Stacks finished data/programs/questions

other/Stacks/src/PostFix.java

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+//© A+ Computer Science  -  www.apluscompsci.com
+//Name - Ryan Walters
+//Date - 11 December 2020
+//Class - Computer Science II PreAP
+//Lab  - Lab 13C (PostFix.java)
+
+import java.util.Stack;
+import java.util.Scanner;
+
+import static java.lang.System.*;
+
+public class PostFix {
+    private Stack<Double> stack;
+    private String expression;
+
+    public PostFix() {
+        expression = "";
+        stack = new Stack<Double>();
+    }
+
+    public PostFix(String exp) {
+        expression = exp;
+    }
+
+    public void setExpression(String exp) {
+        expression = exp;
+    }
+
+    public double calc(double one, double two, char op) {
+        switch (op) {
+            case '+':
+                return one + two;
+            case '-':
+                return one - two;
+            case '*':
+                return one * two;
+            case '/':
+                return one / two;
+        }
+        return 0.0;
+    }
+
+    public void solve() {
+        stack = new Stack<Double>();
+        for (char next : expression.replace(" ", "").toCharArray()) {
+            if (isOperator(next)) {
+                double second = stack.pop();
+                double first = stack.pop();
+                stack.push(calc(first, second, next));
+            } else {
+                stack.push((double) Integer.parseInt(String.valueOf(next)));
+            }
+        }
+    }
+
+    private boolean isOperator(char op) {
+        return op == '+' || op == '-' || op == '*' || op == '/';
+    }
+
+    @Override
+    public String toString() {
+        return expression + " = " + stack.peek();
+    }
+}