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/* |
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* Written by Martin Buchholz with assistance from members of JCP |
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* JSR-166 Expert Group and released to the public domain, as |
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* explained at http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent; |
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|
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import java.util.Collection; |
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|
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/** Shared implementation code for java.util.concurrent. */ |
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class Helpers { |
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/** |
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* An implementation of Collection.toString() suitable for classes |
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* with locks. Instead of holding a lock for the entire duration of |
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* toString(), or acquiring a lock for each call to Iterator.next(), |
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* we hold the lock only during the call to toArray() (less |
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* disruptive to other threads accessing the collection) and follows |
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* the maxim "Never call foreign code while holding a lock". |
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*/ |
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static String collectionToString(Collection<?> c) { |
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final Object[] a = c.toArray(); |
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final int size = a.length; |
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if (size == 0) |
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return "[]"; |
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int charLength = 0; |
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|
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// Replace every array element with its string representation |
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for (int i = 0; i < size; i++) { |
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Object e = a[i]; |
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// Extreme compatibility with AbstractCollection.toString() |
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String s = (e == c) ? "(this Collection)" : objectToString(e); |
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a[i] = s; |
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charLength += s.length(); |
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} |
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|
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return toString(a, size, charLength); |
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} |
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|
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/** |
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* Like Arrays.toString(), but caller guarantees that size > 0, |
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* each element with index 0 <= i < size is a non-null String, |
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* and charLength is the sum of the lengths of the input Strings. |
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*/ |
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static String toString(Object[] a, int size, int charLength) { |
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// assert a != null; |
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// assert size > 0; |
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|
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// Copy each string into a perfectly sized char[] |
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// Length of [ , , , ] == 2 * size |
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final char[] chars = new char[charLength + 2 * size]; |
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chars[0] = '['; |
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int j = 1; |
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for (int i = 0; i < size; i++) { |
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if (i > 0) { |
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chars[j++] = ','; |
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chars[j++] = ' '; |
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} |
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String s = (String) a[i]; |
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int len = s.length(); |
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s.getChars(0, len, chars, j); |
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j += len; |
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} |
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chars[j] = ']'; |
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// assert j == chars.length - 1; |
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return newStringUnsafe(chars); |
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} |
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|
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/** Optimized form of: key + "=" + val */ |
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static String mapEntryToString(Object key, Object val) { |
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final String k, v; |
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final int klen, vlen; |
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final char[] chars = |
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new char[(klen = (k = objectToString(key)).length()) + |
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(vlen = (v = objectToString(val)).length()) + 1]; |
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k.getChars(0, klen, chars, 0); |
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chars[klen] = '='; |
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v.getChars(0, vlen, chars, klen + 1); |
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return newStringUnsafe(chars); |
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} |
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|
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private static String objectToString(Object x) { |
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// Extreme compatibility with StringBuilder.append(null) |
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String s; |
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return (x == null || (s = x.toString()) == null) ? "null" : s; |
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} |
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|
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/** |
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* Returns a String containing the contents of chars, which caller |
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* promises will never be modified. |
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*/ |
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private static String newStringUnsafe(char[] chars) { |
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// If porting to a JDK where sun.misc.SharedSecrets is not |
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// available, modify the code below to simply: |
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// return new String(chars); |
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// TODO: Can we do this more portably? |
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return sun.misc.SharedSecrets.getJavaLangAccess().newStringUnsafe(chars); |
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} |
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|
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} |
