java hashmap methods
// Import the HashMap class
import java.util.HashMap;
// Create a HashMap object called capitalCities
HashMap<String, String> capitalCities = new HashMap<String, String>();
// Add keys and values (Country, City)
capitalCities.put("England", "London");
capitalCities.put("Germany", "Berlin");
capitalCities.put("Norway", "Oslo");
capitalCities.put("USA", "Washington DC");
System.out.println(capitalCities);
import java.util.HashMap; // import the HashMap class
// instantiate a HashMap instance
HashMap<String, String> capitalCities = new HashMap<String, String>();
// SCROLL DOWN FOR LIST OF ALL METHODS --------------------------------------
// to use any methods below add the function name to the instance name
// General Form: HashMapInstanceName.{functionName}({parameter list});
// Specific Example Using the Put Method:
capitalCities.put("California", "Sacramento");
// SCROLL DOWN FOR LIST OF ALL METHODS --------------------------------------
1. void clear()
- Removes all of the mappings from this map.
2. Object clone()
- Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.
3. boolean containsKey(Object key)
- Returns true if this map contains a mapping for the specified key.
4. boolean containsValue(Object value)
- Returns true if this map maps one or more keys to the specified value.
5. V get(Object key)
- Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
6. V getOrDefault(Object key, V defaultValue)
- Returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.
7. boolean isEmpty()
- Returns true if this map contains no key-value mappings.
8. Set<K> keySet()
- Returns a Set view of the keys contained in this map.
9. V put(K key, V value)
- Associates the specified value with the specified key in this map.
10. V remove(Object key)
- Removes the mapping for the specified key from this map if present.
11. boolean remove(Object key, Object value)
- Removes the entry for the specified key only if it is currently mapped to the specified value.
12. V replace(K key, V value)
- Replaces the entry for the specified key only if it is currently mapped to some value.
13. boolean replace(K key, V oldValue, V newValue)
- Replaces the entry for the specified key only if currently mapped to the specified value.
14. int size()
- Returns the number of key-value mappings in this map.
15. Collection<V> values()
- Returns a Collection view of the values contained in this map.
// Java code to illustrate the put() method
import java.util.*;
public class Hash_Map_Demo {
public static void main(String[] args)
{
// Creating an empty HashMap
HashMap<Integer, String> hash_map = new HashMap<Integer, String>();
// Mapping string values to int keys
hash_map.put(10, "Geeks");
hash_map.put(15, "4");
hash_map.put(20, "Geeks");
hash_map.put(25, "Welcomes");
hash_map.put(30, "You");
// Displaying the HashMap
System.out.println("Initial Mappings are: " + hash_map);
// Inserting existing key along with new value
String returned_value = (String)hash_map.put(20, "All");
// Verifying the returned value
System.out.println("Returned value is: " + returned_value);
// Displayin the new map
System.out.println("New map is: " + hash_map);
}
}