StringIndexOutOfBoundsException error from stringbuilder within a while loop

Question

The assignment is to, for example, remove char 'a' from the String "I am Sam am I Sam", this is a bit code I have so far:

public String removeLetters() {
    String cleaned=sentence;
    StringBuilder builder = new StringBuilder(cleaned);

    while(cleaned.indexOf(lookFor) != -1) {
        builder.deleteCharAt(cleaned.indexOf(lookFor));
    }
    return builder.toString();
}

This method returns fine when there's no while loop (though it only removes one char), but when I run it with the while loop I get the OutOfBounds error.

Piovezan · Accepted Answer · 2013-10-24 16:25:01Z

1

Change this:

while(cleaned.indexOf(lookFor) != -1) {
    builder.deleteCharAt(cleaned.indexOf(lookFor));
}

with this:

while(builder.indexOf(Character.toString(lookFor)) != -1) {
    builder.deleteCharAt(builder.indexOf(Character.toString(lookFor)));
}

answered Oct 24, 2013 at 16:25

Piovezan

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2 Comments

jciecka Over a year ago

That did the trick! Thanks for that, now onto trying to understand why, but that's for another day. Thanks again! Edit: turns out I just didn't know what the Character class was.

Piovezan Over a year ago

You must have already done that, but anyway just be sure to notice that I changed your cleaned references for builder, as other members mentioned. Character.toString() is just an utility method for converting a character (which is considered a numeric value in Java) into a string.

Rohit Jain · Accepted Answer · 2013-10-24 16:25:16Z

1

You can directly do this using String#replace method:

String cleaned = "I am Sam am I Sam";
cleaned = cleaned.replace("a", "");
System.out.println(cleaned);   // I m Sm m I Sm

answered Oct 24, 2013 at 16:25

Rohit Jain

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4 Comments

Melih Altıntaş Over a year ago

I think you should use replaceall instead of replace.OP wants to change the all of a

Rohit Jain Over a year ago

@MelihAltıntaş replace replaces all the occurrences only. replaceAll is for regex replacement. That's the only difference.

Melih Altıntaş Over a year ago

Thanks, sorry for my wrong knowledge :) I have already upvoted :)

Rohit Jain Over a year ago

@MelihAltıntaş No issues. :)

Mureinik · Accepted Answer · 2013-10-24 16:25:56Z

0

The condition in the while loop is the index in the cleaned StringBuilder, but then you're using the same index to delete characters from builder - after the first character has been deleted, they no longer match.

In short:

public String removeLetters() {
    String cleaned=sentence;
    StringBuilder builder = new StringBuilder(cleaned);

    while(builder.indexOf(lookFor) != -1) {
        builder.deleteCharAt(builder.indexOf(lookFor));
    }

    return builder.toString();
}

answered Oct 24, 2013 at 16:25

Mureinik

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Comments

Prabhakaran Ramaswamy · Accepted Answer · 2013-10-24 16:27:36Z

0

try this one.

cleaned.replaceAll(lookFor,"");

answered Oct 24, 2013 at 16:27

Prabhakaran Ramaswamy

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Comments

sdanzig · Accepted Answer · 2013-10-24 16:34:32Z

0

Have to remove from the builder, not the source string. Also, you initially had an infinite loop, attempting to modify the builder string, but only checking the source string, which wouldn't change. This compiled and ran fine:

public String removeLetters()
{
    String lookFor = "a";
    String original="I am Sam am I Sam";
    StringBuilder builder = new StringBuilder(original);
    while(builder.indexOf(lookFor) != -1) {
        builder.deleteCharAt(builder.indexOf(lookFor));
    }
    return builder.toString();
}

answered Oct 24, 2013 at 16:34

sdanzig

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