@Override
	public Token get(int i) { // get absolute index
		int bufferStartIndex = getBufferStartIndex();
		if (i < bufferStartIndex || i >= bufferStartIndex + n) {
			throw new IndexOutOfBoundsException("get("+i+") outside buffer: "+
			                    bufferStartIndex+".."+(bufferStartIndex+n));
		}
		return tokens[i - bufferStartIndex];
	}
Absolute token index. It's the index of the token about to be read via
{@code LT(1)}. Goes from 0 to the number of tokens in the entire stream,
although the stream size is unknown before the end is reached.

<p>This value is used to set the token indexes if the stream provides tokens
that implement {@link WritableToken}.</p>
runtime/Java/src/org/antlr/v4/runtime/UnbufferedTokenStream.java