Implementing MoveToFrontList The Calculator.java file contains a partially implemented class. Your job is to complete it. To get you started, the skeleton code contains method signatures for all of the methods that you must implement. Look through the code, and consider: what instance variables will you need to support your work? Hint, use an array of double values for your stack. how will you process the string expression? Here, you'll likely want to make use of the Scanner class that we used earlier. A Scanner instance can be created by passing a String as an argument to the Scanner constructor. The 'Scanner' then has several valuable methods that let us process the String and extract tokens from it. Specifically, the following methods will be useful to you ________. - hasNext() returns true iff there is another token in the input (here the input is a String); - hasNextDouble() returns true iff the next token can be turned into a double (i.e., the next token is a valid number); - next() retrieve the next token as a String; - nextDouble() return the next token and attempt to turn it into a double. Note that if the next token is actually