File sorting, Comparison method violates its general contract
- by user2677383
My file sorting comparator sometimes invoke java.lang.IllegalArgumentException in android app.
I cannot figure out the reason. could you explain that?
here is my code block:
Comparator cc = new Comparator<File>() {
@Override
public int compare(File f1, File f2) {
if (f1.isDirectory() && !f2.isDirectory()) {
return 1;
}
if (f2.isDirectory() && !f1.isDirectory()) {
return -1;
}
if ((f1.isFile() && f2.isFile()) || (f1.isDirectory() && f2.isDirectory())) {
if (sort == 1) {
return Util.compareFileName(f2.getName(), f1.getName());
} else if (sort == 2) {
return (int) (f1.lastModified() - f2.lastModified());
} else if (sort == 3) {
return (int) (f2.lastModified() - f1.lastModified());
} else if (sort == 4) {
return (int) (f1.length() - f2.length());
} else if (sort == 5) {
return (int) (f2.length() - f1.length());
} else
return Util.compareFileName(f1.getName(), f2.getName());
}
return f1.compareTo(f2);
}
};
Util.compareFileName is as followings:
public static int compareFileName(String s1, String s2) {
int thisMarker = 0;
int thatMarker = 0;
int s1Length = s1.length();
int s2Length = s2.length();
while (thisMarker < s1Length && thatMarker < s2Length) {
String thisChunk = getChunk(s1, s1Length, thisMarker);
thisMarker += thisChunk.length();
String thatChunk = getChunk(s2, s2Length, thatMarker);
thatMarker += thatChunk.length();
// If both chunks contain numeric characters, sort them numerically
int result = 0;
if (isDigit(thisChunk.charAt(0)) && isDigit(thatChunk.charAt(0))) {
// Simple chunk comparison by length.
int thisChunkLength = thisChunk.length();
result = thisChunkLength - thatChunk.length();
// If equal, the first different number counts
if (result == 0) {
for (int i = 0; i < thisChunkLength; i++) {
result = thisChunk.charAt(i) - thatChunk.charAt(i);
if (result != 0) {
return result;
}
}
}
} else {
result = thisChunk.compareTo(thatChunk);
}
if (result != 0)
return result;
}
return s1Length - s2Length;
}
