HashMap example in Java

The HashMap class uses a hash table to implement the Map interface. This allows the execution time of basic operations, such as get() and put(), to remain constant even for large sets.
The following constructors are defined: HashMap( )
HashMap(Map m)
HashMap(int capacity)
HashMap(int capacity, float fillRatio)
The first form constructs a default hash map. The second form initializes the hash map by using the elements of m. The third form initializes the capacity of the hash map to capacity. The fourth form initializes both the capacity and fill ratio of the hash map by using its arguments. The meaning of capacity and fill ratio is the same as for HashSet, described earlier.
HashMap implements Map and extends AbstractMap. It does not add any methods of its own. You should note that a hash map does not guarantee the order of its elements. Therefore, the order in which elements are added to a hash map is not necessarily the order in which they are read by an iterator.
The following program illustrates HashMap. It maps names to account balances. Notice how a set-view is obtained and used.
 


import java.util.*;
class HashMapDemo {
public static void main(String args[]) {
// Create a hash map
HashMap hm = new HashMap();
// Put elements to the map
hm.put("Raj", new Double(3434.34));
hm.put("Arun", new Double(123.22));
hm.put("Avi", new Double(1378.00));
hm.put("Paresh", new Double(99.22));
hm.put("Jonan", new Double(-19.08));
// Get a set of the entries
Set set = hm.entrySet();
// Get an iterator
Iterator i = set.iterator();
// Display elements
while(i.hasNext()) {
Map.Entry me = (Map.Entry)i.next();
System.out.print(me.getKey() + ": ");
System.out.println(me.getValue());
}
System.out.println();
// Deposit 1000 into John Doe's account
double balance = ((Double)hm.get("John Doe")).doubleValue();
hm.put("Raj", new Double(balance + 1000));
System.out.println("Raj's new balance: " +
hm.get("Raj"));
}
}

Output from this program is shown here:
Raj: -19.08 
Arun: 123.22
Avi: 3434.34
Paresh: 99.22 
Jonan: 1378.0
Raj's current balance: 4434.34