Concept explainers
MyMap using Open Addressing with Linear Probing
Program Plan:
- Define a class named “Sample” to implement MyMap using open addressing with linear probing.
- Define function main.
- Define an integer HashMap named “map”.
- Put ‘2, 2” into the map.
- Remove “2” from the map.
- Define a static class named “MyHashMap” and implement “MyMap”.
- Define required variables.
- Define a function named “MyHashMap”.
- Construct a map with the default capacity and load factor.
- Define a function named “MyHashMap” with one parameter.
- Construct a map with the specific initial capacity and default load factor.
- Define a function named “MyHashMap” with two parameters.
- Construct a map with the default capacity and load factor.
- Define a function named “clear”.
- Remove all of the entries from this map.
- Define a function named “containsKey”.
- Return true if the specified key is in the map.
- Define a function named “containsValue”.
- Return true if this map contains the specific value.
- Define a function named “entrySet”.
- Return a set of entries in the map.
- Define a function named “get”.
- Return the first value that matches the specific key.
- Define a function named “getAll”.
- Return all values for the specified key in this map.
- Define a function named “isEmpty”.
- Return true if this map contains no entries.
- Define a function named “keyset”.
- Return a set consisting of the keys in this map.
- Define a function named “put”.
- Add an entry (key, value) into the map and return the value.
- Define a function named “remove”.
- Remove the element for the specific key.
- Define a function named “size”.
- Return the number of mappings in this map.
- Define a function named “values”.
- Return a set consisting of the values in this map.
- Define a function named “hash”.
- Return “hashCode % capacity” value.
- Define a function named “supplmentHash”.
- Ensure the hashing is evenly distributed and return the result.
- Define a function named “removeEntries”.
- Remove all entries from each bucket.
- Define a function named “rehash”.
- Rehash this map.
- Define a function named “toString”.
- Return a string representing for this map.
- Define an interface name “MyMap”.
- Declare function prototypes for the functions which are created at the class “MyHashMap”.
- Define function main.
The below program creates a new concrete class that implements MyMap using open addressing with linear probing, whose hash table size is 4 and the table size get doubled when the load factor exceeds the threshold 0.5.
Explanation of Solution
Program:
public class Sample {
/** Main method */
public static void main(String[] args) {
MyHashMap<Integer, Integer> map = new MyHashMap<>();
map.put(2, 2);
System.out.println("Is key 2 in the map? " + map.containsKey(2));
map.remove(2);
System.out.println("Is key 2 in the map? " + map.containsKey(2));
}
static class MyHashMap<K, V> implements MyMap<K, V> {
// Define the default hash table size.
private static int INITIAL_CAPACITY = 4;
// Define the maximum hash table size. 1 << 30 is same as 2^30
private static int MAX_CAPACITY = 1 << 30;
// Current hash table capacity.
private int capacity;
// Define default load factor
private static float MAX_LOAD_FACTOR = 0.5f;
// Specify a load factor used in the hash table
private float loadFactorThreshold;
// The number of entries in the map
private int size = 0;
// Hash table is an array with each cell that is a linked list
MyMap.Entry<K, V>[] table;
/** Construct a map with the default capacity and load factor */
public MyHashMap() {
this(INITIAL_CAPACITY, MAX_LOAD_FACTOR);
}
/**
* Construct a map with the specified initial capacity and default load
* factor
*/
public MyHashMap(int initialCapacity) {
this(initialCapacity, MAX_LOAD_FACTOR);
}
/**
* Construct a map with the specified initial capacity and load factor
*/
public MyHashMap(int initialCapacity, float loadFactorThreshold) {
this.capacity = initialCapacity;
this.loadFactorThreshold = loadFactorThreshold;
table = new MyMap.Entry[capacity];
}
/** Remove all of the entries from this map */
public void clear() {
size = 0;
removeEntries();
}
/** Return true if the specified key is in the map */
public boolean containsKey(K key) {
if (get(key) != null)
return true;
else
return false;
}
/** Return true if this map contains the specified value */
public boolean containsValue(V value) {
for (int i = 0; i < table.length; i++)
if (table[i] != null && table[i].value.equals(value))
return true;
return false;
}
/** Return a set of entries in the map */
public java.util.Set<MyMap.Entry<K, V>> entrySet() {
java.util.Set<MyMap.Entry<K, V>> set = new java.util.HashSet<MyMap.Entry<K, V>>();
for (int i = 0; i < capacity; i++)
if (table[i] != null)
set.add(table[i]);
return set;
}
/** Return the first value that matches the specified key */
public V get(K key) {
// Perform linear probing
int i = hash(key.hashCode());
while (table[i] != null) {
if (table[i].key != null && table[i].key.equals(key))
return table[i].value;
i = (i + 1) % table.length;
}
return null;
}
/** Return all values for the specified key in this map */
public java.util.Set<V> getAll(K key) {
java.util.Set<V> set = new java.util.HashSet<V>();
for (int i = 0; i < capacity; i++)
if (table[i] != null && table[i].key.equals(key))
set.add(table[i].value);
return set;
}
/** Return true if this map contains no entries */
public boolean isEmpty() {
return size == 0;
}
/** Return a set consisting of the keys in this map */
public java.util.Set<K> keySet() {
java.util.Set<K> set = new java.util.HashSet<K>();
for (int i = 0; i < capacity; i++)
if (table[i] != null)
set.add(table[i].key);
return set;
}
/** Add an entry (key, value) into the map */
public V put(K key, V value) {
if (size >= capacity * loadFactorThreshold) {
if (capacity == MAX_CAPACITY)
throw new RuntimeException("Exceeding maximum capacity");
rehash();
}
int i = hash(key.hashCode());
while (table[i] != null && table[i].key != null)
i = (i + 1) % table.length;
// Add an entry (key, value) to the table
table[i] = new MyMap.Entry<K, V>(key, value);
size++; // Increase size
return value;
}
/** Remove the element for the specified key */
public void remove(K key) {
int i = hash(key.hashCode());
while (table[i] != null
&& (table[i].key == null || !table[i].key.equals(key)))
i = (i + 1) % table.length;
if (table[i] != null && table[i].key.equals(key)) {
// A special marker Entry(null, null) is placed for the deleted
// entry
table[i] = new MyMap.Entry<K, V>(null, null);
size--;
}
}
/** Return the number of mappings in this map */
public int size() {
return size;
}
/** Return a set consisting of the values in this map */
public java.util.Set<V> values() {
java.util.Set<V> set = new java.util.HashSet<V>();
for (int i = 0; i < capacity; i++)
if (table[i] != null)
set.add(table[i].value);
return set;
}
/** Hash function */
private int hash(int hashCode) {
return hashCode % capacity;
// return supplementHash(hashCode) & (capacity - 1);
}
/** Ensure the hashing is evenly distributed */
private static int supplementHash(int h) {
h ^= (h >>> 20) ^ (h >>> 12);
return h ^ (h >>> 7) ^ (h >>> 4);
}
/** Remove all entries from each bucket */
private void removeEntries() {
for (int i = 0; i < capacity; i++)
table[i] = null;
}
/** Rehash the map */
private void rehash() {
java.util.Set<Entry<K, V>> set = entrySet(); // Get entries
capacity <<= 1; // Double capacity
table = new Entry[capacity]; // Create a new hash table
size = 0; // Clear size
for (Entry<K, V> entry : set) {
put(entry.getKey(), entry.getValue()); // Store to new table
}
}
@Override
/** Return a string representation for this map */
public String toString() {
StringBuilder builder = new StringBuilder("[");
for (int i = 0; i < capacity; i++) {
if (table[i] != null && table[i].key != null)
builder.append(table[i].toString());
}
return builder.append("]").toString();
}
}
interface MyMap<K, V> {
/** Remove all of the entries from this map */
public void clear();
/** Return true if the specified key is in the map */
public boolean containsKey(K key);
/** Return true if this map contains the specified value */
public boolean containsValue(V value);
/** Return a set of entries in the map */
public java.util.Set<Entry<K, V>> entrySet();
/** Return the first value that matches the specified key */
public V get(K key);
/** Return all values for the specified key in this map */
public java.util.Set<V> getAll(K key);
/** Return true if this map contains no entries */
public boolean isEmpty();
/** Return a set consisting of the keys in this map */
public java.util.Set<K> keySet();
/** Add an entry (key, value) into the map */
public V put(K key, V value);
/** Remove the entries for the specified key */
public void remove(K key);
/** Return the number of mappings in this map */
public int size();
/** Return a set consisting of the values in this map */
public java.util.Set<V> values();
/** Define inner class for Entry */
public static class Entry<K, V> {
K key;
V value;
public Entry(K key, V value) {
this.key = key;
this.value = value;
}
public K getKey() {
return key;
}
public V getValue() {
return value;
}
@Override
public String toString() {
return "[" + key + ", " + value + "]";
}
}
}
}
Is key 2 in the map? true
Is key 2 in the map? false
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Chapter 27 Solutions
Introduction to Java Programming and Data Structures, Comprehensive Version (11th Edition)
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