Added JavaDoc to calculate() pure function

src/main/java/edu/unl/cse/csce361/calculator/Calculator.java

@@ -74,6 +74,23 @@ public class Calculator {
         return calculate(type, token, this.stack, this.stackPointer);
     }
 
+    /**
+     * <p>The core logic of the prefix calculator, using injected dependencies. The behavior is identical to
+     * {@link #calculate(int, char[])} except that the {@code stack} array and the {@code stackPointer} value are
+     * method parameters and not object fields.</p>
+     *
+     * <p>The {@code stackPointer} parameter indicates the top of the stack; its value is the number of items in the
+     * logical stack. Note that the {@code stack} parameter may include values that are not part of the stack. The
+     * logical stack are the values in {@code stack[0..stackPointer-1]}; the values in
+     * {@code stack[stackPointer..length-1]} are not part of the stack, and no guarantees are made about their
+     * values.</p>
+     *
+     * @param type         the type of token received from the user
+     * @param token        the token received from the user
+     * @param stack        an array representing the calculator's stack
+     * @param stackPointer the value indicating the top of the stack
+     * @return the message to be displayed to the user, or {@code Null} if no message is to be displayed
+     */
     String calculate(int type, char[] token, double[] stack, AtomicInteger stackPointer) {
         double number1;
         double number2;
@@ -173,7 +190,8 @@ public class Calculator {
     /**
      * Extracts the next whitespace-delimited token from the user input and determines its type.
      *
-     * @param token a non-{@code Null} character array in which to place the token; any existing contents will be overwritten
+     * @param token a non-{@code Null} character array in which to place the token; any existing contents will be
+     *              overwritten
      * @param limit the maximum allowable length of the token
      * @return the type of token
      * @throws IOException if there is a problem with processing the user's input (see