问题
Is the indexOf(String) method case sensitive? If so, is there a case insensitive version of it?
回答1:
The indexOf() methods are all case-sensitive. You can make them (roughly, in a broken way, but working for plenty of cases) case-insensitive by converting your strings to upper/lower case beforehand:
s1 = s1.toLowerCase(Locale.US);
s2 = s2.toLowerCase(Locale.US);
s1.indexOf(s2);
回答2:
Is the indexOf(String) method case sensitive?
Yes, it is case sensitive:
@Test
public void indexOfIsCaseSensitive() {
assertTrue("Hello World!".indexOf("Hello") != -1);
assertTrue("Hello World!".indexOf("hello") == -1);
}
If so, is there a case insensitive version of it?
No, there isn't. You can convert both strings to lower case before calling indexOf:
@Test
public void caseInsensitiveIndexOf() {
assertTrue("Hello World!".toLowerCase().indexOf("Hello".toLowerCase()) != -1);
assertTrue("Hello World!".toLowerCase().indexOf("hello".toLowerCase()) != -1);
}
回答3:
There is an ignore case method in StringUtils class of Apache Commons Lang library
indexOfIgnoreCase(CharSequence str, CharSequence searchStr)
回答4:
Yes, indexOf is case sensitive.
The best way to do case insensivity I have found is:
String original;
int idx = original.toLowerCase().indexOf(someStr.toLowerCase());
That will do a case insensitive indexOf().
回答5:
Here is my solution which does not allocate any heap memory, therefore it should be significantly faster than most of the other implementations mentioned here.
public static int indexOfIgnoreCase(final String haystack,
final String needle) {
if (needle.isEmpty() || haystack.isEmpty()) {
// Fallback to legacy behavior.
return haystack.indexOf(needle);
}
for (int i = 0; i < haystack.length(); ++i) {
// Early out, if possible.
if (i + needle.length() > haystack.length()) {
return -1;
}
// Attempt to match substring starting at position i of haystack.
int j = 0;
int ii = i;
while (ii < haystack.length() && j < needle.length()) {
char c = Character.toLowerCase(haystack.charAt(ii));
char c2 = Character.toLowerCase(needle.charAt(j));
if (c != c2) {
break;
}
j++;
ii++;
}
// Walked all the way to the end of the needle, return the start
// position that this was found.
if (j == needle.length()) {
return i;
}
}
return -1;
}
And here are the unit tests that verify correct behavior.
@Test
public void testIndexOfIgnoreCase() {
assertThat(StringUtils.indexOfIgnoreCase("A", "A"), is(0));
assertThat(StringUtils.indexOfIgnoreCase("a", "A"), is(0));
assertThat(StringUtils.indexOfIgnoreCase("A", "a"), is(0));
assertThat(StringUtils.indexOfIgnoreCase("a", "a"), is(0));
assertThat(StringUtils.indexOfIgnoreCase("a", "ba"), is(-1));
assertThat(StringUtils.indexOfIgnoreCase("ba", "a"), is(1));
assertThat(StringUtils.indexOfIgnoreCase("Royal Blue", " Royal Blue"), is(-1));
assertThat(StringUtils.indexOfIgnoreCase(" Royal Blue", "Royal Blue"), is(1));
assertThat(StringUtils.indexOfIgnoreCase("Royal Blue", "royal"), is(0));
assertThat(StringUtils.indexOfIgnoreCase("Royal Blue", "oyal"), is(1));
assertThat(StringUtils.indexOfIgnoreCase("Royal Blue", "al"), is(3));
assertThat(StringUtils.indexOfIgnoreCase("", "royal"), is(-1));
assertThat(StringUtils.indexOfIgnoreCase("Royal Blue", ""), is(0));
assertThat(StringUtils.indexOfIgnoreCase("Royal Blue", "BLUE"), is(6));
assertThat(StringUtils.indexOfIgnoreCase("Royal Blue", "BIGLONGSTRING"), is(-1));
assertThat(StringUtils.indexOfIgnoreCase("Royal Blue", "Royal Blue LONGSTRING"), is(-1));
}
回答6:
Yes, it is case-sensitive. You can do a case-insensitive indexOf by converting your String and the String parameter both to upper-case before searching.
String str = "Hello world";
String search = "hello";
str.toUpperCase().indexOf(search.toUpperCase());
Note that toUpperCase may not work in some circumstances. For instance this:
String str = "Feldbergstraße 23, Mainz";
String find = "mainz";
int idxU = str.toUpperCase().indexOf (find.toUpperCase ());
int idxL = str.toLowerCase().indexOf (find.toLowerCase ());
idxU will be 20, which is wrong! idxL will be 19, which is correct. What's causing the problem is tha toUpperCase() converts the "ß" character into TWO characters, "SS" and this throws the index off.
Consequently, always stick with toLowerCase()
回答7:
What are you doing with the index value once returned?
If you are using it to manipulate your string, then could you not use a regular expression instead?
import static org.junit.Assert.assertEquals;
import org.junit.Test;
public class StringIndexOfRegexpTest {
@Test
public void testNastyIndexOfBasedReplace() {
final String source = "Hello World";
final int index = source.toLowerCase().indexOf("hello".toLowerCase());
final String target = "Hi".concat(source.substring(index
+ "hello".length(), source.length()));
assertEquals("Hi World", target);
}
@Test
public void testSimpleRegexpBasedReplace() {
final String source = "Hello World";
final String target = source.replaceFirst("(?i)hello", "Hi");
assertEquals("Hi World", target);
}
}
回答8:
I've just looked at the source. It compares chars so it is case sensitive.
回答9:
@Test
public void testIndexofCaseSensitive() {
TestCase.assertEquals(-1, "abcDef".indexOf("d") );
}
回答10:
Yes, I am fairly sure it is. One method of working around that using the standard library would be:
int index = str.toUpperCase().indexOf("FOO");
回答11:
Had the same problem. I tried regular expression and the apache StringUtils.indexOfIgnoreCase-Method, but both were pretty slow... So I wrote an short method myself...:
public static int indexOfIgnoreCase(final String chkstr, final String searchStr, int i) {
if (chkstr != null && searchStr != null && i > -1) {
int serchStrLength = searchStr.length();
char[] searchCharLc = new char[serchStrLength];
char[] searchCharUc = new char[serchStrLength];
searchStr.toUpperCase().getChars(0, serchStrLength, searchCharUc, 0);
searchStr.toLowerCase().getChars(0, serchStrLength, searchCharLc, 0);
int j = 0;
for (int checkStrLength = chkstr.length(); i < checkStrLength; i++) {
char charAt = chkstr.charAt(i);
if (charAt == searchCharLc[j] || charAt == searchCharUc[j]) {
if (++j == serchStrLength) {
return i - j + 1;
}
} else { // faster than: else if (j != 0) {
i = i - j;
j = 0;
}
}
}
return -1;
}
According to my tests its much faster... (at least if your searchString is rather short). if you have any suggestions for improvement or bugs it would be nice to let me know... (since I use this code in an application ;-)
回答12:
The first question has already been answered many times. Yes, the String.indexOf() methods are all case-sensitive.
If you need a locale-sensitive indexOf() you could use the Collator. Depending on the strength value you set you can get case insensitive comparison, and also treat accented letters as the same as the non-accented ones, etc.
Here is an example of how to do this:
private int indexOf(String original, String search) {
Collator collator = Collator.getInstance();
collator.setStrength(Collator.PRIMARY);
for (int i = 0; i <= original.length() - search.length(); i++) {
if (collator.equals(search, original.substring(i, i + search.length()))) {
return i;
}
}
return -1;
}
回答13:
Just to sum it up, 3 solutions:
- using toLowerCase() or toUpperCase
- using StringUtils of apache
- using regex
Now, what I was wondering was which one is the fastest? I'm guessing on average the first one.
回答14:
But it's not hard to write one:
public class CaseInsensitiveIndexOfTest extends TestCase {
public void testOne() throws Exception {
assertEquals(2, caseInsensitiveIndexOf("ABC", "xxabcdef"));
}
public static int caseInsensitiveIndexOf(String substring, String string) {
return string.toLowerCase().indexOf(substring.toLowerCase());
}
}
回答15:
Converting both strings to lower-case is usually not a big deal but it would be slow if some of the strings is long. And if you do this in a loop then it would be really bad. For this reason, I would recommend indexOfIgnoreCase.
回答16:
static string Search(string factMessage, string b)
{
int index = factMessage.IndexOf(b, StringComparison.CurrentCultureIgnoreCase);
string line = null;
int i = index;
if (i == -1)
{ return "not matched"; }
else
{
while (factMessage[i] != ' ')
{
line = line + factMessage[i];
i++;
}
return line;
}
}
回答17:
Here's a version closely resembling Apache's StringUtils version:
public int indexOfIgnoreCase(String str, String searchStr) {
return indexOfIgnoreCase(str, searchStr, 0);
}
public int indexOfIgnoreCase(String str, String searchStr, int fromIndex) {
// https://stackoverflow.com/questions/14018478/string-contains-ignore-case/14018511
if(str == null || searchStr == null) return -1;
if (searchStr.length() == 0) return fromIndex; // empty string found; use same behavior as Apache StringUtils
final int endLimit = str.length() - searchStr.length() + 1;
for (int i = fromIndex; i < endLimit; i++) {
if (str.regionMatches(true, i, searchStr, 0, searchStr.length())) return i;
}
return -1;
}
回答18:
indexOf is case sensitive. This is because it uses the equals method to compare the elements in the list. The same thing goes for contains and remove.
来源：https://stackoverflow.com/questions/1126227/indexof-case-sensitive