Example 1: new hashmap java
Map<String, String> myMap = new HashMap<String, String>() {{
put("a", "b");
put("c", "d");
}};
Example 2: java hashmap methods
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.
Example 3: java hashmap syntax
// Import the HashMap class
import java.util.HashMap;
// First Example
// 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);
//Second Example
// Create a HashMap object called stGrade
Map<String, Integer> stGrade = new HashMap<String, Integer>();
// Insert elements
stGrade.put("aaron", new Integer(90));
stGrade.put("isaac", new Integer(100));
stGrade.put("john", new Integer(35));
stGrade.put("mohammad", new Integer(100));
// Get value
stGrade.get("mohammad"); // returns 100
stGrade.get("aaron"); // returns 90
stGrade.get("john"); // returns 35
stGrade.get("isaac"); // returns 100
Example 4: java hashmap example
//Hash map creation
Map< String,Integer> hm =
new HashMap< String,Integer>();
//inserting elements into hashmap
hm.put("a", new Integer(100));
hm.put("b", new Integer(200));
hm.put("c", new Integer(300));
hm.put("d", new Integer(400));
Example 5: hashmap
- HasHMap can have null key, order is not guaranteed