CollectionUtil


1   package polyglot.util;
2   
3   import java.util.*;
4   
5   /** Collection utilities. */
6   public class CollectionUtil
7   {
8       /** Return a new list with <code>o</code> appended to <code>l</code>. */
9       public static List add(List l, Object   o) {
10          l.add(o);
11          return l;
12      }
13  
14      /**
15       * Return true if <code>a</code> and <code>b</code> are
16       * pointer equal, or if iterators over both return the same
17       * sequence of pointer equal elements.
18       */
19      public static boolean equals(Collection a, Collection b) {
20          if (a == b) {
21              return true;
22          }
23          
24          // the case where both are null is handled in the previous if.
25          if (a == null ^ b == null) {
26              return false;
27          }
28          
29          Iterator i = a.iterator();
30          Iterator j = b.iterator();
31  
32          while (i.hasNext() && j.hasNext()) {
33              Object   o = i.next();
34              Object   p = j.next();
35  
36              if (o != p) {
37                  return false;
38              }
39          }
40  
41          if (i.hasNext() || j.hasNext()) {
42              return false;
43          }
44  
45          return true;
46      }
47  
48      /** Return a singleton list containing <code>o</code>. */
49      public static List list(Object   o) {
50          return Collections.singletonList(o);
51      }
52  
53      /** Return a list containing <code>o1</code> and <code>o2</code>. */
54      public static List list(Object   o1, Object   o2) {
55          List l = new ArrayList(2);
56          l.add(o1);
57          l.add(o2);
58          return l;
59      }
60  
61      /** Return a list containing <code>o1</code>, ..., <code>o3</code>. */
62      public static List list(Object   o1, Object   o2, Object   o3) {
63          List l = new ArrayList(3);
64          l.add(o1);
65          l.add(o2);
66          l.add(o3);
67          return l;
68      }
69  
70      /** Return a list containing <code>o1</code>, ..., <code>o4</code>. */
71      public static List list(Object   o1, Object   o2, Object   o3, Object   o4) {
72          List l = new ArrayList(3);
73          l.add(o1);
74          l.add(o2);
75          l.add(o3);
76          l.add(o4);
77          return l;
78      }
79  
80          public static Object   firstOrElse(Collection l, Object   alt) {
81                  Iterator i = l.iterator();
82                  if (i.hasNext()) return i.next();
83                  return alt;
84          }
85  
86  
87          public static Iterator pairs(Collection l) {
88                  List x = new LinkedList();
89                  Object   prev = null;
90                  for (Iterator i = l.iterator(); i.hasNext(); ) {
91                      Object   curr = i.next();
92                      if (prev != null) x.add(new Object  [] { prev, curr });
93                      prev = curr;
94                  }
95                  return x.iterator();
96          }
97  
98      /**
99       * Apply <code>t</code> to each element of <code>l</code>.
100      * <code>l</code> is not modified.  
101      * @return A list containing the result of each transformation,
102      * in the same order as the original elements.
103      */
104     public static List map(List l, Transformation t) {
105         List m = new ArrayList(l.size());
106         for (Iterator i = new TransformingIterator(l.iterator(), t); 
107             i.hasNext(); )
108         {
109             m.add(i.next());
110         }
111         return m;
112     }
113 
114 }
115
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