Creating a Hash Map in java

This example shows how to create hash map and perform some operations on it.

// Create a hash table 
Map map = new HashMap();   // hash table
//Map map = new TreeMap(); // you can do sorted 
//map as well


// Add key/value pairs to the map 
map.put("a", new Integer(1));
map.put("b", new Integer(2));
map.put("c", new Integer(3));


// Get number of entries in map 
int size = map.size(); // 2

// Adding an entry whose key exists in the map causes 

// the new value to replace the old value 
Object oldValue = map.put("a", new Integer(9)); // 1


// Remove an entry from the map and return the value of the removed entry 
oldValue = map.remove("c"); // 3


// Iterate over the keys in the map 
Iterator it = map.keySet().iterator();
while (it.hasNext()) {
// Get key
    Object key = it.next();
} // Iterate over the values in the map
it = map.values().iterator();
while (it.hasNext()) {
    // Get value
     Object value = it.next();
}