This is an interesting quirk of the API ... I had no idea.
On Mon, Nov 16, 2009 at 8:03 PM, <jessewil...@apache.org> wrote: > Author: jessewilson > Date: Tue Nov 17 02:03:15 2009 > New Revision: 881092 > > URL: http://svn.apache.org/viewvc?rev=881092&view=rev > Log: > Fixing StringReader to support skipping negative distances. This bizarre > behaviour is required by the spec. > > Modified: > > harmony/enhanced/classlib/trunk/modules/luni/src/main/java/java/io/StringReader.java > > Modified: > harmony/enhanced/classlib/trunk/modules/luni/src/main/java/java/io/StringReader.java > URL: > http://svn.apache.org/viewvc/harmony/enhanced/classlib/trunk/modules/luni/src/main/java/java/io/StringReader.java?rev=881092&r1=881091&r2=881092&view=diff > ============================================================================== > --- > harmony/enhanced/classlib/trunk/modules/luni/src/main/java/java/io/StringReader.java > (original) > +++ > harmony/enhanced/classlib/trunk/modules/luni/src/main/java/java/io/StringReader.java > Tue Nov 17 02:03:15 2009 > @@ -221,13 +221,19 @@ > } > > /** > - * Skips {...@code amount} characters in the source string. Subsequent > calls of > - * {...@code read} methods will not return these characters unless > {...@code > - * reset()} is used. > - * > + * Moves {...@code ns} characters in the source string. Unlike the > {...@link > + * Reader#skip(long) overridden method}, this method may skip negative > skip > + * distances: this rewinds the input so that characters may be read > again. > + * When the end of the source string has been reached, the input cannot > be > + * rewound. > + * > * @param ns > - * the maximum number of characters to skip. > - * @return the number of characters actually skipped or 0 if {...@code > ns < 0}. > + * the maximum number of characters to skip. Positive values > skip > + * forward; negative values skip backward. > + * @return the number of characters actually skipped. This is bounded > below > + * by the number of characters already read and above by the > + * number of characters remaining:<br> {...@code -(num chars > already > + * read) <= distance skipped <= num chars remaining}. > * @throws IOException > * if this reader is closed. > * @see #mark(int) > @@ -240,18 +246,18 @@ > if (isClosed()) { > throw new IOException(Msg.getString("K0083")); //$NON-NLS-1$ > } > - if (ns <= 0) { > - return 0; > - } > - long skipped = 0; > - if (ns < this.count - pos) { > - pos = pos + (int) ns; > - skipped = ns; > - } else { > - skipped = this.count - pos; > - pos = this.count; > + > + int minSkip = -pos; > + int maxSkip = count - pos; > + > + if (maxSkip == 0 || ns > maxSkip) { > + ns = maxSkip; // no rewinding if we're at the end > + } else if (ns < minSkip) { > + ns = minSkip; > } > - return skipped; > + > + pos += ns; > + return ns; > } > } > } > > >
