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