Practical Coding in Java

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Coding Exercises: Classes and Objects

Person

Write a Person class that includes the following:

• private member variables for the name of the person (String) and the number of pets they have (int)
• public constructor taking name and number of pets as input
• public accessor functions for name and number of pets
• public member function greeting that returns a String: “Hello, my name is (name) and I have (numberOfPets) pets.”

Also write a PersonTest class that instantiates some Person objects and demonstrates that the functions are working properly.

ScoreKeeper

Write a ScoreKeeper class that includes the following:

• private member variable to keep track of the score (initialized to 0)
• public accessor function for the score
• public method scoreNormal() that adds 100 to the score
• public method scoreBonus() that adds 1000 to the score

Write a ScoreKeeperTest class that instantiates a ScoreKeeper object and tests its functions.

Magic Eight Ball

Write a MagicEightBall class that includes the following:

• private final String member variables to hold the possible replies
• public member function ask() that takes a single string as input, ignores it, and returns a string randomly from the possible replies

Write a MagicEightBallTest class that instantiates a MagicEightBall object and asks it some important questions.

Rectangle

Write a Rectangle class that includes the following:

• private double member variables for base and height
• public constructor with base and height as inputs
• public accessor functions for base and height
• public member function to return the area of the rectangle
• public member function to return the perimeter of the rectangle
• public member function to return the length of a diagonal of the rectangle

Be sure to include a test class to demonstrate that your Rectangle class functions all work properly.

Bonus Challenge: Vector

Write a Vector class that represents a two-dimensional vector \(\vec{v} = \left<x, y\right>\). Include the following:

• private double member variables for \(x\) and \(y\)

• public constructor taking \(x\) and \(y\) as input

• public accessor functions for \(x\) and \(y\)

• public member function that returns the magnitude of the vector

• public member function that returns the direction of the vector (Note: this is a little tricky in general because you need to use atan() and check the quadrant. Fortunately, the Java Math class includes a convenient function atan2(y, x) that does this check for you. Note that y comes before x.)

• public member function that adds another vector to this one (like +=):

  public void add(Vector u)

• public member function that multiplies this vector by a scalar (like *=):

  public void scalarMultiply(double k)

• public member function that computes and returns the dot product of this vector with another vector:

  public double dotProduct(Vector u)

• public member function that calculates the angle between this and another vector:

  public double angle(Vector u)

  Hint: Use what you know from pre-calculus, together with Math.acos() and the dotProduct() and magnitude() functions.

Make sure to write a test class to verify that your functions are all doing what you expect.

Next: 5. Arrays