1 /*
   2  * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  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="https://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 public abstract class Spring {
 131 
 132     /**
 133      * An integer value signifying that a property value has not yet been calculated.
 134      */
 135     public static final int UNSET = Integer.MIN_VALUE;
 136 
 137     /**
 138      * Used by factory methods to create a <code>Spring</code>.
 139      *
 140      * @see #constant(int)
 141      * @see #constant(int, int, int)
 142      * @see #max
 143      * @see #minus
 144      * @see #sum
 145      * @see SpringLayout.Constraints
 146      */
 147     protected Spring() {}
 148 
 149     /**
 150      * Returns the <em>minimum</em> value of this <code>Spring</code>.
 151      *
 152      * @return the <code>minimumValue</code> property of this <code>Spring</code>
 153      */
 154     public abstract int getMinimumValue();
 155 
 156     /**
 157      * Returns the <em>preferred</em> value of this <code>Spring</code>.
 158      *
 159      * @return the <code>preferredValue</code> of this <code>Spring</code>
 160      */
 161     public abstract int getPreferredValue();
 162 
 163     /**
 164      * Returns the <em>maximum</em> value of this <code>Spring</code>.
 165      *
 166      * @return the <code>maximumValue</code> property of this <code>Spring</code>
 167      */
 168     public abstract int getMaximumValue();
 169 
 170     /**
 171      * Returns the current <em>value</em> of this <code>Spring</code>.
 172      *
 173      * @return  the <code>value</code> property of this <code>Spring</code>
 174      *
 175      * @see #setValue
 176      */
 177     public abstract int getValue();
 178 
 179     /**
 180      * Sets the current <em>value</em> of this <code>Spring</code> to <code>value</code>.
 181      *
 182      * @param   value the new setting of the <code>value</code> property
 183      *
 184      * @see #getValue
 185      */
 186     public abstract void setValue(int value);
 187 
 188     private double range(boolean contract) {
 189         return contract ? (getPreferredValue() - getMinimumValue()) :
 190                           (getMaximumValue() - getPreferredValue());
 191     }
 192 
 193     /*pp*/ double getStrain() {
 194         double delta = (getValue() - getPreferredValue());
 195         return delta/range(getValue() < getPreferredValue());
 196     }
 197 
 198     /*pp*/ void setStrain(double strain) {
 199         setValue(getPreferredValue() + (int)(strain * range(strain < 0)));
 200     }
 201 
 202     /*pp*/ boolean isCyclic(SpringLayout l) {
 203         return false;
 204     }
 205 
 206     /*pp*/ static abstract class AbstractSpring extends Spring {
 207         protected int size = UNSET;
 208 
 209         public int getValue() {
 210             return size != UNSET ? size : getPreferredValue();
 211         }
 212 
 213         public final void setValue(int size) {
 214             if (this.size == size) {
 215                 return;
 216             }
 217             if (size == UNSET) {
 218                 clear();
 219             } else {
 220                 setNonClearValue(size);
 221             }
 222         }
 223 
 224         protected void clear() {
 225             size = UNSET;
 226         }
 227 
 228         protected void setNonClearValue(int size) {
 229             this.size = size;
 230         }
 231     }
 232 
 233     private static class StaticSpring extends AbstractSpring {
 234         protected int min;
 235         protected int pref;
 236         protected int max;
 237 
 238         public StaticSpring(int pref) {
 239             this(pref, pref, pref);
 240         }
 241 
 242         public StaticSpring(int min, int pref, int max) {
 243             this.min = min;
 244             this.pref = pref;
 245             this.max = max;
 246         }
 247 
 248          public String toString() {
 249              return "StaticSpring [" + min + ", " + pref + ", " + max + "]";
 250          }
 251 
 252          public int getMinimumValue() {
 253             return min;
 254         }
 255 
 256         public int getPreferredValue() {
 257             return pref;
 258         }
 259 
 260         public int getMaximumValue() {
 261             return max;
 262         }
 263     }
 264 
 265     private static class NegativeSpring extends Spring {
 266         private Spring s;
 267 
 268         public NegativeSpring(Spring s) {
 269             this.s = s;
 270         }
 271 
 272 // Note the use of max value rather than minimum value here.
 273 // See the opening preamble on arithmetic with springs.
 274 
 275         public int getMinimumValue() {
 276             return -s.getMaximumValue();
 277         }
 278 
 279         public int getPreferredValue() {
 280             return -s.getPreferredValue();
 281         }
 282 
 283         public int getMaximumValue() {
 284             return -s.getMinimumValue();
 285         }
 286 
 287         public int getValue() {
 288             return -s.getValue();
 289         }
 290 
 291         public void setValue(int size) {
 292             // No need to check for UNSET as
 293             // Integer.MIN_VALUE == -Integer.MIN_VALUE.
 294             s.setValue(-size);
 295         }
 296 
 297         /*pp*/ boolean isCyclic(SpringLayout l) {
 298             return s.isCyclic(l);
 299         }
 300     }
 301 
 302     private static class ScaleSpring extends Spring {
 303         private Spring s;
 304         private float factor;
 305 
 306         private ScaleSpring(Spring s, float factor) {
 307             this.s = s;
 308             this.factor = factor;
 309         }
 310 
 311         public int getMinimumValue() {
 312             return Math.round((factor < 0 ? s.getMaximumValue() : s.getMinimumValue()) * factor);
 313         }
 314 
 315         public int getPreferredValue() {
 316             return Math.round(s.getPreferredValue() * factor);
 317         }
 318 
 319         public int getMaximumValue() {
 320             return Math.round((factor < 0 ? s.getMinimumValue() : s.getMaximumValue()) * factor);
 321         }
 322 
 323         public int getValue() {
 324             return Math.round(s.getValue() * factor);
 325         }
 326 
 327         public void setValue(int value) {
 328             if (value == UNSET) {
 329                 s.setValue(UNSET);
 330             } else {
 331                 s.setValue(Math.round(value / factor));
 332             }
 333         }
 334 
 335         /*pp*/ boolean isCyclic(SpringLayout l) {
 336             return s.isCyclic(l);
 337         }
 338     }
 339 
 340     /*pp*/ static class WidthSpring extends AbstractSpring {
 341         /*pp*/ Component c;
 342 
 343         public WidthSpring(Component c) {
 344             this.c = c;
 345         }
 346 
 347         public int getMinimumValue() {
 348             return c.getMinimumSize().width;
 349         }
 350 
 351         public int getPreferredValue() {
 352             return c.getPreferredSize().width;
 353         }
 354 
 355         public int getMaximumValue() {
 356             // We will be doing arithmetic with the results of this call,
 357             // so if a returned value is Integer.MAX_VALUE we will get
 358             // arithmetic overflow. Truncate such values.
 359             return Math.min(Short.MAX_VALUE, c.getMaximumSize().width);
 360         }
 361     }
 362 
 363      /*pp*/  static class HeightSpring extends AbstractSpring {
 364         /*pp*/ Component c;
 365 
 366         public HeightSpring(Component c) {
 367             this.c = c;
 368         }
 369 
 370         public int getMinimumValue() {
 371             return c.getMinimumSize().height;
 372         }
 373 
 374         public int getPreferredValue() {
 375             return c.getPreferredSize().height;
 376         }
 377 
 378         public int getMaximumValue() {
 379             return Math.min(Short.MAX_VALUE, c.getMaximumSize().height);
 380         }
 381     }
 382 
 383    /*pp*/ static abstract class SpringMap extends Spring {
 384        private Spring s;
 385 
 386        public SpringMap(Spring s) {
 387            this.s = s;
 388        }
 389 
 390        protected abstract int map(int i);
 391 
 392        protected abstract int inv(int i);
 393 
 394        public int getMinimumValue() {
 395            return map(s.getMinimumValue());
 396        }
 397 
 398        public int getPreferredValue() {
 399            return map(s.getPreferredValue());
 400        }
 401 
 402        public int getMaximumValue() {
 403            return Math.min(Short.MAX_VALUE, map(s.getMaximumValue()));
 404        }
 405 
 406        public int getValue() {
 407            return map(s.getValue());
 408        }
 409 
 410        public void setValue(int value) {
 411            if (value == UNSET) {
 412                s.setValue(UNSET);
 413            } else {
 414                s.setValue(inv(value));
 415            }
 416        }
 417 
 418        /*pp*/ boolean isCyclic(SpringLayout l) {
 419            return s.isCyclic(l);
 420        }
 421    }
 422 
 423 // Use the instance variables of the StaticSpring superclass to
 424 // cache values that have already been calculated.
 425     /*pp*/ static abstract class CompoundSpring extends StaticSpring {
 426         protected Spring s1;
 427         protected Spring s2;
 428 
 429         public CompoundSpring(Spring s1, Spring s2) {
 430             super(UNSET);
 431             this.s1 = s1;
 432             this.s2 = s2;
 433         }
 434 
 435         public String toString() {
 436             return "CompoundSpring of " + s1 + " and " + s2;
 437         }
 438 
 439         protected void clear() {
 440             super.clear();
 441             min = pref = max = UNSET;
 442             s1.setValue(UNSET);
 443             s2.setValue(UNSET);
 444         }
 445 
 446         protected abstract int op(int x, int y);
 447 
 448         public int getMinimumValue() {
 449             if (min == UNSET) {
 450                 min = op(s1.getMinimumValue(), s2.getMinimumValue());
 451             }
 452             return min;
 453         }
 454 
 455         public int getPreferredValue() {
 456             if (pref == UNSET) {
 457                 pref = op(s1.getPreferredValue(), s2.getPreferredValue());
 458             }
 459             return pref;
 460         }
 461 
 462         public int getMaximumValue() {
 463             if (max == UNSET) {
 464                 max = op(s1.getMaximumValue(), s2.getMaximumValue());
 465             }
 466             return max;
 467         }
 468 
 469         public int getValue() {
 470             if (size == UNSET) {
 471                 size = op(s1.getValue(), s2.getValue());
 472             }
 473             return size;
 474         }
 475 
 476         /*pp*/ boolean isCyclic(SpringLayout l) {
 477             return l.isCyclic(s1) || l.isCyclic(s2);
 478         }
 479     };
 480 
 481      private static class SumSpring extends CompoundSpring {
 482          public SumSpring(Spring s1, Spring s2) {
 483              super(s1, s2);
 484          }
 485 
 486          protected int op(int x, int y) {
 487              return x + y;
 488          }
 489 
 490          protected void setNonClearValue(int size) {
 491              super.setNonClearValue(size);
 492              s1.setStrain(this.getStrain());
 493              s2.setValue(size - s1.getValue());
 494          }
 495      }
 496 
 497     private static class MaxSpring extends CompoundSpring {
 498 
 499         public MaxSpring(Spring s1, Spring s2) {
 500             super(s1, s2);
 501         }
 502 
 503         protected int op(int x, int y) {
 504             return Math.max(x, y);
 505         }
 506 
 507         protected void setNonClearValue(int size) {
 508             super.setNonClearValue(size);
 509             s1.setValue(size);
 510             s2.setValue(size);
 511         }
 512     }
 513 
 514     /**
 515      * Returns a strut -- a spring whose <em>minimum</em>, <em>preferred</em>, and
 516      * <em>maximum</em> values each have the value <code>pref</code>.
 517      *
 518      * @param  pref the <em>minimum</em>, <em>preferred</em>, and
 519      *         <em>maximum</em> values of the new spring
 520      * @return a spring whose <em>minimum</em>, <em>preferred</em>, and
 521      *         <em>maximum</em> values each have the value <code>pref</code>
 522      *
 523      * @see Spring
 524      */
 525      public static Spring constant(int pref) {
 526          return constant(pref, pref, pref);
 527      }
 528 
 529     /**
 530      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, and
 531      * <em>maximum</em> values have the values: <code>min</code>, <code>pref</code>,
 532      * and <code>max</code> respectively.
 533      *
 534      * @param  min the <em>minimum</em> value of the new spring
 535      * @param  pref the <em>preferred</em> value of the new spring
 536      * @param  max the <em>maximum</em> value of the new spring
 537      * @return a spring whose <em>minimum</em>, <em>preferred</em>, and
 538      *         <em>maximum</em> values have the values: <code>min</code>, <code>pref</code>,
 539      *         and <code>max</code> respectively
 540      *
 541      * @see Spring
 542      */
 543      public static Spring constant(int min, int pref, int max) {
 544          return new StaticSpring(min, pref, max);
 545      }
 546 
 547 
 548     /**
 549      * Returns <code>-s</code>: a spring running in the opposite direction to <code>s</code>.
 550      *
 551      * @return <code>-s</code>: a spring running in the opposite direction to <code>s</code>
 552      *
 553      * @see Spring
 554      */
 555     public static Spring minus(Spring s) {
 556         return new NegativeSpring(s);
 557     }
 558 
 559     /**
 560      * Returns <code>s1+s2</code>: a spring representing <code>s1</code> and <code>s2</code>
 561      * in series. In a sum, <code>s3</code>, of two springs, <code>s1</code> and <code>s2</code>,
 562      * the <em>strains</em> of <code>s1</code>, <code>s2</code>, and <code>s3</code> are maintained
 563      * at the same level (to within the precision implied by their integer <em>value</em>s).
 564      * The strain of a spring in compression is:
 565      * <pre>
 566      *         value - pref
 567      *         ------------
 568      *          pref - min
 569      * </pre>
 570      * and the strain of a spring in tension is:
 571      * <pre>
 572      *         value - pref
 573      *         ------------
 574      *          max - pref
 575      * </pre>
 576      * When <code>setValue</code> is called on the sum spring, <code>s3</code>, the strain
 577      * in <code>s3</code> is calculated using one of the formulas above. Once the strain of
 578      * the sum is known, the <em>value</em>s of <code>s1</code> and <code>s2</code> are
 579      * then set so that they are have a strain equal to that of the sum. The formulas are
 580      * evaluated so as to take rounding errors into account and ensure that the sum of
 581      * the <em>value</em>s of <code>s1</code> and <code>s2</code> is exactly equal to
 582      * the <em>value</em> of <code>s3</code>.
 583      *
 584      * @return <code>s1+s2</code>: a spring representing <code>s1</code> and <code>s2</code> in series
 585      *
 586      * @see Spring
 587      */
 588      public static Spring sum(Spring s1, Spring s2) {
 589          return new SumSpring(s1, s2);
 590      }
 591 
 592     /**
 593      * Returns <code>max(s1, s2)</code>: a spring whose value is always greater than (or equal to)
 594      *         the values of both <code>s1</code> and <code>s2</code>.
 595      *
 596      * @return <code>max(s1, s2)</code>: a spring whose value is always greater than (or equal to)
 597      *         the values of both <code>s1</code> and <code>s2</code>
 598      * @see Spring
 599      */
 600     public static Spring max(Spring s1, Spring s2) {
 601         return new MaxSpring(s1, s2);
 602     }
 603 
 604     // Remove these, they're not used often and can be created using minus -
 605     // as per these implementations.
 606 
 607     /*pp*/ static Spring difference(Spring s1, Spring s2) {
 608         return sum(s1, minus(s2));
 609     }
 610 
 611     /*
 612     public static Spring min(Spring s1, Spring s2) {
 613         return minus(max(minus(s1), minus(s2)));
 614     }
 615     */
 616 
 617     /**
 618      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 619      * and <em>value</em> properties are each multiples of the properties of the
 620      * argument spring, <code>s</code>. Minimum and maximum properties are
 621      * swapped when <code>factor</code> is negative (in accordance with the
 622      * rules of interval arithmetic).
 623      * <p>
 624      * When factor is, for example, 0.5f the result represents 'the mid-point'
 625      * of its input - an operation that is useful for centering components in
 626      * a container.
 627      *
 628      * @param s the spring to scale
 629      * @param factor amount to scale by.
 630      * @return  a spring whose properties are those of the input spring <code>s</code>
 631      * multiplied by <code>factor</code>
 632      * @throws NullPointerException if <code>s</code> is null
 633      * @since 1.5
 634      */
 635     public static Spring scale(Spring s, float factor) {
 636         checkArg(s);
 637         return new ScaleSpring(s, factor);
 638     }
 639 
 640     /**
 641      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 642      * and <em>value</em> properties are defined by the widths of the <em>minimumSize</em>,
 643      * <em>preferredSize</em>, <em>maximumSize</em> and <em>size</em> properties
 644      * of the supplied component. The returned spring is a 'wrapper' implementation
 645      * whose methods call the appropriate size methods of the supplied component.
 646      * The minimum, preferred, maximum and value properties of the returned spring
 647      * therefore report the current state of the appropriate properties in the
 648      * component and track them as they change.
 649      *
 650      * @param c Component used for calculating size
 651      * @return  a spring whose properties are defined by the horizontal component
 652      * of the component's size methods.
 653      * @throws NullPointerException if <code>c</code> is null
 654      * @since 1.5
 655      */
 656     public static Spring width(Component c) {
 657         checkArg(c);
 658         return new WidthSpring(c);
 659     }
 660 
 661     /**
 662      * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em>
 663      * and <em>value</em> properties are defined by the heights of the <em>minimumSize</em>,
 664      * <em>preferredSize</em>, <em>maximumSize</em> and <em>size</em> properties
 665      * of the supplied component. The returned spring is a 'wrapper' implementation
 666      * whose methods call the appropriate size methods of the supplied component.
 667      * The minimum, preferred, maximum and value properties of the returned spring
 668      * therefore report the current state of the appropriate properties in the
 669      * component and track them as they change.
 670      *
 671      * @param c Component used for calculating size
 672      * @return  a spring whose properties are defined by the vertical component
 673      * of the component's size methods.
 674      * @throws NullPointerException if <code>c</code> is null
 675      * @since 1.5
 676      */
 677     public static Spring height(Component c) {
 678         checkArg(c);
 679         return new HeightSpring(c);
 680     }
 681 
 682 
 683     /**
 684      * If <code>s</code> is null, this throws an NullPointerException.
 685      */
 686     private static void checkArg(Object s) {
 687         if (s == null) {
 688             throw new NullPointerException("Argument must not be null");
 689         }
 690     }
 691 }