if (!isValid()) throw new IllegalStateException("accessing top or bottom frame");
if (!isValid()) throw new DataflowAnalysisException("accessing top or bottom frame");
	public ValueType getTopValue() throws DataflowAnalysisException {		if (!isValid()) throw new IllegalStateException("accessing top or bottom frame");		assert slotList.size() >= numLocals;		if (slotList.size() == numLocals)			throw new DataflowAnalysisException("operand stack is empty");		return slotList.get(slotList.size() - 1);	}