String getChars() method confusion

Question

I am reading from K&B about Strings. For some extra know how, i was reading tutorial from Oracle. I am copying the source code from Oracle.

public class StringDemo {  
    public static void main(String[] args) {  
        String palindrome = "Dot saw I was Tod";  
        int len = palindrome.length();  
        char[] tempCharArray = new char[len];  
        char[] charArray = new char[len];  

        // put original string in an   
        // array of chars  
        for (int i = 0; i < len; i++) {  
            tempCharArray[i] =   
                palindrome.charAt(i);  
        }   

        // reverse array of chars  
        for (int j = 0; j < len; j++) {  
            charArray[j] =  
                tempCharArray[len - 1 - j];  
        }  

        String reversePalindrome =  
            new String(charArray);  
        System.out.println(reversePalindrome);  

        //Testing getChars method //1  
        palindrome.getChars(0, len, tempCharArray, 1);  
        String tempString = new String(tempCharArray);  
        System.out.println(tempString);  
    }  
}

I added point-1 in source code. I was understaning getChars method. When i run it, this program give me ArrayIndexOutOfBoundsException. Here is what i read in String docs.

public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)

Throws: IndexOutOfBoundsException - If any of the following is true: srcBegin is negative. srcBegin is greater than srcEnd srcEnd is greater than the length of this string dstBegin is negative dstBegin+(srcEnd-srcBegin) is larger than dst.length

What is the destBegin? What offset, the documentation is talking about. 1 is a valid offset in destination array. Please help me solve this confusion.

Thanks.

Can you add to your question the source and destination strings? That might help us clarify why it's going out of bounds. — Jason D, Sep 22 '14 at 17:31

score 1 · Answer 1 · answered Sep 22 '14 at 17:32

You get an IndexOutOfBoundsException because you have run out of room in the destination array tempCharArray, which is of length len. To copy the array, have getChars start in the destination array at the beginning of the array, at index 0.

palindrome.getChars(0, len, tempCharArray, 0);

score 1 · Accepted Answer · answered Sep 22 '14 at 17:35

1

As written in the documentation

the characters are copied into the subarray of dst starting at index dstBegin and ending at index:
 dstbegin + (srcEnd-srcBegin) - 1

so in you case is

1 + (len - 0) -1 = len

note that this is the end Index - so your end index is len but in your array the last index is len -1

answered Sep 22 '14 at 17:35

Mzf

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it means that, length of destination is automatically calculated at runtime using the formula dstbegin + (srcEnd-srcBegin) - 1, by the JVM itself. Is that true? – benz Sep 22 '14 at 17:36
why does it matter when he calculated it ? maybe it doesn't care and just simply try to write – Mzf Sep 22 '14 at 17:39

score 0 · Answer 3 · answered Sep 22 '14 at 17:34

0

tempCHarArray is of same length as that of palindrome. You are trying to copy the palindrome array starting at index 1. Try this and rerun or start index at 0 ->

char[] tempCharArray = new char[len + 1];

answered Sep 22 '14 at 17:34

dganesh2002

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String getChars() method confusion

3 Answers3