private void evaluateStack() {
if (stack.isNull()) throw new IllegalArgumentException("stack");
Stack thisStack = stack;
int total = 0;
while (thisStack != null) {
String val = thisStack.pop();
if (val.equals("+")) {
String int1 = thisStack.pop();
String int2 = thisStack.pop();
total = Integer.parseInt(int1) + Integer.parseInt(int2);
thisStack.push(Integer.toString(total));
} else if (val.equals("s")) {
String int1 = thisStack.pop();
String int2 = thisStack.pop();
thisStack.push(int1);
thisStack.push(int2);
}
}
}
private void displayStack() {
if (stack.isNull()) throw new IllegalArgumentException();
Stack thisStack = stack;
while (thisStack != null) {
System.out.println(thisStack.peek());
thisStack = thisStack.tail();
}
}
