This test case demonstrates that CharBuffer.charAt throws IndexOutOfBoundsException for indexes that should be well within the buffer.

import java.nio.*;
import java.nio.charset.*;

public class Test
{
    public static void main(String[] args) throws Exception {
        char[] someChars = new char[5];
        for (int i=0; i<5; i++)
            someChars[i] = (char)(97 + i);
        CharBuffer cb = CharBuffer.wrap(someChars);
        char c = cb.charAt(1);
    }
}