substring index range

Code:

public class Test {
    public static void main(String[] args) {
        String str = "University";
        System.out.println(str.substring(4, 7));
    }   
}

Output: ers

I do not really understand how the substring method works. Does the index start at 0? If I start with 0, e is at index 4 but char i is at 7 so the output would be ersi.

0: U

1: n

2: i

3: v

4: e

5: r

6: s

7: i

8: t

9: y

Start index is inclusive

End index is exclusive

Javadoc link

Both are 0-based, but the start is inclusive and the end is exclusive. This ensures the resulting string is of length start - end.

To make life easier for substring operation, imagine that characters are between indexes.

0 1 2 3 4 5 6 7 8 9 10  <- available indexes for substring 
 u n i v E R S i t y
        ↑     ↑
      start  end --> range of "E R S"

Quoting the docs:

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.

See the javadoc. It's an inclusive index for the first argument and exclusive for the second.

Like you I didn't find it came naturally. I normally still have to remind myself that

• the length of the returned string is

  lastIndex - firstIndex

• that you can use the length of the string as the lastIndex even though there is no character there and trying to reference it would throw an Exception

so

"University".substring(6, 10)

returns the 4-character string "sity" even though there is no character at position 10.

public String substring(int beginIndex, int endIndex)

beginIndex—the begin index, inclusive.

endIndex—the end index, exclusive.

Example:

public class Test {

    public static void main(String args[]) {
        String Str = new String("Hello World");

        System.out.println(Str.substring(3, 8));
    }
 }

Output: "lo Wo"

From 3 to 7 index.

Also there is another kind of substring() method:

public String substring(int beginIndex)

beginIndex—the begin index, inclusive. Returns a sub string starting from beginIndex to the end of the main String.

Example:

public class Test {

    public static void main(String args[]) {
        String Str = new String("Hello World");

        System.out.println(Str.substring(3));
    }
}

Output: "lo World"

From 3 to the last index.