Java Map Interface
The Map interface maps keys to values. Values can be retrieved using their corresponding keys.
- Given a key and a value, you can store the value in a Map object. After that, you can retrieve the value using its key.
- When the value being accessed does not exist, a NoSuchElementException is thrown.
- When the object type is incompatible with the element types in the Map, a ClassCastException is thrown.
- When a null object is used in a Map that does not allow null objects, a NullPointerException is thrown.
- When attempting to modify a read-only Map, an UnsupportedOperationException is thrown.
Number | Method Description |
---|---|
1 | void clear() <br>Removes all mappings from this map (optional operation). |
2 | boolean containsKey(Object k) <br>Returns true if this map contains a mapping for the specified key. |
3 | boolean containsValue(Object v) <br>Returns true if this map maps one or more keys to the specified value. |
4 | Set entrySet() <br>Returns a Set view of the mappings contained in this map. |
5 | boolean equals(Object obj) <br>Compares the specified object with this map for equality. |
6 | Object get(Object k) <br>Returns the value to which this map maps the specified key, or null if the map contains no mapping for this key. |
7 | int hashCode() <br>Returns the hash code value for this map. |
8 | boolean isEmpty() <br>Returns true if this map contains no key-value mappings. |
9 | Set keySet() <br>Returns a Set view of the keys contained in this map. |
10 | Object put(Object k, Object v) <br>Associates the specified value with the specified key in this map (optional operation). |
11 | void putAll(Map m) <br>Copies all of the mappings from the specified map to this map (optional operation). |
12 | Object remove(Object k) <br>Removes the mapping for this key from this map if it is present (optional operation). |
13 | int size() <br>Returns the number of key-value mappings in this map. |
14 | Collection values() <br>Returns a Collection view of the values contained in this map. |
Example
The following example demonstrates the functionality of the Map interface:
import java.util.*;
public class CollectionsDemo {
public static void main(String[] args) {
Map m1 = new HashMap();
m1.put("Zara", "8");
m1.put("Mahnaz", "31");
m1.put("Ayan", "12");
m1.put("Daisy", "14");
System.out.println();
System.out.println(" Map Elements");
System.out.print("\t" + m1);
}
}
The output of the above example is:
Map Elements
{Mahnaz=31, Ayan=12, Daisy=14, Zara=8}