3. a) Identify all differences between the HashMap structure and the ArrayList structure [10 marks] b) In what circumstances will random numbers generated using the Random class (e.g., using the nextInt method) appear to be completely non-random? [10 marks] c) What rules must be adhered to when adding comments to a Java program, in order to obtain meaningful 'javadoc' output? [10 marks] d) What is the 'this' keyword used for in Java? Describe two situations in which it is necessary to make use of this keyword. [10 marks] e) How are static variables and methods created in Java? What happens if a non-static method of a class tries to access a static variable of that class? What happens to the static variables of a class once the class has no instances? [10 marks]