</em>, and
 520      *         <em>maximum</em> values of the new spring
 521      * @return a spring whose <em>minimum</em>, <em>preferred</em>, and
 522      *         <em>maximum</em> values each have the value <code>pref</code>
 523      *
 524      * @see Spring
 525      */
 526      public static Spring constant(int pref) {
 527          return constant(pref, pref, pref);
 528      }
 529 
 530     /**
 531      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, and
 532      * <em>maximum</em> values have the values: <code>min</code>, <code>pref</code>,
 533      * and <code>max</code> respectively.
 534      *
 535      * @param  min the <em>minimum</em> value of the new spring
 536      * @param  pref the <em>preferred</em> value of the new spring
 537      * @param  max the <em>maximum</em> value of the new spring
 538      * @return a spring whose <em>minimum</em>, <em>preferred</em>, and
 539      *         <em>maximum</em> values have the values: <code>min</code>, <code>pref</code>,
 540      *         and <code>max</code> respectively
 541      *
 542      * @see Spring
 543      */
 544      public static Spring constant(int min, int pref, int max) {
 545          return new StaticSpring(min, pref, max);
 546      }
 547 
 548 
 549     /**
 550      * Returns {@code -s}: a spring running in the opposite direction to {@code s}.
 551      *
 552      * @param s a {@code Spring} object
 553      * @return {@code -s}: a spring running in the opposite direction to {@code s}
 554      *
 555      * @see Spring
 556      */
 557     public static Spring minus(Spring s) {
 558         return new NegativeSpring(s);
 559     }
 560 
 561     /**
 562      * Returns <code>s1+s2</code>: a spring representing <code>s1</code> and <code>s2</code>
 563      * in series. In a sum, <code>s3</code>, of two springs, <code>s1</code> and <code>s2</code>,
 564      * the <em>strains</em> of <code>s1</code>, <code>s2</code>, and <code>s3</code> are maintained
 565      * at the same level (to within the precision implied by their integer <em>value</em>s).
 566      * The strain of a spring in compression is:
 567      * <pre>
 568      *         value - pref
 569      *         ------------
 570      *          pref - min
 571      * </pre>
 572      * and the strain of a spring in tension is:
 573      * <pre>
 574      *         value - pref
 575      *         ------------
 576      *          max - pref
 577      * </pre>
 578      * When <code>setValue</code> is called on the sum spring, <code>s3</code>, the strain
 579      * in <code>s3</code> is calculated using one of the formulas above. Once the strain of
 580      * the sum is known, the <em>value</em>s of <code>s1</code> and <code>s2</code> are
 581      * then set so that they are have a strain equal to that of the sum. The formulas are
 582      * evaluated so as to take rounding errors into account and ensure that the sum of
 583      * the <em>value</em>s of <code>s1</code> and <code>s2</code> is exactly equal to
 584      * the <em>value</em> of <code>s3</code>.
 585      *
 586      * @param s1 a {@code Spring} object
 587      * @param s2 a {@code Spring} object
 588      * @return <code>s1+s2</code>: a spring representing <code>s1</code> and <code>s2</code> in series
 589      *
 590      * @see Spring
 591      */
 592      public static Spring sum(Spring s1, Spring s2) {
 593          return new SumSpring(s1, s2);
 594      }
 595 
 596     /**
 597      * Returns {@code max(s1, s2)}: a spring whose value is always greater than (or equal to)
 598      *         the values of both {@code s1} and {@code s2}.
 599      *
 600      * @param s1 a {@code Spring} object
 601      * @param s2 a {@code Spring} object
 602      * @return {@code max(s1, s2)}: a spring whose value is always greater than (or equal to)
 603      *         the values of both {@code s1} and {@code s2}
 604      * @see Spring
 605      */
 606     public static Spring max(Spring s1, Spring s2) {
 607         return new MaxSpring(s1, s2);
 608     }
 609 
 610     // Remove these, they're not used often and can be created using minus -
 611     // as per these implementations.
 612 
 613     /*pp*/ static Spring difference(Spring s1, Spring s2) {
 614         return sum(s1, minus(s2));
 615     }
 616 
 617     /*
 618     public static Spring min(Spring s1, Spring s2) {
 619         return minus(max(minus(s1), minus(s2)));
 620     }
 621     */
 622 
 623     /**
 624      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 625      * and <em>value</em> properties are each multiples of the properties of the
 626      * argument spring, <code>s</code>. Minimum and maximum properties are
 627      * swapped when <code>factor</code> is negative (in accordance with the
 628      * rules of interval arithmetic).
 629      * <p>
 630      * When factor is, for example, 0.5f the result represents 'the mid-point'
 631      * of its input - an operation that is useful for centering components in
 632      * a container.
 633      *
 634      * @param s the spring to scale
 635      * @param factor amount to scale by.
 636      * @return  a spring whose properties are those of the input spring <code>s</code>
 637      * multiplied by <code>factor</code>
 638      * @throws NullPointerException if <code>s</code> is null
 639      * @since 1.5
 640      */
 641     public static Spring scale(Spring s, float factor) {
 642         checkArg(s);
 643         return new ScaleSpring(s, factor);
 644     }
 645 
 646     /**
 647      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 648      * and <em>value</em> properties are defined by the widths of the <em>minimumSize</em>,
 649      * <em>preferredSize</em>, <em>maximumSize</em> and <em>size</em> properties
 650      * of the supplied component. The returned spring is a 'wrapper' implementation
 651      * whose methods call the appropriate size methods of the supplied component.
 652      * The minimum, preferred, maximum and value properties of the returned spring
 653      * therefore report the current state of the appropriate properties in the
 654      * component and track them as they change.
 655      *
 656      * @param c Component used for calculating size
 657      * @return  a spring whose properties are defined by the horizontal component
 658      * of the component's size methods.
 659      * @throws NullPointerException if <code>c</code> is null
 660      * @since 1.5
 661      */
 662     public static Spring width(Component c) {
 663         checkArg(c);
 664         return new WidthSpring(c);
 665     }
 666 
 667     /**
 668      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 669      * and <em>value</em> properties are defined by the heights of the <em>minimumSize</em>,
 670      * <em>preferredSize</em>, <em>maximumSize</em> and <em>size</em> properties
 671      * of the supplied component. The returned spring is a 'wrapper' implementation
 672      * whose methods call the appropriate size methods of the supplied component.
 673      * The minimum, preferred, maximum and value properties of the returned spring
 674      * therefore report the current state of the appropriate properties in the
 675      * component and track them as they change.
 676      *
 677      * @param c Component used for calculating size
 678      * @return  a spring whose properties are defined by the vertical component
 679      * of the component's size methods.
 680      * @throws NullPointerException if <code>c</code> is null
 681      * @since 1.5
 682      */
 683     public static Spring height(Component c) {
 684         checkArg(c);
 685         return new HeightSpring(c);
 686     }
 687 
 688 
 689     /**
 690      * If <code>s</code> is null, this throws an NullPointerException.
 691      */
 692     private static void checkArg(Object s) {
 693         if (s == null) {
 694             throw new NullPointerException("Argument must not be null");
 695         }
 696     }
 697 }


  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package javax.swing;
  26 
  27 import java.awt.Component;
  28 
  29 /**
  30  *  An instance of the {@code Spring} class holds three properties that
  31  *  characterize its behavior: the <em>minimum</em>, <em>preferred</em>, and
  32  *  <em>maximum</em> values. Each of these properties may be involved in
  33  *  defining its fourth, <em>value</em>, property based on a series of rules.
  34  *  <p>
  35  *  An instance of the {@code Spring} class can be visualized as a
  36  *  mechanical spring that provides a corrective force as the spring is compressed
  37  *  or stretched away from its preferred value. This force is modelled
  38  *  as linear function of the distance from the preferred value, but with
  39  *  two different constants -- one for the compressional force and one for the
  40  *  tensional one. Those constants are specified by the minimum and maximum
  41  *  values of the spring such that a spring at its minimum value produces an
  42  *  equal and opposite force to that which is created when it is at its
  43  *  maximum value. The difference between the <em>preferred</em> and
  44  *  <em>minimum</em> values, therefore, represents the ease with which the
  45  *  spring can be compressed and the difference between its <em>maximum</em>
  46  *  and <em>preferred</em> values, indicates the ease with which the
  47  *  {@code Spring} can be extended.
  48  *  See the {@link #sum} method for details.
  49  *
  50  *  <p>
  51  *  By defining simple arithmetic operations on {@code Spring}s,
  52  *  the behavior of a collection of {@code Spring}s
  53  *  can be reduced to that of an ordinary (non-compound) {@code Spring}. We define
  54  *  the "+", "-", <em>max</em>, and <em>min</em> operators on
  55  *  {@code Spring}s so that, in each case, the result is a {@code Spring}
  56  *  whose characteristics bear a useful mathematical relationship to its constituent
  57  *  springs.
  58  *
  59  *  <p>
  60  *  A {@code Spring} can be treated as a pair of intervals
  61  *  with a single common point: the preferred value.
  62  *  The following rules define some of the
  63  *  arithmetic operators that can be applied to intervals
  64  *  ({@code [a, b]} refers to the interval
  65  *  from {@code a}
  66  *  to {@code b},
  67  *  where {@code a <= b}).
  68  *
  69  *  <pre>
  70  *          [a1, b1] + [a2, b2] = [a1 + a2, b1 + b2]
  71  *
  72  *                      -[a, b] = [-b, -a]
  73  *
  74  *      max([a1, b1], [a2, b2]) = [max(a1, a2), max(b1, b2)]
  75  *  </pre>
  76  *  <p>
  77  *
  78  *  If we denote {@code Spring}s as {@code [a, b, c]},
  79  *  where {@code a <= b <= c}, we can define the same
  80  *  arithmetic operators on {@code Spring}s:
  81  *
  82  *  <pre>
  83  *          [a1, b1, c1] + [a2, b2, c2] = [a1 + a2, b1 + b2, c1 + c2]
  84  *
  85  *                           -[a, b, c] = [-c, -b, -a]
  86  *
  87  *      max([a1, b1, c1], [a2, b2, c2]) = [max(a1, a2), max(b1, b2), max(c1, c2)]
  88  *  </pre>
  89  *  <p>
  90  *  With both intervals and {@code Spring}s we can define "-" and <em>min</em>
  91  *  in terms of negation:
  92  *
  93  *  <pre>
  94  *      X - Y = X + (-Y)
  95  *
  96  *      min(X, Y) = -max(-X, -Y)
  97  *  </pre>
  98  *  <p>
  99  *  For the static methods in this class that embody the arithmetic
 100  *  operators, we do not actually perform the operation in question as
 101  *  that would snapshot the values of the properties of the method's arguments
 102  *  at the time the static method is called. Instead, the static methods
 103  *  create a new {@code Spring} instance containing references to
 104  *  the method's arguments so that the characteristics of the new spring track the
 105  *  potentially changing characteristics of the springs from which it
 106  *  was made. This is a little like the idea of a <em>lazy value</em>
 107  *  in a functional language.
 108  * <p>
 109  * If you are implementing a {@code SpringLayout} you
 110  * can find further information and examples in
 111  * <a
 112  href="http://docs.oracle.com/javase/tutorial/uiswing/layout/spring.html">How to Use SpringLayout</a>,
 113  * a section in <em>The Java Tutorial.</em>
 114  * <p>
 115  * <strong>Warning:</strong>
 116  * Serialized objects of this class will not be compatible with
 117  * future Swing releases. The current serialization support is
 118  * appropriate for short term storage or RMI between applications running
 119  * the same version of Swing.  As of 1.4, support for long term storage
 120  * of all JavaBeans&trade;
 121  * has been added to the {@code java.beans} package.
 122  * Please see {@link java.beans.XMLEncoder}.
 123  *
 124  * @see SpringLayout
 125  * @see SpringLayout.Constraints
 126  *
 127  * @author      Philip Milne
 128  * @since       1.4
 129  */
 130 @SuppressWarnings("serial") // Same-version serialization only
 131 public abstract class Spring {
 132 
 133     /**
 134      * An integer value signifying that a property value has not yet been calculated.
 135      */
 136     public static final int UNSET = Integer.MIN_VALUE;
 137 
 138     /**
 139      * Used by factory methods to create a {@code Spring}.
 140      *
 141      * @see #constant(int)
 142      * @see #constant(int, int, int)
 143      * @see #max
 144      * @see #minus
 145      * @see #sum
 146      * @see SpringLayout.Constraints
 147      */
 148     protected Spring() {}
 149 
 150     /**
 151      * Returns the <em>minimum</em> value of this {@code Spring}.
 152      *
 153      * @return the {@code minimumValue} property of this {@code Spring}
 154      */
 155     public abstract int getMinimumValue();
 156 
 157     /**
 158      * Returns the <em>preferred</em> value of this {@code Spring}.
 159      *
 160      * @return the {@code preferredValue} of this {@code Spring}
 161      */
 162     public abstract int getPreferredValue();
 163 
 164     /**
 165      * Returns the <em>maximum</em> value of this {@code Spring}.
 166      *
 167      * @return the {@code maximumValue} property of this {@code Spring}
 168      */
 169     public abstract int getMaximumValue();
 170 
 171     /**
 172      * Returns the current <em>value</em> of this {@code Spring}.
 173      *
 174      * @return  the {@code value} property of this {@code Spring}
 175      *
 176      * @see #setValue
 177      */
 178     public abstract int getValue();
 179 
 180     /**
 181      * Sets the current <em>value</em> of this {@code Spring} to {@code value}.
 182      *
 183      * @param   value the new setting of the {@code value} property
 184      *
 185      * @see #getValue
 186      */
 187     public abstract void setValue(int value);
 188 
 189     private double range(boolean contract) {
 190         return contract ? (getPreferredValue() - getMinimumValue()) :
 191                           (getMaximumValue() - getPreferredValue());
 192     }
 193 
 194     /*pp*/ double getStrain() {
 195         double delta = (getValue() - getPreferredValue());
 196         return delta/range(getValue() < getPreferredValue());
 197     }
 198 
 199     /*pp*/ void setStrain(double strain) {
 200         setValue(getPreferredValue() + (int)(strain * range(strain < 0)));
 201     }
 202 
 203     /*pp*/ boolean isCyclic(SpringLayout l) {


 497 
 498     private static class MaxSpring extends CompoundSpring {
 499 
 500         public MaxSpring(Spring s1, Spring s2) {
 501             super(s1, s2);
 502         }
 503 
 504         protected int op(int x, int y) {
 505             return Math.max(x, y);
 506         }
 507 
 508         protected void setNonClearValue(int size) {
 509             super.setNonClearValue(size);
 510             s1.setValue(size);
 511             s2.setValue(size);
 512         }
 513     }
 514 
 515     /**
 516      * Returns a strut -- a spring whose <em>minimum</em>, <em>preferred</em>, and
 517      * <em>maximum</em> values each have the value {@code pref}.
 518      *
 519      * @param  pref the <em>minimum</em>, <em>preferred</em>, and
 520      *         <em>maximum</em> values of the new spring
 521      * @return a spring whose <em>minimum</em>, <em>preferred</em>, and
 522      *         <em>maximum</em> values each have the value {@code pref}
 523      *
 524      * @see Spring
 525      */
 526      public static Spring constant(int pref) {
 527          return constant(pref, pref, pref);
 528      }
 529 
 530     /**
 531      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, and
 532      * <em>maximum</em> values have the values: {@code min}, {@code pref},
 533      * and {@code max} respectively.
 534      *
 535      * @param  min the <em>minimum</em> value of the new spring
 536      * @param  pref the <em>preferred</em> value of the new spring
 537      * @param  max the <em>maximum</em> value of the new spring
 538      * @return a spring whose <em>minimum</em>, <em>preferred</em>, and
 539      *         <em>maximum</em> values have the values: {@code min}, {@code pref},
 540      *         and {@code max} respectively
 541      *
 542      * @see Spring
 543      */
 544      public static Spring constant(int min, int pref, int max) {
 545          return new StaticSpring(min, pref, max);
 546      }
 547 
 548 
 549     /**
 550      * Returns {@code -s}: a spring running in the opposite direction to {@code s}.
 551      *
 552      * @param s a {@code Spring} object
 553      * @return {@code -s}: a spring running in the opposite direction to {@code s}
 554      *
 555      * @see Spring
 556      */
 557     public static Spring minus(Spring s) {
 558         return new NegativeSpring(s);
 559     }
 560 
 561     /**
 562      * Returns {@code s1+s2}: a spring representing {@code s1} and {@code s2}
 563      * in series. In a sum, {@code s3}, of two springs, {@code s1} and {@code s2},
 564      * the <em>strains</em> of {@code s1}, {@code s2}, and {@code s3} are maintained
 565      * at the same level (to within the precision implied by their integer <em>value</em>s).
 566      * The strain of a spring in compression is:
 567      * <pre>
 568      *         value - pref
 569      *         ------------
 570      *          pref - min
 571      * </pre>
 572      * and the strain of a spring in tension is:
 573      * <pre>
 574      *         value - pref
 575      *         ------------
 576      *          max - pref
 577      * </pre>
 578      * When {@code setValue} is called on the sum spring, {@code s3}, the strain
 579      * in {@code s3} is calculated using one of the formulas above. Once the strain of
 580      * the sum is known, the <em>value</em>s of {@code s1} and {@code s2} are
 581      * then set so that they are have a strain equal to that of the sum. The formulas are
 582      * evaluated so as to take rounding errors into account and ensure that the sum of
 583      * the <em>value</em>s of {@code s1} and {@code s2} is exactly equal to
 584      * the <em>value</em> of {@code s3}.
 585      *
 586      * @param s1 a {@code Spring} object
 587      * @param s2 a {@code Spring} object
 588      * @return {@code s1+s2}: a spring representing {@code s1} and {@code s2} in series
 589      *
 590      * @see Spring
 591      */
 592      public static Spring sum(Spring s1, Spring s2) {
 593          return new SumSpring(s1, s2);
 594      }
 595 
 596     /**
 597      * Returns {@code max(s1, s2)}: a spring whose value is always greater than (or equal to)
 598      *         the values of both {@code s1} and {@code s2}.
 599      *
 600      * @param s1 a {@code Spring} object
 601      * @param s2 a {@code Spring} object
 602      * @return {@code max(s1, s2)}: a spring whose value is always greater than (or equal to)
 603      *         the values of both {@code s1} and {@code s2}
 604      * @see Spring
 605      */
 606     public static Spring max(Spring s1, Spring s2) {
 607         return new MaxSpring(s1, s2);
 608     }
 609 
 610     // Remove these, they're not used often and can be created using minus -
 611     // as per these implementations.
 612 
 613     /*pp*/ static Spring difference(Spring s1, Spring s2) {
 614         return sum(s1, minus(s2));
 615     }
 616 
 617     /*
 618     public static Spring min(Spring s1, Spring s2) {
 619         return minus(max(minus(s1), minus(s2)));
 620     }
 621     */
 622 
 623     /**
 624      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 625      * and <em>value</em> properties are each multiples of the properties of the
 626      * argument spring, {@code s}. Minimum and maximum properties are
 627      * swapped when {@code factor} is negative (in accordance with the
 628      * rules of interval arithmetic).
 629      * <p>
 630      * When factor is, for example, 0.5f the result represents 'the mid-point'
 631      * of its input - an operation that is useful for centering components in
 632      * a container.
 633      *
 634      * @param s the spring to scale
 635      * @param factor amount to scale by.
 636      * @return  a spring whose properties are those of the input spring {@code s}
 637      * multiplied by {@code factor}
 638      * @throws NullPointerException if {@code s} is null
 639      * @since 1.5
 640      */
 641     public static Spring scale(Spring s, float factor) {
 642         checkArg(s);
 643         return new ScaleSpring(s, factor);
 644     }
 645 
 646     /**
 647      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 648      * and <em>value</em> properties are defined by the widths of the <em>minimumSize</em>,
 649      * <em>preferredSize</em>, <em>maximumSize</em> and <em>size</em> properties
 650      * of the supplied component. The returned spring is a 'wrapper' implementation
 651      * whose methods call the appropriate size methods of the supplied component.
 652      * The minimum, preferred, maximum and value properties of the returned spring
 653      * therefore report the current state of the appropriate properties in the
 654      * component and track them as they change.
 655      *
 656      * @param c Component used for calculating size
 657      * @return  a spring whose properties are defined by the horizontal component
 658      * of the component's size methods.
 659      * @throws NullPointerException if {@code c} is null
 660      * @since 1.5
 661      */
 662     public static Spring width(Component c) {
 663         checkArg(c);
 664         return new WidthSpring(c);
 665     }
 666 
 667     /**
 668      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 669      * and <em>value</em> properties are defined by the heights of the <em>minimumSize</em>,
 670      * <em>preferredSize</em>, <em>maximumSize</em> and <em>size</em> properties
 671      * of the supplied component. The returned spring is a 'wrapper' implementation
 672      * whose methods call the appropriate size methods of the supplied component.
 673      * The minimum, preferred, maximum and value properties of the returned spring
 674      * therefore report the current state of the appropriate properties in the
 675      * component and track them as they change.
 676      *
 677      * @param c Component used for calculating size
 678      * @return  a spring whose properties are defined by the vertical component
 679      * of the component's size methods.
 680      * @throws NullPointerException if {@code c} is null
 681      * @since 1.5
 682      */
 683     public static Spring height(Component c) {
 684         checkArg(c);
 685         return new HeightSpring(c);
 686     }
 687 
 688 
 689     /**
 690      * If {@code s} is null, this throws an NullPointerException.
 691      */
 692     private static void checkArg(Object s) {
 693         if (s == null) {
 694             throw new NullPointerException("Argument must not be null");
 695         }
 696     }
 697 }
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