Spring


1   package prefuse.util.force;
2   
3   import java.util.ArrayList  ;
4   
5   /**
6    * Represents a spring in a force simulation.
7    *
8    * @author <a HREF="http://jheer.org">jeffrey heer</a>
9    */
10  public class Spring {
11      private static SpringFactory s_factory = new SpringFactory();
12      
13      /**
14       * Retrieve the SpringFactory instance, which serves as an object pool
15       * for Spring instances.
16       * @return the Spring Factory
17       */
18      public static SpringFactory getFactory() {
19          return s_factory;
20      }
21      
22      /**
23       * Create a new Spring instance
24       * @param fi1 the first ForceItem endpoint
25       * @param fi2 the second ForceItem endpoint
26       * @param k the spring tension co-efficient
27       * @param len the spring's resting length
28       */
29      public Spring(ForceItem fi1, ForceItem fi2, float k, float len) {
30          item1 = fi1;
31          item2 = fi2;
32          coeff = k;
33          length = len;
34      }
35      
36      /** The first ForceItem endpoint */
37      public ForceItem item1;
38      /** The second ForceItem endpoint */
39      public ForceItem item2;
40      /** The spring's resting length */
41      public float length;
42      /** The spring tension co-efficient */
43      public float coeff;
44      
45      /**
46       * The SpringFactory is responsible for generating Spring instances
47       * and maintaining an object pool of Springs to reduce garbage collection
48       * overheads while force simulations are running.
49       */
50      public static final class SpringFactory {
51          private int maxSprings = 10000;
52          private ArrayList   springs = new ArrayList  ();
53          
54          /**
55           * Get a Spring instance and set it to the given parameters.
56           */
57          public Spring getSpring(ForceItem f1, ForceItem f2, float k, float length) {
58              if ( springs.size() > 0 ) {
59                  Spring s = (Spring)springs.remove(springs.size()-1);
60                  s.item1 = f1;
61                  s.item2 = f2;
62                  s.coeff = k;
63                  s.length = length;
64                  return s;
65              } else {
66                  return new Spring(f1,f2,k,length);
67              }
68          }
69          /**
70           * Reclaim a Spring into the object pool.
71           */
72          public void reclaim(Spring s) {
73              s.item1 = null;
74              s.item2 = null;
75              if ( springs.size() < maxSprings )
76                  springs.add(s);
77          }
78      } // end of inner class SpringFactory
79  
80  } // end of class Spring
81
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