Collections tests added.

README.md

@@ -31,4 +31,4 @@ Following issues are introduced step by step at each commit. Please use the link
   - List concept and its application classes are in the [Arrays & Lists Package](/src/com/bilgeadam/java/tutorials/collections/arrays_lists/). (Test classes are under [here](/test/com/bilgeadam/java/tutorials/collections/arrays_lists/)) (New keywords: `Array`, `List`, `LinkedList` and `ArrayList`)
   - Queue concept and its application classes are in the [Queues Package](/src/com/bilgeadam/java/tutorials/collections/queues/). (Test classes are under [here](/test/com/bilgeadam/java/tutorials/collections/queues/)) (New keywords: `Queue`, `ArrayQueue`, `PriorityQueue` and `Stack`)
   - Set concept and its application classes are in the [Sets Package](/src/com/bilgeadam/java/tutorials/collections/sets/). (Test classes are under [here](/test/com/bilgeadam/java/tutorials/collections/sets/)) (New keywords: `Set`, `HashSet`, and `TreeSet`)
-
+  - Collections real world example cases can be found [here](/src/com/bilgeadam/java/examples/). 

src/com/bilgeadam/java/examples/recursive/MathematicalExpressionParser.java

@@ -89,18 +89,13 @@ private String consumeBucket(Stack<String> currentStack){
      * @return the result
      */
     private float parseSimpleExpression(float operandOne, float operandTwo, char operator){
-        switch (operator){
-            case '+':
-                return operandOne + operandTwo;
-            case '-':
-                return operandOne - operandTwo;
-            case '*':
-                return operandOne * operandTwo;
-            case '/':
-                return operandOne / operandTwo;
-            default:
-                throw new IllegalArgumentException("Unknown symbol: " + operator);
-        }
+        return switch (operator) {
+            case '+' -> operandOne + operandTwo;
+            case '-' -> operandOne - operandTwo;
+            case '*' -> operandOne * operandTwo;
+            case '/' -> operandOne / operandTwo;
+            default -> throw new IllegalArgumentException("Unknown symbol: " + operator);
+        };
     }
     /**
      * This method verifies given string is a {@link Double} number or not