Add maps concept

concepts/maps/.meta/config.json

@@ -0,0 +1,7 @@
+{
+  "blurb": "Maps are a data structure that holds key-value pairs. Keys and values can be of any reference data type, and the keys must be unique.",
+  "authors": [
+    "smcg468"
+  ],
+  "contributors": []
+}

concepts/maps/about.md

@@ -0,0 +1,78 @@
+# About
+
+[Maps][maps] in Java is an interface that holds data in key-value pairs.
+
+- Keys can be of any [reference type][reference-data-types], but must be unique.
+- Values can be of any reference type, they do not have to be unique.
+
+We have three different views that can all be accessed individually
+
+- keys,
+
+```java
+Map<String, Integer> map = new HashMap<>();
+
+// Generates a set view of the keys in the hashmap
+map.keySet();
+```
+
+- values
+
+```java
+Map<String, Integer> map = new HashMap<>();
+
+// Generates a set view of the values in the hashmap
+map.values();
+```
+
+- and key-value mappings.
+
+````java
+Map<String, Integer> map = new HashMap<>();
+
+for (String key: map.keySet()) {
+    System.out.println("Key = " + key);
+    System.out.println("Value = " + map.get(key));
+}
+````
+
+## Map declaration
+
+Due to Map being an interface, it is recommended we create an object of a class that implements the map interface as shown in the example below that is creating an object of the HashMap class.
+There are many useful [built-in functions][start-of-map-functions] that allow you to modify these map objects.
+
+```java
+Map<String, Integer> hashmap = new HashMap<>();
+```
+
+In regards to the declaration of the HashMap object, the first data type specified `String` represents the data type of the key, and `Integer` represents the data type of the value in the example above.
+
+## Classes that implement Map
+
+We then have the main three classes that are used which implement the Map interface, these are [HashMap][hash-map], [LinkedHashMap][linked-hash-map] and [TreeMap][tree-map].
+Below are some key differences in the three classes.
+
+### Hashmap
+
+- Implements the Map interface.
+- No guaranteed order of the elements inserted.
+- Null values are allowed.
+
+### LinkedHashMap
+
+- Implements the Map interface.
+- Elements are in the order that they have been inserted.
+- Null values are allowed.
+
+### Treemap
+
+- Implements the Map, SortedMap and NavigableMap interfaces.
+- Elements are sorted according to the natural ordering, keys will be compared using the compareTo() method by default or keys can be compared using another comparator if specified.
+- Null values are **not** allowed.
+
+[maps]: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Map.html
+[reference-data-types]: https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.3
+[hash-map]: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html
+[linked-hash-map]: https://docs.oracle.com/javase/8/docs/api/java/util/LinkedHashMap.html
+[tree-map]: https://docs.oracle.com/javase/8/docs/api/java/util/TreeMap.html
+[start-of-map-functions]: https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#size--

concepts/maps/introduction.md

@@ -0,0 +1,52 @@
+# Introduction
+
+[Maps][maps] in Java is an interface that holds data in key-value pairs.
+
+- Keys can be of any [reference type][reference-data-types], but must be unique.
+- Values can be of any reference type, they do not have to be unique.
+
+We have three different views that can all be accessed individually
+
+- keys,
+
+```java
+Map<String, Integer> map = new HashMap<>();
+
+// Generates a set view of the keys in the hashmap
+map.keySet();
+```
+
+- values
+
+```java
+Map<String, Integer> map = new HashMap<>();
+
+// Generates a set view of the values in the hashmap
+map.values();
+```
+
+- and key-value mappings.
+
+````java
+Map<String, Integer> map = new HashMap<>();
+
+for (String key: map.keySet()) {
+    System.out.println("Key = " + key);
+    System.out.println("Value = " + map.get(key));
+}
+````
+
+## Map declaration
+
+Due to Map being an interface, it is recommended we create an object of a class that implements the map interface as shown in the example below that is creating an object of the HashMap class.
+There are many useful [built-in functions][start-of-map-functions] that allow you to modify these map objects.
+
+```java
+Map<String, Integer> hashmap = new HashMap<>();
+```
+
+In regards to the declaration of the HashMap object, the first data type specified `String` represents the data type of the key, and `Integer` represents the data type of the value in the example above.
+
+[maps]: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Map.html
+[reference-data-types]: https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.3
+[start-of-map-functions]: https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#size--

concepts/maps/links.json

@@ -0,0 +1,26 @@
+[
+  {
+    "url": "https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Map.html",
+    "description": "Detailed explanation of the map interface in Java."
+  },
+  {
+    "url": "https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.3",
+    "description": "Reference types defined in Java, reference types are the data types used for the key/value pairs."
+  },
+  {
+    "url": "https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html",
+    "description": "Detailed explanation of the HashMap class in Java."
+  },
+  {
+    "url": "https://docs.oracle.com/javase/8/docs/api/java/util/LinkedHashMap.html",
+    "description": "Detailed explanation of the LinkedHashMap class in Java."
+  },
+  {
+    "url": "https://docs.oracle.com/javase/8/docs/api/java/util/TreeMap.html",
+    "description": "Detailed explanation of the TreeMap class in Java."
+  },
+  {
+    "url": "https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#size--",
+    "description": "List of the built-in functions that can be utilised with map objects."
+  }
+]

config.json

@@ -271,6 +271,18 @@
           "numbers",
           "strings"
         ]
+      },
+      {
+        "slug": "arcade-high-score",
+        "name": "Arcade High Score",
+        "uuid": "07893a1a-eb93-4ad2-b98e-f3946c5e7fb2",
+        "concepts": [
+          "maps"
+        ],
+        "prerequisites": [
+          "numbers",
+          "strings"
+        ]
       }
     ],
     "practice": [
@@ -436,11 +448,13 @@
         "name": "Word Count",
         "uuid": "3603b770-87a5-4758-91f3-b4d1f9075bc1",
         "practices": [
-          "strings"
+          "strings",
+          "maps"
         ],
         "prerequisites": [
           "for-loops",
-          "arrays"
+          "arrays",
+          "maps"
         ],
         "difficulty": 5
       },
@@ -829,11 +843,13 @@
         "name": "Nucleotide Count",
         "uuid": "2d80fdfc-5bd7-4b67-9fbe-8ab820d89051",
         "practices": [
-          "strings"
+          "strings",
+          "maps"
         ],
         "prerequisites": [
           "if-else-statements",
-          "for-loops"
+          "for-loops",
+          "maps"
         ],
         "difficulty": 5
       },
@@ -987,10 +1003,12 @@
         "practices": [
           "if-else-statements",
           "for-loops",
-          "enums"
+          "enums",
+          "maps"
         ],
         "prerequisites": [
-          "enums"
+          "enums",
+          "maps"
         ],
         "difficulty": 7
       },
@@ -1032,12 +1050,14 @@
         "practices": [
           "arrays",
           "strings",
-          "if-else-statements"
+          "if-else-statements",
+          "maps"
         ],
         "prerequisites": [
           "arrays",
           "strings",
-          "if-else-statements"
+          "if-else-statements",
+          "maps"
         ],
         "difficulty": 7
       },
@@ -1516,13 +1536,15 @@
         "uuid": "873c05de-b5f5-4c5b-97f0-d1ede8a82832",
         "practices": [
           "for-loops",
-          "numbers"
+          "numbers",
+          "maps"
         ],
         "prerequisites": [
           "exceptions",
           "for-loops",
           "if-else-statements",
-          "numbers"
+          "numbers",
+          "maps"
         ],
         "difficulty": 8
       },
@@ -1689,10 +1711,12 @@
         "name": "Parallel Letter Frequency",
         "uuid": "38a405e8-619d-400f-b53c-2f06461fdf9d",
         "practices": [
-          "strings"
+          "strings",
+          "maps"
         ],
         "prerequisites": [
-          "strings"
+          "strings",
+          "maps"
         ],
         "difficulty": 6
       },
@@ -1981,13 +2005,16 @@
         "slug": "sgf-parsing",
         "name": "SGF Parsing",
         "uuid": "0d6325d1-c0a3-456e-9a92-cea0559e82ed",
-        "practices": [],
+        "practices": [
+          "maps"
+        ],
         "prerequisites": [
           "strings",
           "chars",
           "if-else-statements",
           "lists",
-          "for-loops"
+          "for-loops",
+          "maps"
         ],
         "difficulty": 7
       },
@@ -2191,6 +2218,11 @@
       "uuid": "78f3c7b2-cb9c-4d21-8cb4-7106a188f713",
       "slug": "ternary-operators",
       "name": "Ternary Operators"
+    },
+    {
+      "uuid": "5a10c26d-1f8a-46d3-ab85-686235000f0e",
+      "slug": "maps",
+      "name": "Maps"
     }
   ],
   "key_features": [

exercises/concept/arcade-high-score/.docs/hints.md

@@ -0,0 +1,41 @@
+# Hints
+
+## General
+
+- A [map][maps] is an associative data structure of key-value pairs.
+
+## 1. Define a new high score map
+
+- It should return an empty [map][maps].
+- [Create an object][create-object] of the HashMap class using the declared `Map<String ,Integer> highScores`.
+
+## 2. Add players to the high score map
+
+- The resulting map should be returned.
+- One of the [built-in functions][map-put] can be used to put a value in a map under a given key.
+
+## 3. Remove players from the score map
+
+- The resulting map should be returned.
+- One of the [built-in functions][map-remove] can be used to remove a key/value pair from a map.
+
+## 4. Reset a player's score
+
+- The resulting map should be returned with the player's score reset to an initial value of 0.
+- One of the [built-in functions][map-put] can be used to put a value in a map under a given key.
+
+## 5. Update a player's score
+
+- The resulting map should be returned with the player's updated score.
+- One of the [built-in functions][map-get-or-default] can be used to get a value in a map under a given key if the key is present and update the value, or add the key with a default value if it is not present..
+
+## 6. Get a list of players
+
+- One of the [built-in functions][map-keys] returns a set of all keys in a map.
+
+[maps]: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Map.html
+[create-object]: https://docs.oracle.com/javase/tutorial/java/javaOO/objectcreation.html
+[map-put]: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#put-K-V-
+[map-remove]: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#remove-java.lang.Object-
+[map-get-or-default]: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#getOrDefault-java.lang.Object-V-
+[map-keys]: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#keySet--