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Implement new concept exercise for list and generic-types (exercism#2007)
* Begin setting up the language-list exercise * Update implementation and config Start setting up the concept documentation as well. * Finish list and generic docs Also mark both unblocked exercises as active
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‎concepts/generic-types/.meta/config.json

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{
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"blurb": "Generics types allow the compiler to enforce type restraints within a class or interface.",
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"authors": [
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"jmrunkle"
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],
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"contributors": []
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}

‎concepts/generic-types/about.md

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# About Generic Types
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A **generic type** is a generic class or interface that is parameterized over types.
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This allows the compiler to enforce type safety on the class or interface.
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Consider this non-generic `Container` interface:
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```java
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class Container {
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private Object object;
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public void set(Object object) { this.object = object; }
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public Object get() { return object; }
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}
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```
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Since it accepts and returns Object types, it works with any non-primitive type.
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However, this comes at a cost because some code may call `get` expecting `Integer`s while other code calls `set` adding `String`s resulting in a runtime exception.
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A **generic class** and **generic interface** have the following formats:
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```java
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class ClassName<T1, T2, ..., Tn> { ... }
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interface InterfaceName<T1, T2, ..., Tn> { ... }
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```
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The type parameter section, delimited by angle brackets (`<>`), following the class or interface name specifies the type parameters (also called type variables) `T1`, `T2`, ..., and `Tn`.
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These can be used inside the body of the class or interface to get generic type safety.
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Here is the generic version of `Container`:
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```java
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class Container<E> {
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private E object;
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public void set(E object) { this.object = object; }
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public E get() { return object; }
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}
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```
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When created, now we have to declare what type it holds and the compiler will enforce that constraint:
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```java
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// empty <> can infer from context
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Container<String> stringContainer = new Container<>();
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// compiler knows this is a String, so it is allowed
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stringContainer.set("Some string");
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// no cast needed, compiler knows it is a String
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String result = stringContainer.get();
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// this causes a compiler error:
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stringContainer.set(42);
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```

‎concepts/generic-types/introduction.md

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# Introduction to Generic Types
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A **generic type** is a generic class or interface that is parameterized over types.
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This allows the compiler to enforce type safety on the class or interface.
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Consider this non-generic `Container` interface:
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```java
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class Container {
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private Object object;
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public void set(Object object) { this.object = object; }
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public Object get() { return object; }
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}
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```
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Since it accepts and returns Object types, it works with any non-primitive type.
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However, this comes at a cost because some code may call `get` expecting `Integer`s while other code calls `set` adding `String`s resulting in a runtime exception.
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A **generic class** and **generic interface** have the following formats:
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```java
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class ClassName<T1, T2, ..., Tn> { ... }
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interface InterfaceName<T1, T2, ..., Tn> { ... }
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```
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The type parameter section, delimited by angle brackets (`<>`), following the class or interface name specifies the type parameters (also called type variables) `T1`, `T2`, ..., and `Tn`.
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These can be used inside the body of the class or interface to get generic type safety.
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Here is the generic version of `Container`:
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```java
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class Container<E> {
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private E object;
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public void set(E object) { this.object = object; }
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public E get() { return object; }
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}
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```
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When created, now we have to declare what type it holds and the compiler will enforce that constraint:
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```java
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// empty <> can infer from context
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Container<String> stringContainer = new Container<>();
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// compiler knows this is a String, so it is allowed
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stringContainer.set("Some string");
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// no cast needed, compiler knows it is a String
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String result = stringContainer.get();
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// this causes a compiler error:
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stringContainer.set(42);
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```

‎concepts/generic-types/links.json

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[
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{
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"url": "https://docs.oracle.com/javase/tutorial/java/generics/types.html",
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"description": "generics"
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}
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]

‎concepts/lists/.meta/config.json

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{
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"blurb": "TODO: add blurb for lists concept",
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"blurb": "Lists are an ordered collection that allows duplicates.",
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"authors": [
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"mirkoperillo"
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"jmrunkle"
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],
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"contributors": []
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}

‎concepts/lists/about.md

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# About
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# About Lists
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TODO: add information on lists concept
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**Lists** are the ordered sequence collection in Java.
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Unlike arrays, a [`List`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html) can grow in size to accomodate any number of items.
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One standard implementation is the `ArrayList` which is backed by a re-sizable array.
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Another standard implementation is the `LinkedList` class which is backed by a doubly-linked list.
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`List`s may be empty or hold any number of items (including duplicates).
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`List`s are a **generic interface** typed to indicate which type of objects they can contain.
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For example:
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```java
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List<String> emptyListOfStrings = List.of();
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List<Integer> singleInteger = List.of(1);
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List<Boolean> threeBooleans = List.of(true, false, true);
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List<Object> listWithMulitipleTypes = List.of("hello", 1, true);
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```
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`List`s have various helpful methods to add, remove, get, and check for an element to be present:
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```java
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List<Character> vowels = new ArrayList<>(List.of('a', 'e', 'i', 'o', 'i', 'e', 'a'));
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int startingSize = vowels.size(); // 7
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vowels.add('u'); // vowels is now ['a', 'e', 'i', 'o', 'i', 'e', 'a', 'u']
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char a = vowels.get(0); // 'a'
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boolean hadI = vowels.remove('i'); // true and vowels is now ['a', 'e', 'o', 'i', 'e', 'a', 'u']
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boolean hasI = vowels.contains('i'); // true (still have one more left)
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```
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The [`Collections`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Collections.html) class also has some helpful utilities for dealing with collections like `List`:
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```java
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List<Integer> numbers = new ArrayList<>(List.of(1, 5, 3, 2, 4));
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Collections.sort(numbers); // [1, 2, 3, 4, 5]
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Collections.reverse(numbers); // [5, 4, 3, 2, 1]
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Collections.fill(numbers, 42); // [42, 42, 42, 42, 42]
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List<Integer> fiveNines = Collections.nCopies(5, 9); // [9, 9, 9, 9, 9]
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```

‎concepts/lists/introduction.md

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# Introduction
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# Introduction to Lists
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TODO: add introduction for lists concept
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**Lists** are the ordered sequence collection in Java.
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Unlike arrays, a [`List`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html) can grow in size to accomodate any number of items.
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One standard implementation is the `ArrayList` which is backed by a re-sizable array.
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Another standard implementation is the `LinkedList` class which is backed by a doubly-linked list.
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`List`s may be empty or hold any number of items (including duplicates).
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`List`s are a **generic interface** typed to indicate which type of objects they can contain.
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For example:
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```java
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List<String> emptyListOfStrings = List.of();
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List<Integer> singleInteger = List.of(1);
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List<Boolean> threeBooleans = List.of(true, false, true);
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List<Object> listWithMulitipleTypes = List.of("hello", 1, true);
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```
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`List`s have various helpful methods to add, remove, get, and check for an element to be present:
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```java
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List<Character> vowels = new ArrayList<>(List.of('a', 'e', 'i', 'o', 'i', 'e', 'a'));
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int startingSize = vowels.size(); // 7
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vowels.add('u'); // vowels is now ['a', 'e', 'i', 'o', 'i', 'e', 'a', 'u']
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char a = vowels.get(0); // 'a'
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boolean hadI = vowels.remove('i'); // true and vowels is now ['a', 'e', 'o', 'i', 'e', 'a', 'u']
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boolean hasI = vowels.contains('i'); // true (still have one more left)
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```

‎concepts/lists/links.json

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[]
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[
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{
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"url": "https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html",
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"description": "javadoc"
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},
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{
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"url": "https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Collections.html",
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"description": "collections"
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}
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]

‎config.json

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],
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"status": "active"
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},
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{
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"slug": "karls-languages",
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"name": "Karl's Languages",
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"uuid": "1ad2ab97-df3e-4bc9-b0f6-e8dcc9eb10f1",
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"concepts": [
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"lists",
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"generic-types"
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],
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"prerequisites": [
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"arrays",
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"for-loops",
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"strings"
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],
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"status": "active"
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},
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{
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"slug": "squeaky-clean",
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"name": "Squeaky Clean",
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"lists",
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"strings"
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],
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"status": "wip"
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"status": "active"
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},
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{
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"slug": "cars-assemble",
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"slug": "for-loops",
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"name": "For Loops"
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},
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{
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"uuid": "7de03b7d-ed91-4699-b275-96a6ab2e441c",
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"slug": "generic-types",
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"name": "Generic Types"
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},
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{
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"uuid": "90776fcc-c6a7-4665-b5fe-5a8a0618358b",
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"slug": "inheritance",

‎exercises/concept/karls-languages/.docs/hints.md

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## 1. Define a function to check if the language list is empty
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* Try using the [`isEmpty()`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html#isEmpty()) method.
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## 2. Define a function to add a language to the list
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* Try using the [`add(E element)`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html#add(E)) method.
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* Reminder: methods that return `void` do not need any `return` statements.
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## 3. Define a function to remove a language from the list
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* Try using the [`remove(Object o)`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html#remove(java.lang.Object)) method.
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* Reminder: methods that return `void` do not need any `return` statements.
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## 4. Define a function to return the first item in the list
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* Try using the [`get(int index)`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html#get(int)) method.
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## 5. Define a function to return how many languages are in the list
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* Try using the [`size()`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html#size()) method.
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## 6. Define a function to determine if a language is in the list
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* Try using the [`contains(Object o)`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html#contains(java.lang.Object)) method.
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## 7. Define a function to determine if the list is exciting
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* Try using a [for-each loop](https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html) through all of the elements, checking each one.
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* Alternatively, try using the `containsLanguage` method from the previous step.

‎exercises/concept/karls-languages/.docs/instructions.md

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# Instructions
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Karl wants to keep track of a list of languages to learn on Exercism's website.
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Karl needs to be able to add new languages, remove old ones and check if certain languages are in the list.
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It would be very exciting if Karl wants to learn Java or Kotlin!
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## 1. Define a function to check if the language list is empty
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Karl needs to know if his list of languages ever becomes empty so he can go find more to learn!
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Define a method called `isEmpty` which returns `true` if there are no languages in the list.
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```java
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if (languageList.isEmpty()) {
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findMoreLanguagesToLearn();
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}
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```
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## 2. Define a function to add a language to the list
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Karl is looking forward to learning Kotlin and Python!
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Help Karl get started by defining a method called `addLanguage` which takes the language he wants to learn and adds it to the list.
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```java
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languageList.addLanguage("Kotlin");
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languageList.addLanguage("Python");
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```
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## 3. Define a function to remove a language from the list
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Karl decided he does not want to learn Scala right now.
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Help Karl remove it from the list by defining a method called `removeLanguage` which takes the language he is removing and removes it from the list.
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```java
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languageList.removeLanguage("Scala");
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```
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## 4. Define a function to return the first item in the list
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Karl wants to remember the first language he added to the list (that is still in the list).
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Define a method called `firstLanguage` that returns the first language in the list.
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```java
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String kotlin = languageList.firstLanguage(); // "Kotlin"
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```
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## 5. Define a function to return how many languages are in the list
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Karl needs to know how many languages he is trying to learn.
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Help Karl find the answer by defining a method called `count` which returns the number of languages in the list.
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```java
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int two = languageList.count(); // 2
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```
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## 6. Define a function to determine if a language is in the list
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Karl is trying to remember if he wanted to learn Python or Ruby.
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Define a method called `containsLanguage` which takes the language he is asking about so Karl can find out!
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```java
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boolean learningPython = languageList.containsLanguage("Python"); // true
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boolean learningRuby = languageList.containsLanguage("Ruby"); // false
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```
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## 7. Define a function to determine if the list is exciting
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If Karl wants to learn Java or Kotlin, that is very exciting!
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Define a method called `isExciting` that returns true if Karl wants to learn Java or Kotlin.
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```java
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javaLanguageList.isExciting() // true
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neitherKotlinNorJavaLanguageList.isExciting() // false
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```

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