@Override
	public void setInputStream(IntStream input) {
		this._input = null;
		this._tokenFactorySourcePair = new Pair<TokenSource, CharStream>(this, _input);
		reset();
		this._input = (CharStream)input;
		this._tokenFactorySourcePair = new Pair<TokenSource, CharStream>(this, _input);
	}
Set the char stream and reset the lexer
runtime/Java/src/org/antlr/v4/runtime/Lexer.java