Create and work with interfaces In this exercise, you'll create the DepartmentConstants interface presented in this chapter. In addition, you'll implement an interface named Displayable that similar to the Printable interface presented in this chapter. Create the interfaces 1. Open the project named ch09_exl_Displayable Test in the ex starts folder. Then, review the code.
2. Note that this code includes an interface named Displayable that contains a single method named getDisplay Text() that returns a String.
3. Open the Displayable TestApp class. Then, note that it includes a method named display that accepts a Displayable object as an argument.
4 Add an interface named Department Constants that contains these three constants: ADMIN, EDITORIAL, and MARKETING. Implement the interfaces
5. Open the Product class. Then, edit it so it implements the Displayable interface. To do that, add a getDisplay Text() method that returns a description of the product.
6. Open the Employee class. Then, edit it so it implements the DepartmentConstants and Displayable interfaces. To do that, add a getDisplay Text() method that uses the constants in the Department Constants interface to include the department name and the employee's name in the string that it returns. Use the classes that implement the interfaces
7. Open the Displayable TestApp class. Then, modify the variable that stores the Employee object so it is of the Displayable type.
8. Add code that passes the Displayable object to the static display method that's coded at the end of this class.
9. Run the application to make sure that it displays the employee information.
10. Repeat the previous three steps for a Product object. When you're done, the console should look like this: Welcome to the Displayable Test application John Smith (Editorial) Murach's Java Programming Use a default method
11. In the Employee and Product classes, rename the getDisplay Text() methods to toString() methods so they override the toString method of the Object class. This should prevent the classes from compiling and display an error message that indicates that the classes don't implement the getDisplay Text() method. Section 2 Object-oriented programming
12. In the Displayable interface, modify the getDisplay Text() method so it's a default method. The code for this method should return the String object that's returned by the toString() method. This should allow the Employeee and Product classes to compile since they can now use the default method
13. Run the application to make sure it works as before.