public Object getNext() {
// getNext() gets the next item on stack, pointed to by the stackPointer:
// - if stack is empty, it gets a token from Lexer and returns it, setting SP = 1
// **(in this case, the newly returned element is put on stack)
// - if SP is pointing to an existing element of stack, that element is returned, setting
// SP=SP+1
//
// - if SP is pointing right above stack, a new token from Lexer is returned, setting SP=SP+1
// **(in this case, the newly returned element is put on stack)
//
// if SP points to something that is way above stack, it returns an EOFToken().
if (stack.size() == 0) {
// System.out.println("I read " + lexer.peekNextToken());
if (lexer.hasMoreTokens()) {
stack.add(lexer.getNextToken());
stackPointer++;
return stack.get(stackPointer - 1);
} else return new EOFToken();
} else if (stackPointer < stack.size()) {
return stack.get(stackPointer++);
} else if (stackPointer == stack.size()) // execute this case only if
// stackpointer points to element right on top of stack, i.e. asks for a new element
{
if (lexer.hasMoreTokens()) {
stack.add(lexer.getNextToken());
return stack.get(stackPointer++);
} else return new EOFToken();
} else { // execute this case if stackpointer is point somewhere absurdly above the top of stack
if (diag2)
System.out.println(
"**Diag warning: invalid stack ref: getNext(), SP="
+ stackPointer
+ " for a stack of size "
+ stack.size());
return new EOFToken();
}
}
