// Term Tokenizer takes original expression and converts it to ArrayList of tokens
private void termTokenizer() {
// contains final list of tokens
this.tokens = new ArrayList<>();
int start = 0; // term split starting index
StringBuilder multiCharTerm = new StringBuilder(); // term holder
for (int i = 0; i < this.expression.length(); i++) {
Character c = this.expression.charAt(i);
if ( isOperator(c.toString() ) || isSeperator(c.toString()) ) {
// 1st check for working term and add if it exists
if (multiCharTerm.length() > 0) {
tokens.add(this.expression.substring(start, i));
}
// Add operator or parenthesis term to list
if (c != ' ') {
tokens.add(c.toString());
}
// Get ready for next term
start = i + 1;
multiCharTerm = new StringBuilder();
} else {
// multi character terms: numbers, functions, perhaps non-supported elements
// Add next character to working term
multiCharTerm.append(c);
}
}
// Add last term
if (multiCharTerm.length() > 0) {
tokens.add(this.expression.substring(start));
}
}
// Takes tokens and converts to Reverse Polish Notation (RPN), this is one where the operator follows its operands.
private void tokensToReversePolishNotation () {
// contains final list of tokens in RPN
this.reverse_polish = new ArrayList<>();
// stack is used to reorder for appropriate grouping and precedence
Stack tokenStack = new Stack();
for (String token : tokens) {
switch (token) {
// If left bracket push token on to stack
case "(":
tokenStack.push(token);
break;
case ")":
while (tokenStack.peek() != null && !tokenStack.peek().equals("("))
{
reverse_polish.add( (String)tokenStack.pop() );
}
tokenStack.pop();
break;
case "+":
case "-":
case "*":
case "/":
case "%":
// While stack
// not empty AND stack top element
// and is an operator
while (tokenStack.peek() != null && isOperator((String) tokenStack.peek()))
{
if ( isPrecedent(token, (String) tokenStack.peek() )) {
reverse_polish.add((String)tokenStack.pop());
continue;
}
break;
}
// Push the new operator on the stack
tokenStack.push(token);
break;
default: // Default should be a number, there could be test here
this.reverse_polish.add(token);
}
}
// Empty remaining tokens
while (tokenStack.peek() != null) {
reverse_polish.add((String)tokenStack.pop());
}
}
// Takes RPN and produces a final result
private void rpnToResult()
{
// Stack used to hold calculation while process RPN
Stack calculation = new Stack();
for (int i = 0; i < reverse_polish.size(); i++) // for loop to process RPN
{
// If the token is a number
if (!(isOperator(reverse_polish.get(i)))) {
// Push number to stack
calculation.push(reverse_polish.get(i));
} else {
double firstPop = Double.valueOf(calculation.pop().toString());
double secondPop = Double.valueOf(calculation.pop().toString());
// Pop the two top entries
// Based off of Token operator calculate result
if (reverse_polish.get(i).equals("%")) {
result = secondPop % firstPop;
} else if (reverse_polish.get(i).equals("^")) {
result = Math.pow(secondPop, firstPop);
} else if (reverse_polish.get(i).equals("*")) {
result = secondPop * firstPop;
} else if (reverse_polish.get(i).equals("/")) {
result = secondPop / firstPop;
} else if (reverse_polish.get(i).equals("+")) {
result = secondPop + firstPop;
} else if (reverse_polish.get(i).equals("-")) {
result = secondPop - firstPop;
}
// Push result back onto the stack
calculation.push(result);
}
}
// Pop final result and set as final result for expression
this.result = (double)calculation.pop();
}
For this segment, we had to write a method that would calculate the result from an array of numbers in RPN format. I was able to fulfill this task by using a for loop. Numbers are pushed to a stack, and calculations are made based on the order of the array. If statements are used to make the calculations and return them to the stack.
| Replit | Review Ticket |
|---|---|
| Replit | Review Ticket |