.subString方法无法正常工作，Java

Question

I am creating a simple program to convert binary numbers to hex, without the use of the methods provided by Java to do so. I have most of my code already, I'm just having trouble with my "split string" method.

Basically all I am trying to do in this method is

1) Take in a string (binary number)

2) Create an array of strings to hold the "groupings" of numbers

3) Split the binary number into groups of 4 digits (eg 10011101 = 1001, 1101)

4) Return the array of groupings

However, when using my method, it always only takes 3 for the first element in my "groupings" array. (eg should be "1001", but only putting "100"). What am I doing wrong here?

public String[] splitIntoFours (String toSplit) {
    int stringPart = 4;
    int arraySize = toSplit.length() / 4;
        String[] groupings = new String[arraySize];
        for (int iterator = 0; (iterator * stringPart) < toSplit.length(); iterator++){
            //If statement to deal with the inital case of the iterator being 0, 
            //where this algorithm only takes the first 3 numbers instead of a 
            //sequence of 4 numbers.

            int start = iterator * stringPart;
            int end = start + stringPart;
            if (end > toSplit.length()) {
                 end = toSplit.length();
            }
            groupings[iterator] = toSplit.substring(start, end);
        }
    return groupings;   
    }

Answer 1

Remember that substring will not return the character at the index denoted by end. It returns end-1.

The Javadoc and extract

public String substring(int beginIndex, int endIndex)

Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

Examples:

"hamburger".substring(4, 8) returns "urge"

"smiles".substring(1, 5) returns "mile"

Answer 2

String.substring中的第二个参数（endIndex）是互斥的，请仔细阅读文档中的示例。

Answer 3

Copying this code and running it, it works correctly. So there is no problem. The output, using a String.length dividable through 4, is correct.

Answer 4

Your method works fine, although it throws an error when the size of the number that has to be split is not an multiple of four. This method is a bit more generic:

public static String[] split(String str, int sizeOfGroups) {
        int arraySize = str.length() / sizeOfGroups;
        String[] groupings = new String[arraySize+1];
        int num1, num2;

        for (int i = 0; i * sizeOfGroups < str.length(); i++) {

            num1 = i * sizeOfGroups + sizeOfGroups;
            num2 = i * sizeOfGroups;

            if ((num1 >= str.length())) {
                groupings[i] = str.substring(num2, str.length());
            } else {
                groupings[i] = str.substring(num2, num1);
            }
        }

        return groupings;

    }