Java

We have written the following Gradebook interface: interface Gradebook { public double getAverage(); TASK: Create a class called SimpleGradebook that has the following properties: It must implement the Gradebook interface It should have a private ArrayList instance variable grades to store the grades It must have a public no-parameter constructor that initializes grades to an empty ArrayList It must have a public instance method addGrade that has one double parameter grade and a return type of boolean. If grade is valid (i.e., 0 s grade s 100), it should add grade to the grades instance variable and return true; otherwise, it should just return false and do nothing else It must have a public no-parameter instance method getAverage that returns the average of the grades in the grades member variable as a double