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      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 {
     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      */
     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      */
     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 */
     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 
     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