Fix

Author: Hardvan

src/main/java/com/thealgorithms/stacks/PostfixEvaluator.java

@@ -41,10 +41,24 @@ public static int evaluatePostfix(String expression) {
         return stack.pop();
     }
 
+    /**
+     * Checks if the given token is an operator.
+     *
+     * @param token The token to check.
+     * @return true if the token is an operator, false otherwise.
+     */
     private static boolean isOperator(String token) {
         return token.equals("+") || token.equals("-") || token.equals("*") || token.equals("/");
     }
 
+    /**
+     * Applies the given operator to the two operands.
+     *
+     * @param operator The operator to apply.
+     * @param a The first operand.
+     * @param b The second operand.
+     * @return The result of applying the operator to the operands.
+     */
     private static int applyOperator(String operator, int a, int b) {
         return switch (operator) {
             case "+" -> a + b;