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classes - new exercise
* classes initial commit * classes initial commit * classes code * classes proofing * classes proofing classes - addressed review points * classes - address missed review point * classes updated config.sys etc.
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‎exercises/concept/classes/.docs/after.md‎

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The primary object-oriented construct in Java is the _class_, which is a combination of data ([_fields_][fields]), also known as instance variables, and behavior ([_methods_][methods]). The fields and methods of a class are known as its _members_.
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Access to members can be controlled through access modifiers, the two most common ones being:
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- [`public`][public]: the member can be accessed by any code (no restrictions).
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- [`private`][private]: the member can only be accessed by code in the same class.
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In Java if no access modifier is specified, the default is _package visibility_. In this case, the member is visible to all classes defined into the same package.
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The above-mentioned grouping of related data and behavior plus restricting access to members is known as [_encapsulation_][encapsulation], which is one of the core object-oriented concepts.
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You can think of a class as a template for creating instances of that class. To [create an instance of a class][creating-objects] (also known as an _object_), the [`new` keyword][new] is used:
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```java
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class Car {
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}
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// Create two car instances
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Car myCar = new Car();
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Car yourCar = new Car();
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```
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[Fields][fields] have a type and a name (cased in [camelCase][camel-case]) and can be defined anywhere in a class (cased in [PascalCase][pascal-case]).
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```java
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class Car {
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// Accessible by anyone
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public int weight;
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// Only accessible by code in this class
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private String color;
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}
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```
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One can optionally assign an initial value to a field. If a field does _not_ specify an initial value, it will be set to its type's [default value][default-values]. An instance's field values can be accessed and updated using dot-notation.
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```java
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class Car {
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// Will be set to specified value
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public int weight = 2500;
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// Will be set to default value (0)
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public int year;
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}
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Car newCar = new Car();
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newCar.weight; // => 2500
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newCar.year; // => 0
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// Update value of the field
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newCar.year = 2018;
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```
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Private fields are usually updated as a side effect of calling a method. Such methods usually don't return any value, in which case the return type should be [`void`][void]:
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```java
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class CarImporter {
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private int carsImported;
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public void ImportCars(int numberOfCars)
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{
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// Update private field
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carsImported = carsImported + numberOfCars;
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}
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}
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```
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Note that is not customary to use public fields in Java classes. Private fields are typically used which are accessed through [_getters_ and _setters_][so-getters-setters].
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Within a class, the [`this` keyword][this] will refer to the current class. This is especially useful if a parameter has the same name as a field:
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```java
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class CarImporter {
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private int carsImported;
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public void SetImportedCars(int carsImported)
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{
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// Update private field from public method
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this.carsImported = carsImported;
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}
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}
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```
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[fields]: https://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html
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[methods]: https://docs.oracle.com/javase/tutorial/java/javaOO/methods.html
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[this]: https://docs.oracle.com/javase/tutorial/java/javaOO/thiskey.html
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[new]: https://docs.oracle.com/javase/tutorial/java/javaOO/objectcreation.html
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[void]: https://en.wikibooks.org/wiki/Java_Programming/Keywords/void
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[creating-objects]: https://docs.oracle.com/javase/tutorial/java/javaOO/objectcreation.html
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[public]: https://en.wikibooks.org/wiki/Java_Programming/Keywords/public
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[private]: https://en.wikibooks.org/wiki/Java_Programming/Keywords/private
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[default-values]: https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html
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[camel-case]: https://techterms.com/definition/camelcase
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[pascal-case]: https://techterms.com/definition/pascalcase
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[encapsulation]: https://en.wikipedia.org/wiki/Encapsulation_(computer_programming)
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[so-getters-setters]: https://stackoverflow.com/questions/2036970/how-do-getters-and-setters-work

‎exercises/concept/classes/.docs/hints.md‎

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## General
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## 1. Buy a brand-new remote controlled car
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- [This page shows how to create a new instance of a class][creating-objects].
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## 2. Display the distance driven
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- Keep track of the distance driven in a [field][fields].
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- Consider what visibility to use for the field (does it need to be used outside the class?).
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## 3. Display the battery percentage
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- Keep track of the distance driven in a [field][fields].
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- Initialize the field to a specific value to correspond to the initial battery charge.
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- Consider what visibility to use for the field (does it need to be used outside the class?).
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## 4. Update the number of meters driven when driving
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- Update the field representing the distance driven.
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## 5. Update the battery percentage when driving
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- Update the field representing the battery percentage driven.
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## 6. Prevent driving when the battery is drained
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- Add a conditional to only update the distance and battery if the battery is not already drained.
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- Add a conditional to display the empty battery message if the battery is drained.
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[creating-objects]: https://docs.oracle.com/javase/tutorial/java/javaOO/objectcreation.html
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[fields]: https://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html

‎exercises/concept/classes/.docs/instructions.md‎

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In this exercise you'll be playing around with a remote controlled car, which you've finally saved enough money for to buy.
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Cars start with full (100%) batteries. Each time you drive the car using the remote control, it covers 20 meters and drains one percent of the battery.
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The remote controlled car has a fancy LED display that shows two bits of information:
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- The total distance it has driven, displayed as: `"Driven <METERS> meters"`.
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- The remaining battery charge, displayed as: `"Battery at <PERCENTAGE>%"`.
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If the battery is at 0%, you can't drive the car anymore and the battery display will show `"Battery empty"`.
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You have six tasks, each of which will work with remote controlled car instances.
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## 1. Buy a brand-new remote controlled car
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Implement the (_static_) `RemoteControlCar.buy()` method to return a brand-new remote controlled car instance:
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```java
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RemoteControlCar car = RemoteControlCar.buy();
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```
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## 2. Display the distance driven
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Implement the `RemoteControlCar.distanceDisplay()` method to return the distance as displayed on the LED display:
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```java
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RemoteControlCar car = RemoteControlCar.buy();
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car.distanceDisplay();
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// => "Driven 0 meters"
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```
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## 3. Display the battery percentage
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Implement the `RemoteControlCar.batteryDisplay()` method to return the distance as displayed on the LED display:
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```java
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RemoteControlCar car = RemoteControlCar.buy();
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car.batteryDisplay();
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// => "Battery at 100%"
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```
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## 4. Update the number of meters driven when driving
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Implement the `RemoteControlCar.drive()` method that updates the number of meters driven:
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```java
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RemoteControlCar car = RemoteControlCar.buy();
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car.drive();
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car.drive();
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car.distanceDisplay();
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// => "Driven 40 meters"
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```
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## 5. Update the battery percentage when driving
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Update the `RemoteControlCar.drive()` method to update the battery percentage:
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```java
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RemoteControlCar car = RemoteControlCar.buy();
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car.drive();
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car.drive();
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car.batteryDisplay();
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// => "Battery at 98%"
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```
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## 6. Prevent driving when the battery is drained
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Update the `RemoteControlCar.drive()` method to not increase the distance driven nor decrease the battery percentage when the battery is drained (at 0%):
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```java
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RemoteControlCar car = RemoteControlCar.buy();
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// Drain the battery
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// ...
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car.distanceDisplay();
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// => "Driven 2000 meters"
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car.batteryDisplay();
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// => "Battery empty"
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```

‎exercises/concept/classes/.docs/introduction.md‎

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The primary object-oriented construct in Java is the _class_, which is a combination of data (_fields_) and behavior (_methods_). The fields and methods of a class are known as its _members_.
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Access to members can be controlled through access modifiers, the two most common ones being:
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- `public`: the member can be accessed by any code (no restrictions).
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- `private`: the member can only be accessed by code in the same class.
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You can think of a class as a template for creating instances of that class. To create an instance of a class (also known as an _object_), the `new` keyword is used:
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```java
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class Car {
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}
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// Create two car instances
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Car myCar = new Car();
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Car yourCar = new Car();
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```
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Fields have a type and a name (defined in camelCase) and can be defined anywhere in a class (by convention cased in PascalCase):
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```java
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class Car {
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// Accessible by anyone
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public int weight;
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// Only accessible by code in this class
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private String color;
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}
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```
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One can optionally assign an initial value to a field. If a field does _not_ specify an initial value, it wll be set to its type's default value. An instance's field values can be accessed and updated using dot-notation.
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```java
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class Car {
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// Will be set to specified value
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public int weight = 2500;
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// Will be set to default value (0)
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public int year;
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}
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Car newCar = new Car();
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newCar.weight; // => 2500
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newCar.year; // => 0
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// Update value of the field
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newCar.year = 2018;
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```
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Private fields are usually updated as a side effect of calling a method. Such methods usually don't return any value, in which case the return type should be `void`:
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```java
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class CarImporter {
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private int carsImported;
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public void ImportCars(int numberOfCars)
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{
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// Update private field from public method
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carsImported = carsImported + numberOfCars;
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}
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}
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```

‎exercises/concept/classes/.meta/config.json‎

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{
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"contributors": [
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{
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"github_username": "mirkoperillo",
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"exercism_username": "mirkoperillo"
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}
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],
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"authors": [
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{
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"github_username": "mikedamay",
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"exercism_username": "mikedamay"
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}
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]
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}

‎exercises/concept/classes/.meta/design.md‎

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## Learning objectives
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- Know what classes are.
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- Know what encapsulation is.
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- Know what fields are.
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- Know how to create an object.
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- Know how to update state through methods.
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- Know about the `void` type.
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## Out of scope
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- Reference equality.
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- Constructors.
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- Interfaces.
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- Inheritance.
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- Finalizers.
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- Method overloading.
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## Concepts
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- `classes`: know what classes are; know what encapsulation is; know what fields are; know how to create an object; know how to update state through methods; know about the `void` type.
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## Prerequisites
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- `basics`: know how to define a basic class with basic methods.
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- `strings`: know how to do basic string interpolation.
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- `numbers`: know how to compare numbers.
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- `conditionals`: know how to do conditional logic.

‎exercises/concept/classes/.meta/src/reference/java/RemoteControlCar.java‎

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class RemoteControlCar {
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private int batteryPercentage = 100;
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private int distanceDrivenInMeters = 0;
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public void drive() {
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if (batteryPercentage > 0) {
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batteryPercentage--;
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distanceDrivenInMeters += 20;
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}
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}
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public String distanceDisplay() {
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return "Driven " + distanceDrivenInMeters + " meters";
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}
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public String batteryDisplay() {
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if (batteryPercentage == 0) {
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return "Battery empty";
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}
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return "Battery at " + batteryPercentage + "%";
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}
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public static RemoteControlCar buy() {
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return new RemoteControlCar();
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}
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}

‎exercises/concept/classes/build.gradle‎

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apply plugin: "java"
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apply plugin: "eclipse"
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apply plugin: "idea"
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repositories {
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mavenCentral()
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}
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dependencies {
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testCompile "junit:junit:4.13"
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testImplementation "org.assertj:assertj-core:3.15.0"
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}
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test {
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testLogging {
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exceptionFormat = 'short'
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showStandardStreams = true
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events = ["passed", "failed", "skipped"]
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}
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}

‎exercises/concept/classes/src/main/java/RemoteControlCar.java‎

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public class RemoteControlCar {
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public static RemoteControlCar buy() {
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throw new UnsupportedOperationException("Please implement the (static) RemoteControlCar.buy() method");
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}
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public String distanceDisplay() {
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throw new UnsupportedOperationException("Please implement the (static) RemoteControlCar.distanceDisplay() method");
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}
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public String batteryDisplay() {
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throw new UnsupportedOperationException("Please implement the (static) RemoteControlCar.batteryDisplay() method");
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}
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public void drive() {
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throw new UnsupportedOperationException("Please implement the (static) RemoteControlCar.drive() method");
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}
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}

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