public static int indexOfDifference(String[] strs) {
        if (strs == null || strs.length <= 1) {
            return INDEX_NOT_FOUND;
        }
        boolean anyStringNull = false;
        boolean allStringsNull = true;
        int arrayLen = strs.length;
        int shortestStrLen = Integer.MAX_VALUE;
        int longestStrLen = 0;

        // find the min and max string lengths; this avoids checking to make
        // sure we are not exceeding the length of the string each time through
        // the bottom loop.
        for (int i = 0; i < arrayLen; i++) {
            if (strs[i] == null) {
                anyStringNull = true;
                shortestStrLen = 0;
            } else {
                allStringsNull = false;
                shortestStrLen = Math.min(strs[i].length(), shortestStrLen);
                longestStrLen = Math.max(strs[i].length(), longestStrLen);
            }
        }

        // handle lists containing all nulls or all empty strings
        if (allStringsNull || (longestStrLen == 0 && !anyStringNull)) {
            return INDEX_NOT_FOUND;
        }

        // handle lists containing some nulls or some empty strings
        if (shortestStrLen == 0) {
            return 0;
        }

        // find the position with the first difference across all strings
        int firstDiff = -1;
        for (int stringPos = 0; stringPos < shortestStrLen; stringPos++) {
            char comparisonChar = strs[0].charAt(stringPos);
            for (int arrayPos = 1; arrayPos < arrayLen; arrayPos++) {
                if (strs[arrayPos].charAt(stringPos) != comparisonChar) {
                    firstDiff = stringPos;
                    break;
                }
            }
            if (firstDiff != -1) {
                break;
            }
        }

        if (firstDiff == -1 && shortestStrLen != longestStrLen) {
            // we compared all of the characters up to the length of the
            // shortest string and didn't find a match, but the string lengths
            // vary, so return the length of the shortest string.
            return shortestStrLen;
        }
        return firstDiff;
    }
public static int indexOfDifference ( String [ ] strs ) { if ( strs == null || strs . length <= 1 ) { return INDEX_NOT_FOUND ; } boolean anyStringNull = false ; boolean allStringsNull = true ; int arrayLen = strs . length ; int shortestStrLen = Integer . MAX_VALUE ; int longestStrLen = 0 ; for ( int i = 0 ; i < arrayLen ; i ++ ) { if ( strs [ i ] == null ) { anyStringNull = true ; shortestStrLen = 0 ; } else { allStringsNull = false ; shortestStrLen = Math . min ( strs [ i ] . length ( ) , shortestStrLen ) ; longestStrLen = Math . max ( strs [ i ] . length ( ) , longestStrLen ) ; } } if ( allStringsNull || ( longestStrLen == 0 && ! anyStringNull ) ) { return INDEX_NOT_FOUND ; } if ( shortestStrLen == 0 ) { return 0 ; } int firstDiff = - 1 ; for ( int stringPos = 0 ; stringPos < shortestStrLen ; stringPos ++ ) { char comparisonChar = strs [ 0 ] . charAt ( stringPos ) ; for ( int arrayPos = 1 ; arrayPos < arrayLen ; arrayPos ++ ) { if ( strs [ arrayPos ] . charAt ( stringPos ) != comparisonChar ) { firstDiff = stringPos ; break ; } } if ( firstDiff != - 1 ) { break ; } } if ( firstDiff == - 1 && shortestStrLen != longestStrLen ) { return shortestStrLen ; } return firstDiff ; }
<p>Compares all Strings in an array and returns the index at which the
Strings begin to differ.</p>

<p>For example,
<code>indexOfDifference(new String[] {"i am a machine", "i am a robot"}) -> 7</code></p>

<pre>
StringUtils.indexOfDifference(null) = -1
StringUtils.indexOfDifference(new String[] {}) = -1
StringUtils.indexOfDifference(new String[] {"abc"}) = -1
StringUtils.indexOfDifference(new String[] {null, null}) = -1
StringUtils.indexOfDifference(new String[] {"", ""}) = -1
StringUtils.indexOfDifference(new String[] {"", null}) = 0
StringUtils.indexOfDifference(new String[] {"abc", null, null}) = 0
StringUtils.indexOfDifference(new String[] {null, null, "abc"}) = 0
StringUtils.indexOfDifference(new String[] {"", "abc"}) = 0
StringUtils.indexOfDifference(new String[] {"abc", ""}) = 0
StringUtils.indexOfDifference(new String[] {"abc", "abc"}) = -1
StringUtils.indexOfDifference(new String[] {"abc", "a"}) = 1
StringUtils.indexOfDifference(new String[] {"ab", "abxyz"}) = 2
StringUtils.indexOfDifference(new String[] {"abcde", "abxyz"}) = 2
StringUtils.indexOfDifference(new String[] {"abcde", "xyz"}) = 0
StringUtils.indexOfDifference(new String[] {"xyz", "abcde"}) = 0
StringUtils.indexOfDifference(new String[] {"i am a machine", "i am a robot"}) = 7
</pre>

@param strs  array of strings, entries may be null
@return the index where the strings begin to differ; -1 if they are all equal
@since 2.4