# Unit 3 Write Code Practice for Classes

Each coding exercise has its own folder. Open its `.java` file and press **Run** to try it. **Run Tests** checks every graded exercise in this lesson at once.

After doing the [mixed-up code problems](https://runestone.academy/ns/books/published/csawesome2/classes-parsons.html) on CS Awesome, try doing similar write code problems below.

## Exercise 1

Fix the code so that the `Dog` class has a constructor that takes in a String argument `name` and assigns that value to the instance variable `name`.

> Open the `01-u3-muc-wc1` folder and edit `Dog.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 2

Create a constructor for the `Dog` class that takes two parameters, `name` (a String) and `age` (an integer), and saves them in the correspondingly-named instance variables.

> Open the `02-u3-muc-wc2` folder and edit `Dog.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 3

Fix the errors (commented as “TODO”) in the code so that it defines the `Cat` class correctly. There should be a `makeSound` method that prints `"meow"` and returns nothing. There should also be a `toString` method that returns `"Name: name, Age: age"` (such that `Cat("Lucky", 10)`’s `toString` method would return `"Name: Lucky, Age: 10"`).

> Open the `03-u3-muc-wc3` folder and edit `Cat.java`. Press **Run** to try it; **Run Tests** checks it (4 tests).

## Exercise 4

Write code that completes the `Square` class. It needs two variables: `length` and `numberOfSquares`. `length` is an instance variable, while `numberOfSquares` is a class variable that tracks how many squares have been made. `getArea()` also needs to be completed, which will return the area of the square. Finally, there needs to be a completed `toString()` method that returns `"Length: length"` (such that `Square(5)`’s toString method would return `"Length: 5"`).

> Open the `04-u3-muc-wc4` folder and edit `Square.java`. Press **Run** to try it; **Run Tests** checks it (3 tests).

## Exercise 5

Write code that completes the `Rectangle` class. It should have constructors that can take zero or two integer parameters. With zero arguments passed, the `Rectangle` should be initialized with a `length` of 10 and a `width` of 10. With two integers passed, the `Rectangle` should have a `length` equal to the first argument and a `width` equal to the second argument. There should also be a `getArea` method that returns the area `length` times `width`.

> Open the `05-u3-muc-wc5` folder and edit `Rectangle.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 6

Write code that completes the `CelestialBody` class. Each `CelestialBody` instance has an integer `orbitLength` (in days) and a integer `daysSinceDiscovered` attribute (which is initially 0). Using these, write the `orbit(int numberOfTimes)` method that adds `numberOfTimes * orbitLength` to `daysSinceDiscovered` (e.g., if Planet X has done two orbits with an orbit length of 12 days, it was discovered 24 days ago. If it then orbits another three times, it was discovered 60 days ago). Also, fix the two errors in the class.

> Open the `06-u3-muc-wc6` folder and edit `CelestialBody.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 7

Write code to create a `Person` class. Each `Person` instance should have a String `name` attribute and a integer `age` attribute. There should also be `getName` and `setName` methods. Finally, there should to be a `toString` method that returns “{name} is {age} years old” (e.g., `Person("Carol", 12)`’s toString method would return `"Carol is 12 years old"`).

> Open the `07-u3-muc-wc7` folder and edit `Person.java`. Press **Run** to try it; **Run Tests** checks it (3 tests).

## Exercise 8

Write code to create a `Point` class. Each `Point` instance should have integer `x` and `y` attributes (and the constructor should take those in that order). There should be getter methods for each: `getX` and `getY`. There should be a `getDistance` method that takes in another `Point` object as an argument and calculates the euclidean distance from this object to that one (which would be sqrt((this.x - other.x) ^ 2 + (this.y - other.y) ^ 2)). Finally, there should to be a `toString` method that returns “(Point.x, Point.y)” (e.g., `Point(3, 4)`’s toString method would return `"(3, 4)"`).

> Open the `08-u3-muc-wc8` folder and edit `Point.java`. Press **Run** to try it; **Run Tests** checks it (4 tests).

## Exercise 9

Write code to create an `Account` class. Each `Account` instance should have integer `balance` and String `owner` attributes (and the constructor should take those in that order). To increase `balance`, there should be a `deposit` method that takes in an integer argument and adds that to `balance`. To decrease `balance`, there should be a `withdraw` method that takes in an integer argument and subtracts that from `balance`. However, if `balance` would end as a negative number, it should just be set to zero. Finally, there should be a `toString` method that returns `"Account.owner: $Account.balance"` (so for `Account(5, "Tom")` it should return `"Tom: $5"`).

> Open the `09-u3-muc-wc9` folder and edit `Account.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 10

Write code that completes the `Character` class. Each `Character` instance has an integer `healthPoints` (abbreviated HP) attribute and a String `name` attribute. They also have the associated `getHP`, `setHP`, and `getName` methods. Using these, write code that finishes the `fight(Character other)` method that lets a character fight another. If the character’s `healthPoints` are the same or more than `other`’s, `other`’s HP should be set to zero, the current character’s HP should be set to the difference, and the program should print “{the character’s name} wins”. That entire section is already completed. On the other hand, if `other`’s HP is greater, the current character’s HP should be set to zero, `other`’s HP should be set to the difference, and the program should print “{other’s name} wins”.

> Open the `10-u3-muc-wc10` folder and edit `Character.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).