Summary of Classes and Interfaces - Absolute Java - page 1182

Map<K,V> Interface
Package: java.util
Ancestor interfaces: none
All the exception classes mentioned are unchecked exceptions, which means they are not
required to be caught in a catch block or declared in a throws clause. No import statement is
required because these exception classes are in the package java.lang .
CONSTRUCTORS
Although not offi cially required by the interface, any class that implements the Map<K,V>
interface should have at least two constructors: a no-argument constructor that creates an empty
Map<K,V> object, and a constructor with one Map<K,V> parameter that creates a Map<K,V>
object with the same elements as the constructor argument. The interface does not specify
whether the copy produced by the one-argument constructor is a shallow copy or a deep copy of
its argument.
METHODS
public boolean containsKey(Object key)
Returns true if the calling object contains key as one of its keys.
Throws:
ClassCastException if the type of key is incompatible with the type for this map (optional).
NullPointerException if the key is null and this map does not permit null keys (optional).
public boolean containsValue(Object value)
Returns true if the calling object contains one or more keys that map to an instance of value .
Throws:
ClassCastException if the type of value is incompatible with the type for this map (optional).
NullPointerException if the value is null and this map does not permit null
values (optional).
public Set<Map.Entry<K,V>> entrySet()
Returns a set view consisting of (key, value) mappings for all entries in the map. Changes to the
map are refl ected in the set and vice-versa.
public boolean equals(Object other)
This is the equals of the map, not the equals of the elements in the map. Overrides the
inherited method equals .
public V get(Object key)
Returns the value onto which the calling object maps key . If key is not in the map, then null
is returned. Note that this does not always mean that the key is not in the map, because it
is possible to map a key to null . The containsKey method can be used to distinguish the
two cases.
Throws:
ClassCastException if the type of key is incompatible with the type for this map (optional).
NullPointerException if the key is null and this map does not permit null keys (optional).