Java String index out of range : -1

Question

lang.StringIndexOutOfBoundsException for the following code. The program checks for sentences without spaces to extract words which matches the dictionary of valid English words

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

class WordCheckUtil{

boolean dictionaryContains(String word)
{
    List<String> dictionary = new ArrayList<String>(Arrays.asList("mobile","samsung","sam","sung",
                            "man","mango", "icecream","and",
                            "go","i","love","ice","cream"));

        if(dictionary.contains(word))
            return true;

    return false;
}

void wordCheck(String str){
    wordBreakCheck(str,str.length(),"");
}

void wordBreakCheck(String str, int length, String result){
    System.out.println(str+" "+length+" "+result);
    for (int i = 1; i <= length; i++) {
        String prefix = str.substring(0, i);
        System.out.println(prefix);
        if(dictionaryContains(prefix)){

            if(i == length){
                result += prefix;
                System.out.println("--> "+result);
                return;
            }
            System.out.println(i+" -- "+length);
            String subStr = str.substring(i,length-i);
            wordBreakCheck(subStr,length-i,result+prefix+" ");
        }
    }
}

public static void main(String[] args) {
    WordCheckUtil wr = new WordCheckUtil();
    wr.wordCheck("iloveice");
}

}

This is the error stack I am getting:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String 
index out of range: -1
    at java.lang.String.substring(String.java:1967)
    at WordCheckUtil.wordBreakCheck(WrodCheckUtil.java:36)
    at WordCheckUtil.wordBreakCheck(WrodCheckUtil.java:37)
    at WordCheckUtil.wordCheck(WrodCheckUtil.java:20)
    at WordCheckUtil.main(WrodCheckUtil.java:44)

Time to learn to use a debugger -- do this and the problem will become obvious to you. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Apr 13, 2017 at 18:46
I checked the debugger, the values of "i" and "length" before this error is thrown is 4 and 7 — shailbenq
– shailbenq, Commented Apr 13, 2017 at 18:56

Kewl · Accepted Answer · 2017-04-14 07:36:58Z

3

Substring takes in starting and ending indexes, not length. The line:

str.substring(i,length-i);

is asking for a string from index i (4) to index length-i (3), not a string of the remaining length.

Take out the -i.

edited Apr 14, 2017 at 7:36

Kewl

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answered Apr 13, 2017 at 19:00

ErinPac

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1 Comment

mangusta Over a year ago

the line is asking for a string from index "i" to index "length-i" without including "length-i", in other words [i, length-i)

Vladimir Parfenov · Accepted Answer · 2017-04-13 18:46:13Z

0

You wrote:

str.substring(i,length-i);

i increase's and in one moment i will be >= length - i.

answered Apr 13, 2017 at 18:46

Vladimir Parfenov

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3 Comments

shailbenq Over a year ago

I checked this line, the values of "i" and "length" before this error is thrown is 4 and 7 respectively

Vladimir Parfenov Over a year ago

So you call str.substring(4, 7-4). Begin index = 4, end index = 3. Range = -1.

shailbenq Over a year ago

Yep the range is -1 here.

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