1 /*
2  * Written by Martin Buchholz with assistance from members of JCP
3  * JSR-166 Expert Group and released to the public domain, as
4  * explained at http://creativecommons.org/publicdomain/zero/1.0/
5  */
6 
7 package java.util.concurrent;
8 
9 import java.util.Collection;
10 
11 /** Shared implementation code for java.util.concurrent. */
12 class Helpers {
Helpers()13     private Helpers() {}                // non-instantiable
14 
15     /**
16      * An implementation of Collection.toString() suitable for classes
17      * with locks.  Instead of holding a lock for the entire duration of
18      * toString(), or acquiring a lock for each call to Iterator.next(),
19      * we hold the lock only during the call to toArray() (less
20      * disruptive to other threads accessing the collection) and follows
21      * the maxim "Never call foreign code while holding a lock".
22      */
collectionToString(Collection<?> c)23     static String collectionToString(Collection<?> c) {
24         final Object[] a = c.toArray();
25         final int size = a.length;
26         if (size == 0)
27             return "[]";
28         int charLength = 0;
29 
30         // Replace every array element with its string representation
31         for (int i = 0; i < size; i++) {
32             Object e = a[i];
33             // Extreme compatibility with AbstractCollection.toString()
34             String s = (e == c) ? "(this Collection)" : objectToString(e);
35             a[i] = s;
36             charLength += s.length();
37         }
38 
39         return toString(a, size, charLength);
40     }
41 
42     /**
43      * Like Arrays.toString(), but caller guarantees that size > 0,
44      * each element with index 0 <= i < size is a non-null String,
45      * and charLength is the sum of the lengths of the input Strings.
46      */
toString(Object[] a, int size, int charLength)47     static String toString(Object[] a, int size, int charLength) {
48         // assert a != null;
49         // assert size > 0;
50 
51         // Copy each string into a perfectly sized char[]
52         // Length of [ , , , ] == 2 * size
53         final char[] chars = new char[charLength + 2 * size];
54         chars[0] = '[';
55         int j = 1;
56         for (int i = 0; i < size; i++) {
57             if (i > 0) {
58                 chars[j++] = ',';
59                 chars[j++] = ' ';
60             }
61             String s = (String) a[i];
62             int len = s.length();
63             s.getChars(0, len, chars, j);
64             j += len;
65         }
66         chars[j] = ']';
67         // assert j == chars.length - 1;
68         return new String(chars);
69     }
70 
71     /** Optimized form of: key + "=" + val */
mapEntryToString(Object key, Object val)72     static String mapEntryToString(Object key, Object val) {
73         final String k, v;
74         final int klen, vlen;
75         final char[] chars =
76             new char[(klen = (k = objectToString(key)).length()) +
77                      (vlen = (v = objectToString(val)).length()) + 1];
78         k.getChars(0, klen, chars, 0);
79         chars[klen] = '=';
80         v.getChars(0, vlen, chars, klen + 1);
81         return new String(chars);
82     }
83 
objectToString(Object x)84     private static String objectToString(Object x) {
85         // Extreme compatibility with StringBuilder.append(null)
86         String s;
87         return (x == null || (s = x.toString()) == null) ? "null" : s;
88     }
89 }
90