Associative Array

Author: Deepak Malik

README.md

@@ -36,7 +36,7 @@ Below topics/problems are covered as of now.
 **2. Arrays**
 - [X] [Arrays Introduction](../master/src/com/deepak/data/structures/Arrays/Arrays_Introduction.md)
 - [X] [Basic operations on Arrays](../master/src/com/deepak/data/structures/Arrays/BasicOperations.java)
-- [ ] Associative Array
+- [X] [Associative Array](../master/src/com/deepak/data/structures/Arrays/AssociativeArray.java)
 - [ ] Sparse Array
 - [ ] Tuple
 - [X] [ArrayList Implementation](../master/src/com/deepak/data/structures/Arrays/CustomArrayList.java)

src/com/deepak/data/structures/Arrays/AssociativeArray.java

@@ -0,0 +1,171 @@
+/**
+ * Data-Structures-In-Java
+ * AssociativeArray.java
+ */
+package com.deepak.data.structures.Arrays;
+
+/**
+ * Associative Arrays in Java :
+ * 
+ * Associative arrays are data structure, where keys are associated with some sort
+ * of values. Though java does not support associative arrays, but same functionality
+ * can be achieved through HashMap or HashTable. 
+ * Below is the replica of HashMap just names as associative arrays.
+ * 
+ * @author Deepak
+ */
+public class AssociativeArray<K, V> {
+
+	/* Table to hold key value pairs */
+	private Entry<K, V>[] table;
+
+	/* Variable to hold size of the map */
+	private int size;
+
+	/* Default table size */
+	private static final int DEFAULT_TABLE_SIZE = 10;
+
+	/**
+	 * Constructor
+	 */
+	public AssociativeArray() {
+		this(DEFAULT_TABLE_SIZE);
+	}
+
+	/**
+	 * Constructor
+	 * 
+	 * @param size
+	 */
+	@SuppressWarnings("unchecked")
+	public AssociativeArray(int size) {
+		this.table = new Entry[size];
+		this.size = 0;
+	}
+
+	/**
+	 * Method to add/update a entry
+	 * 
+	 * @param key
+	 * @param value
+	 */
+	public void put(K key, V value) {
+		boolean isNewEntry = true;
+		/* Find the hash of the key and bucket it belongs to */
+		int hash = key.hashCode();
+		int bucket = getBucket(hash);
+		/* Loop through each entry of the associative array 
+		 * and check if it's just a value update or a new key, value */
+		for (Entry<K, V> entry : table) {
+			if (entry != null && entry.getKey().equals(key)) {
+				entry.value = value;
+				isNewEntry = false;
+			}
+		}
+		/* Create a new entry and push to array */
+		if (isNewEntry) {
+			Entry<K, V> newEntry = new Entry<>(key, value, hash);
+			newEntry.next = table[bucket];
+			table[bucket] = newEntry;
+			size++;
+		}
+	}
+
+	/**
+	 * Method to find the value for a given key
+	 * 
+	 * @param key
+	 * @return {@link V}
+	 */
+	public V get(K key) {
+		/* Find hash code and bucket associated with key */
+		int hash = key.hashCode();
+		int bucket = getBucket(hash);
+		/* Get all the entries on that column of bucket */
+		Entry<K, V> entry = table[bucket];
+		while (entry != null) {
+			/* If hash and key matches, return the value */
+			if (entry.getHash() == hash && entry.getKey() == key) {
+				return entry.getValue();
+			}
+			entry = entry.next;
+		}
+		return null;
+	}
+
+	/**
+	 * Method to get size of associative array
+	 * 
+	 * @return {@link int}
+	 */
+	public int size() {
+		return size;
+	}
+
+	/**
+	 * Method to check if associative array is empty 
+	 * 
+	 * @return {@link boolean}
+	 */
+	public boolean isEmpty() {
+		return size == 0;
+	}
+
+	/**
+	 * Method to get bucket based on the hash
+	 * 
+	 * @param hash
+	 * @return {@link int}
+	 */
+	private int getBucket(int hash) {
+		return (hash % table.length);
+	}
+
+	/**
+	 * Static class Entry for associative array
+	 * 
+	 * @author Deepak
+	 *
+	 * @param <K>
+	 * @param <V>
+	 */
+	public static class Entry<K, V> {
+
+		/* Variables for key, value, hash and next entry */
+		private final K key;
+		private V value;
+		private Entry<K, V> next;
+		private int hash;
+
+		/**
+		 * Constructor
+		 * 
+		 * @param key
+		 * @param value
+		 * @param hash
+		 */
+		public Entry(K key, V value, int hash) {
+			this.key = key;
+			this.value = value;
+			this.hash = hash;
+		}
+
+		public Entry<K, V> getNext() {
+			return next;
+		}
+
+		public K getKey() {
+			return key;
+		}
+
+		public V getValue() {
+			return value;
+		}
+
+		public int getHash() {
+			return hash;
+		}
+
+	}
+
+}

src/com/deepak/data/structures/Arrays/BasicOperations.java

@@ -1,5 +1,6 @@
 /**
- * Data-Structures-in-Java
+ * Data-Structures-In-Java
+ * BasicOperations.java
  */
 package com.deepak.data.structures.Arrays;
 
@@ -146,7 +147,6 @@ public static void main(String[] args) {
 		int[] z = new int[x.length];
 		System.arraycopy(x, 0, z, 0, x.length);
 		System.out.println("Using System.ArrayCopy() method to copy original array " + Arrays.toString(x) + " to new one => " + Arrays.toString(z));
-
 	}
 
 }

src/com/deepak/data/structures/Arrays/CustomArrayList.java

@@ -1,5 +1,5 @@
 /**
- * Data-Structures-in-Java
+ * Data-Structures-In-Java
  * CustomArrayList.java
  */
 package com.deepak.data.structures.Arrays;

test/com/deepak/data/structures/Arrays/ArrayListTest.java

@@ -1,5 +1,5 @@
 /**
- * Data-Structures-in-Java
+ * Data-Structures-In-Java
  * ArrayListTest.java
  */
 package com.deepak.data.structures.Arrays;

test/com/deepak/data/structures/Arrays/AssociativeArrayTest.java

@@ -0,0 +1,48 @@
+/**
+ * Data-Structures-In-Java
+ * AssociativeArrayTest.java
+ */
+package com.deepak.data.structures.Arrays;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * Test cases for associative array
+ * 
+ * @author Deepak
+ */
+public class AssociativeArrayTest {
+
+	/* Associative array defined */
+	AssociativeArray<String, String> associativeArray;
+
+	/**
+	 * Method to setup associative array
+	 */
+	@Before
+	public void setup() {
+		associativeArray = new AssociativeArray<>(3);
+		associativeArray.put("A", "Apple");
+		associativeArray.put("B", "Ball");
+		associativeArray.put("C", "Cat");
+		associativeArray.put("D", "Dog");
+		associativeArray.put("E", "Elephant");
+		associativeArray.put("F", "Fan");
+		associativeArray.put("G", "Goat");
+	}
+
+	/**
+	 * Method to test associative Array
+	 */
+	@Test
+	public void testAssociativeArray() {
+		Assert.assertEquals(associativeArray.size(), 7);
+		Assert.assertFalse(associativeArray.isEmpty());
+		Assert.assertEquals(associativeArray.get("D"), "Dog");
+		associativeArray.put("D", "Dice");
+		Assert.assertEquals(associativeArray.get("D"), "Dice");
+	}
+
+}