Android Bug? : String.substring(5).replace(“”, “”) // empty string

Question

Here is my code:

String str = \"just_a_string\";
System.out.println(\"]\" + str + \"[\");
System.out.println(\"]\" + str.replace(\"\", \"\") + \"[\");
System         


        

Answer 1

Bingo! i have found the bug!

Thanks @izht for providing the link of the source code. i have located the bug regarding this problem.

This only happens when the String's backing array is having a different (longer) value than the actual String. In particular, when the String.offset (private variable) is larger than zero.

Here's the fix:

public String replace(CharSequence target, CharSequence replacement) {
    if (target == null) {
        throw new NullPointerException("target == null");
    }
    if (replacement == null) {
        throw new NullPointerException("replacement == null");
    }

    String targetString = target.toString();
    int matchStart = indexOf(targetString, 0);
    if (matchStart == -1) {
        // If there's nothing to replace, return the original string untouched.
        return this;
    }

    String replacementString = replacement.toString();

    // The empty target matches at the start and end and between each character.
    int targetLength = targetString.length();
    if (targetLength == 0) {
        int resultLength = (count + 2) * replacementString.length();
        StringBuilder result = new StringBuilder(resultLength);
        result.append(replacementString);
//        for (int i = offset; i < count; ++i) {             // original, bug
        for (int i = offset; i < (count + offset); ++i) {    // fix
            result.append(value[i]);
            result.append(replacementString);
        }
        return result.toString();
    }

    StringBuilder result = new StringBuilder(count);
    int searchStart = 0;
    do {
        // Copy characters before the match...
        result.append(value, offset + searchStart, matchStart - searchStart);
        // Insert the replacement...
        result.append(replacementString);
        // And skip over the match...
        searchStart = matchStart + targetLength;
    } while ((matchStart = indexOf(targetString, searchStart)) != -1);
    // Copy any trailing chars...
    result.append(value, offset + searchStart, count - searchStart);
    return result.toString();
}

i am not sure why Android has to alter (and altered wrongly) the replace() in this way. The original Java implementation doesn't have this issue.

By-the-way, what's now? What can i do with it? (other than using replace() with extra care, or throw away my Android phones :-/)

---

Btw i m quite sure my LG E720 Optimus Chic (Android 2.2) is using a different source code than that one. It keeps halting (suspect infinite looping) upon String.replace() with an empty target string. Lately i found it throws this error message:

05-10 16:41:13.155: E/AndroidRuntime(9384): FATAL EXCEPTION: main
05-10 16:41:13.155: E/AndroidRuntime(9384): java.lang.OutOfMemoryError
05-10 16:41:13.155: E/AndroidRuntime(9384):   at java.lang.AbstractStringBuilder.enlargeBuffer(AbstractStringBuilder.java:97)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at java.lang.AbstractStringBuilder.append0(AbstractStringBuilder.java:157)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at java.lang.StringBuilder.append(StringBuilder.java:217)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at java.lang.String.replace(String.java:1497)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at com.example.testprojectnew.MainActivity.onCreate(MainActivity.java:22)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at android.app.ActivityThread.access$2300(ActivityThread.java:125)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at android.os.Handler.dispatchMessage(Handler.java:99)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at android.os.Looper.loop(Looper.java:123)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at android.app.ActivityThread.main(ActivityThread.java:4627)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at java.lang.reflect.Method.invokeNative(Native Method)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at java.lang.reflect.Method.invoke(Method.java:521)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:878)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:636)
05-10 16:41:13.155: E/AndroidRuntime(9384):   at dalvik.system.NativeStart.main(Native Method)

---

At a second thought, if that for-loop thingy is the bug. It should be a compile time issue. Why would it act differently in different phones (different versions of Android)?

---

Complete Workaround

Got an update from Google, that they have patched it, and will correct it in the future release.

Meanwhile, i have written a patched method, based on their code:

(This is necessary because (1) we still have to wait for the correct release, (2) we need to take care of devices that didnt make that fixed update)

/** Patch for the String.replace(CharSequence target, CharSequence replacement),
 *  because the original is buggy when CharSequence target is empty, i.e. "".
 *  Patched by Google Android: https://android-review.googlesource.com/58393
 */
public static String replacePatched(final String string, final CharSequence target, final CharSequence replacement) {
    if (target == null) {
        throw new NullPointerException("target == null");
    }
    if (replacement == null) {
        throw new NullPointerException("replacement == null");
    }

    final String targetString = target.toString();
    int matchStart = string.indexOf(targetString, 0);
    if (matchStart == -1) {
        // If there's nothing to replace, return the original string untouched.
        return new String(string);
    }

    final char[] value = string.toCharArray();                              // required in patch
    final int count = value.length;                                         // required in patch

    final String replacementString = replacement.toString();

    // The empty target matches at the start and end and between each character.
    if (targetString.length() == 0) {
        // The result contains the original 'count' characters, a copy of the
        // replacement string before every one of those characters, and a final
        // copy of the replacement string at the end.
        final StringBuilder result = new StringBuilder(count + (count + 1) * replacementString.length());
        result.append(replacementString);
        for (int i = 0; i < count; ++i) {
            result.append(value[i]);
            result.append(replacementString);
        }
        return new String(result);      // StringBuilder.toString() does not give exact length
    }

    final StringBuilder result = new StringBuilder(count);
    int searchStart = 0;
    do {
        // Copy characters before the match...
        result.append(value, searchStart, matchStart - searchStart);
        // Insert the replacement...
        result.append(replacementString);
        // And skip over the match...
        searchStart = matchStart + targetString.length();
    } while ((matchStart = string.indexOf(targetString, searchStart)) != -1);
    // Copy any trailing chars...
    result.append(value, searchStart, count - searchStart);
    return new String(result);          // StringBuilder.toString() does not give exact length
}

The verbose version:

/** Patch for the String.replace(CharSequence target, CharSequence replacement),
 *  because the original is buggy when CharSequence target is empty, i.e. "".
 *  Patched by Google Android: https://android-review.googlesource.com/58393
 */
public static String replacePatched(final String string, final CharSequence target, final CharSequence replacement) {
    if (target == null) {
        throw new NullPointerException("target == null");
    }
    if (replacement == null) {
        throw new NullPointerException("replacement == null");
    }

//    String targetString = target.toString();                                    // original
    final String targetString = target.toString();
//    int matchStart = indexOf(targetString, 0);                                  // original
    int matchStart = string.indexOf(targetString, 0);
    if (matchStart == -1) {
        // If there's nothing to replace, return the original string untouched.
//        return this;                                                            // original
        return new String(string);
    }

    final char[] value = string.toCharArray();                              // required in patch
    final int count = value.length;                                         // required in patch

//    String replacementString = replacement.toString();                          // original
    final String replacementString = replacement.toString();

    // The empty target matches at the start and end and between each character.
//    int targetLength = targetString.length();                                   // original
//    if (targetLength == 0) {                                                    // original
    if (targetString.length() == 0) {
//        int resultLength = (count + 2) * replacementString.length();            // original
//        // The result contains the original 'count' characters, a copy of the
//        // replacement string before every one of those characters, and a final
//        // copy of the replacement string at the end.
//        int resultLength = count + (count + 1) * replacementString.length();    // patched by Google Android
//        StringBuilder result = new StringBuilder(resultLength);                 // original
        final StringBuilder result = new StringBuilder(count + (count + 1) * replacementString.length());
        result.append(replacementString);
//        for (int i = offset; i < count; ++i) {                                  // original
//        int end = offset + count;                                               // patched by Google Android
//        for (int i = offset; i != end; ++i) {                                   // patched by Google Android
        for (int i = 0; i < count; ++i) {
            result.append(value[i]);
            result.append(replacementString);
        }
//        return result.toString();                                               // original
        return new String(result);      // StringBuilder.toString() does not give exact length
    }

//    StringBuilder result = new StringBuilder(count);                            // original
    final StringBuilder result = new StringBuilder(count);
    int searchStart = 0;
    do {
        // Copy characters before the match...
//        result.append(value, offset + searchStart, matchStart - searchStart);   // original
        result.append(value, searchStart, matchStart - searchStart);
        // Insert the replacement...
        result.append(replacementString);
        // And skip over the match...
//        searchStart = matchStart + targetLength;                                // original
        searchStart = matchStart + targetString.length();
//    } while ((matchStart = indexOf(targetString, searchStart)) != -1);          // original
    } while ((matchStart = string.indexOf(targetString, searchStart)) != -1);
    // Copy any trailing chars...
//    result.append(value, offset + searchStart, count - searchStart);            // original
    result.append(value, searchStart, count - searchStart);
//    return result.toString();                                                   // original
    return new String(result);          // StringBuilder.toString() does not give exact length
}