IndexOutOfBoundException on StringBuilder

Question

I'm trying to replace pi with *pi using the following code, however it throws totally unexpected exception. How is the matcher looking at an index higher then String length?

private void makeEvaluationStringExpressionMXParserCompliant() {
        Pattern multiply = Pattern.compile(mContext.getString(R.string.string_multiply));
        Pattern pi = Pattern.compile(mContext.getString(R.string.string_pie));
        Pattern e = Pattern.compile(mContext.getString(R.string.string_e));

        Log.e("wingoku", "pi: "+ pi.toString() + " completeString: "+ mEvaluationStringExpressionBuilder.toString());

       replaceAll(mEvaluationStringExpressionBuilder, pi, "*pi");
    }

    private void replaceAll(StringBuilder sb, Pattern pattern, String replacement) {
        Matcher m = pattern.matcher(sb);
        int start = 0;
        while (m.find(start)) {
            sb.replace(m.start(), m.end(), replacement);
            start = m.start() + replacement.length();
        }
    }

Exception:

 java.lang.IndexOutOfBoundsException: start=3; length=2
                                                     at java.util.regex.Matcher.find(Matcher.java:339)
                                                     at com.app.calculator.utils.StringExpressionFactory.replaceAll(StringExpressionFactory.java:68)
                                                     at com.app.calculator.utils.StringExpressionFactory.makeEvaluationStringExpressionMXParserCompliant(StringExpressionFactory.java:61)
                                                     at com.app.calculator.utils.StringExpressionFactory.createExpression(StringExpressionFactory.java:31)

It is clear that the length of the string is less than then start value. So its causing the error — Hari Lamichhane
– Hari Lamichhane, Commented Mar 25, 2017 at 23:46

Sergey Kalinichenko · Accepted Answer · 2017-03-25 23:53:33Z

2

The problem is that you are passing an initial index that is beyond the length of the string in which you are trying to find a match. Method documentation states the following:

Throws: IndexOutOfBoundsException - If start is less than zero or if start is greater than the length of the input sequence.

You need to add a check to see if the initial index is valid:

while (start < sb.length() && m.find(start)) {
    sb.replace(m.start(), m.end(), replacement);
    start = m.start() + replacement.length();
}

answered Mar 25, 2017 at 23:53

Sergey Kalinichenko

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Comments

redAllocator · Accepted Answer · 2017-03-26 00:07:03Z

0

you have a mistake about start position. you can check it. following source code :

public static void replaceAll(StringBuilder sb, Pattern pattern, String replacement) {
Matcher m = pattern.matcher(sb);
while(m.find()) {
    sb.replace(m.start(), m.end(), replacement);
}

}

and you'd better write a code. you don't need to make replaceAll Function

 StrBuilder replaceAll(char search, char replace)

Replaces the search character with the replace character throughout the builder.

https://commons.apache.org/proper/commons-lang/javadocs/api-3.1/org/apache/commons/lang3/text/StrBuilder.html#replaceAll(java.lang.String,%20java.lang.String)

answered Mar 26, 2017 at 0:07

redAllocator

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