Java and for the test cases junit 4

1. This problem concerns a class TelephoneMemory, which models the telephone system responsible for saved numbers. Specifically it can store saved numbers 0 through 9. The class has the following methods: A constructor that creates a memory whose only saved number is number 1, which starts with the value "123-4357" (123-HELP). This is the customer service number for the company selling the phone. (Note that we're representing the phone numbers as strings. This system always uses strings: just assume that all strings entered into the system are valid.) A method set that takes an integer and a string. It will make that string the new value for the saved number identified by the integer. For example, set(3, "123-4567") will sct saved number 3 to "123-4567". The integer must be in the range 0-9 or the method will throw an IndexOutOfBoundsException. The method should return whether that saved number had been previously sct. A method dial that takes an integer and returns the value of that saved number. If the value given is invalid (either not in the range 0 9 or not set), then the method will throw a NoSuchElementException. Based on this description, complete the following (a) (6 points) Write a "stub" version of PhoneMemory. It should be a class with this name that has methods matching these descriptions and that compiles, but with minimal code to compile. (No effort needs to be made to properly implement the functionality.) (b) (20 points) Write JUnit test cases for PhoneMemory. All properties of the class should be thoroughly tested