HashMap uses the hash table to implement the Map interface. Map is key-value pair where key is the reference and value is the actual data. HashMap is very extensively used in the projects when key-value type data is stored. This doesn’t ensure the order of insertion. This class extends the AbstractMap and implements the Map interface.
HaspMap supports the four types of constructors:
- HashMap( )
- HashMap(Map m)
- HashMap(int capacity)
- HashMap(int capacity, float fillRatio)
HashMap Methods
- void clear() –> Clears all entries in this map.
- Object clone() –> Returns a clone of the map object
- boolean containsKey(Object key) –> Will return true if the map contains the key
- boolean containsValue(Object value) –> Will return true if this map maps one or more keys to the specified value.
- Set entrySet() –> Will return true if a collection of the mappings found this map.
- Object get(Object key) –> Will return the value to which the passed key is mapped in this identity hash map, or null if the map contains no mapping for the passed key.
- boolean isEmpty() –> Will return true if this map contains no entries
- Set keySet() –> Will return the set of keys in the map object
- Object put(Object key, Object value) –> Will link the key and value passed
- putAll(Map m) –> Copy all of the amppings to the another map
- Object remove(Object key) –> Will remove the passed key-value from the map
- int size() –> Will return the size of the map
- Collection values() –> Will retrun the collection view of the map values. It may be a list of values
HashMap Example
package javabeat.net.core; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Map.Entry; import java.util.Set; public class HashMapExample { public static void main(String args[]) { // Create a default hash map HashMap<String,String> hashmap = new HashMap<String,String>(); // Add elements to the map hashmap.put("1", "Entry 1"); hashmap.put("2", "Entry 2"); hashmap.put("3", "Entry 3"); // Get a set of the entries Set<Entry<String, String>> set = hashmap.entrySet(); // Get an iterator Iterator<Entry<String, String>> i = set.iterator(); // Display elements while (i.hasNext()) { Map.Entry<String,String> mapEntry = i.next(); System.out.print(mapEntry.getKey() + ": "); System.out.println(mapEntry.getValue()); } } }
The output for the above example will be:
3: Entry 3 2: Entry 2 1: Entry 1