Please read Sections 6.3 through 6.10 and Section 6.12 of the text, and then do the following exercises.

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1 Homework #8 Quiz 28 October 2016 CS1440 P. Johann Please read Sections 6.3 through 6.10 and Section 6.12 of the text, and then do the following exercises. Part I This part of the assignment consists of review exercises intended to help you discover and remedy any misconceptions about the course material that you may have, and thus to ensure your mastery of the basics of programming in general, and Java programming in particular.you need not hand in your solutions to the review exercises, but you will be asked to write your solutions to a small number of them in a brief in-class quiz on 28 October. 1. Recall the Rectangle class from Code Listing 6-9 (pages 345 and 346) of the text. Write a method that takes a Rectangle object as its argument and displays that object s length and width fields to the terminal. 2. Recall the Rectangle class from Code Listing 6-9 (pages 345 and 346) of the text. Write a method that returns a reference to a Rectangle object. The method should prompt the user for values for the Rectangle object s length and width fields, and then actually store the values input by the user in the object s length and width fields, all before returning the reference. 3. Describe the difference in the way variables of primitive data types and class objects are passed as arguments to methods. 4. Write a class that has three overloaded static methods for calculating the areas of the following geometric shapes: circles (area = π radius 2 ) rectangles (area = length width) trapedoids (area = 1 2 (shortlength + longlength) height) Because the three methods are to be overloaded, they should all have the same name but different signatures. 5. If you do not write an equals method for a class, Java provides one. Describe the behavior of the equals method that Java automatically provides. 6. Add a copy constructor to the InventoryItem class from Code Listing 6-11 (pages 348 to 350) of the text. This constructor should take as its argument an InventoryItem object. It should assign to the description field of the object being constructed the value in the argument s description field, and assign to the units field of the object being constructed the value in the argument s units field. As a result, the newly constructed object will be a copy of the argument object. 7. Consider the following class definition: public class Circle private double radius; private double getarea()

2 return Math.PI * radius * radius; private double getradius() return radius; a) Write a no-arg constructor for this class. It should assign the radius field the value 0. b) Write an overloaded constructor for this class. It should take as its argument a value to be stored in the radius field. c) Write a tostring method for this class. The method should return a string containing the radius and the area of the circle. d) Write an equals method for this class. The method should take as its argument a Circle object. It should return true if the argument object contains the same data as the calling object, and it should return false otherwise. e) Write a greaterthan method for this class. The method should take as its argument a Circle object. It should return true if the argument object has an area greater than the area of the calling object, and it should return false otherwise. 8. Consider the following class declaration: public class Thing private int x; private int y; private static int z = 0; public Thing() x = z; y = z; public static void putthing(int a) z = a; Suppose a program containing the above class definition defines three Thing objects with the following statements: Thing one = new Thing(); Thing two = new Thing(); Thing three = new Thing(); a) How many separate instances of the x member variable exist? b) How many separate instances of the y member variable exist?

3 c) How many separate instances of the z member variable exist? d) What values will be stored in the x and y member variables of each object? e) Write a statement that will call the putthing method. 9. What is the purpose of the this keyword? 10. Describe the difference in the way variables of primitive data types and class objects are passed as arguments to methods. 11. What happens if you attempt to call a method using a reference variable that is set to null? 12. Suppose we have the following enum declaration: enum Color RED, ORANGE, GREEN, BLUE a) What is the name of the data type declared by this statement? b) What are the enum constants for this type? c) Write a statement that defines a variable of this type and initializes it with a valid value. 13. A coffee shop sells light, medium, dark, and decaf coffee beans. Write a declaration for an enumerated data type called Coffee that can represent the types of coffee the shop sells. 14. Referring back to Problem 5, find the error(s) in the following switch statement: Coffee mycup = DARK; switch (mycup) case Coffee.MEDIUM: System.out.println("Mild flavor."); case Coffee.DARK: System.out.println("Strong flavor."); case Coffee.DECAF: System.out.println("Won t keep you awake."); default: System.out.prinln("Never heard of it."); 15. Suppose we have the following enum declaration: enum Dog POODLE, BOXER, TERRIER What will the following statements display? a) System.out.println(Dog.POODLE + "\n" + Dog.BOXER + "\n" + Dog.TERRIER); b) System.out.println(Dog.POODLE.ordinal() + "\n"

4 + Dog.BOXER.ordinal() + "\n" + Dog.TERRIER.ordinal()); c) Dog mydog = Dog.BOXER; if (mydog.compareto(dog.terrier) > 0) System.out.println(myDog + " is greater than " + Dog.TERRIER); else System.out.println(myDog + " is NOT greater than " + Dog.TERRIER); Part II This part of the assignment consists of programming exercises intended to help you gain hands-on experience with programming in Java. My advice is to try to write the programs by hand, without the aid of BlueJ or any other Java compiler. When you think your programs are correct, type them into BlueJ and see if you can get them to compile the first time you try. This will provide good practice and preparation for in-class exams, on which you will be asked to write Java programs by hand. 1. Add the following to the Month class you wrote in Homework 7: a tostring method that returns the same value as the getmonthname method. an equals method that takes a Month object as an argument. If the calling object holds the same data as the calling object, then the equals method should return true. Otherwise it should return false. an greaterthan method that takes a Month object as an argument. If the calling object s monthnumber field is greater than the argument s monthnumber field, then the greaterthan method should return true. Otherwise it should return false. an lessthan method that takes a Month object as an argument. If the calling object s monthnumber field is less than the argument s monthnumber field, then the lessthan method should return true. Otherwise it should return false. 2. Design a Geometry class with the following methods: A static method that takes the radius of a circle as its argument and returns the area of the circle. (Hint: Use Math.PI for π.) A static method that takes the length and width of a rectangle as its arguments and returns the area of the rectangle. A static method that takes the base and height of a triangle as its arguments and returns the area of the triangle. (Hint: The area of a triangle is computed as 1 2 base height.) The above methods should display error messages if negative values are passed as their arguments. Next, write a program to test your Geometry class. It should display the following menu and respond to the user s selection:

5 Welcome to the Geometry Calculator! 1. Calculate the area of a circle from its radius. 2. Calculate the area of a rectange from its length and width. 3. Calculuate the area of a triangle from its base and height. 4. Quit. Enter the number of your selection (1-4): Display an error message if the user enters a number outside of the range of 1-4 when selecting an item from the menu.