java.util.AbstractMap Maven / Gradle / Ivy
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This work corresponds to the API signatures of JSR 219: Foundation
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*/
package java.util;
import java.util.Map.Entry;
/**
* This class provides a skeletal implementation of the Map
* interface, to minimize the effort required to implement this interface.
*
* To implement an unmodifiable map, the programmer needs only to extend this
* class and provide an implementation for the entrySet method, which
* returns a set-view of the map's mappings. Typically, the returned set
* will, in turn, be implemented atop AbstractSet. This set should
* not support the add or remove methods, and its iterator
* should not support the remove method.
*
* To implement a modifiable map, the programmer must additionally override
* this class's put method (which otherwise throws an
* UnsupportedOperationException), and the iterator returned by
* entrySet().iterator() must additionally implement its
* remove method.
*
* The programmer should generally provide a void (no argument) and map
* constructor, as per the recommendation in the Map interface
* specification.
*
* The documentation for each non-abstract methods in this class describes its
* implementation in detail. Each of these methods may be overridden if the
* map being implemented admits a more efficient implementation.
*
* This class is a member of the
*
* Java Collections Framework.
*
* @author Josh Bloch
* @version 1.21, 02/02/00
* @see Map
* @see Collection
* @since 1.2
*/
public abstract class AbstractMap implements Map
{
/**
* Sole constructor. (For invocation by subclass constructors, typically
* implicit.)
*/
protected AbstractMap() { }
/**
* Returns the number of key-value mappings in this map. If the map
* contains more than Integer.MAX_VALUE elements, returns
* Integer.MAX_VALUE.
*
* This implementation returns entrySet().size().
*
* @return the number of key-value mappings in this map.
*/
public int size() {
return 0;
}
/**
* Returns true if this map contains no key-value mappings.
*
* This implementation returns size() == 0.
*
* @return true if this map contains no key-value mappings.
*/
public boolean isEmpty() {
return false;
}
/**
* Returns true if this map maps one or more keys to this value.
* More formally, returns true if and only if this map contains
* at least one mapping to a value v such that (value==null ?
* v==null : value.equals(v)). This operation will probably require
* time linear in the map size for most implementations of map.
*
* This implementation iterates over entrySet() searching for an entry
* with the specified value. If such an entry is found, true is
* returned. If the iteration terminates without finding such an entry,
* false is returned. Note that this implementation requires
* linear time in the size of the map.
*
* @param value value whose presence in this map is to be tested.
*
* @return true if this map maps one or more keys to this value.
*/
public boolean containsValue(Object value) {
return false;
}
/**
* Returns true if this map contains a mapping for the specified
* key.
*
* This implementation iterates over entrySet() searching for an
* entry with the specified key. If such an entry is found, true
* is returned. If the iteration terminates without finding such an
* entry, false is returned. Note that this implementation
* requires linear time in the size of the map; many implementations will
* override this method.
*
* @param key key whose presence in this map is to be tested.
* @return true if this map contains a mapping for the specified
* key.
*
* @throws NullPointerException key is null and this map does not
* not permit null keys.
*/
public boolean containsKey(Object key) {
return false;
}
/**
* Returns the value to which this map maps the specified key. Returns
* null if the map contains no mapping for this key. A return
* value of null does not necessarily indicate that the
* map contains no mapping for the key; it's also possible that the map
* explicitly maps the key to null. The containsKey operation
* may be used to distinguish these two cases.
*
* This implementation iterates over entrySet() searching for an
* entry with the specified key. If such an entry is found, the entry's
* value is returned. If the iteration terminates without finding such an
* entry, null is returned. Note that this implementation
* requires linear time in the size of the map; many implementations will
* override this method.
*
* @param key key whose associated value is to be returned.
* @return the value to which this map maps the specified key.
*
* @throws NullPointerException if the key is null and this map
* does not not permit null keys.
*
* @see #containsKey(Object)
*/
public Object get(Object key) {
return null;
}
/**
* Associates the specified value with the specified key in this map
* (optional operation). If the map previously contained a mapping for
* this key, the old value is replaced.
*
* This implementation always throws an
* UnsupportedOperationException.
*
* @param key key with which the specified value is to be associated.
* @param value value to be associated with the specified key.
*
* @return previous value associated with specified key, or null
* if there was no mapping for key. (A null return can
* also indicate that the map previously associated null
* with the specified key, if the implementation supports
* null values.)
*
* @throws UnsupportedOperationException if the put operation is
* not supported by this map.
*
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map.
*
* @throws IllegalArgumentException if some aspect of this key or value *
* prevents it from being stored in this map.
*
* @throws NullPointerException this map does not permit null
* keys or values, and the specified key or value is
* null.
*/
public Object put(Object key, Object value) {
return null;
}
/**
* Removes the mapping for this key from this map if present (optional
* operation).
*
* This implementation iterates over entrySet() searching for an
* entry with the specified key. If such an entry is found, its value is
* obtained with its getValue operation, the entry is is removed
* from the Collection (and the backing map) with the iterator's
* remove operation, and the saved value is returned. If the
* iteration terminates without finding such an entry, null is
* returned. Note that this implementation requires linear time in the
* size of the map; many implementations will override this method.
*
* Note that this implementation throws an
* UnsupportedOperationException if the entrySet iterator
* does not support the remove method and this map contains a
* mapping for the specified key.
*
* @param key key whose mapping is to be removed from the map.
* @return previous value associated with specified key, or null
* if there was no entry for key. (A null return can
* also indicate that the map previously associated null
* with the specified key, if the implementation supports
* null values.)
* @throws UnsupportedOperationException if the remove operation
* is not supported by this map.
*/
public Object remove(Object key) {
return null;
}
/**
* Copies all of the mappings from the specified map to this map
* (optional operation). These mappings will replace any mappings that
* this map had for any of the keys currently in the specified map.
*
* This implementation iterates over the specified map's
* entrySet() collection, and calls this map's put
* operation once for each entry returned by the iteration.
*
* Note that this implementation throws an
* UnsupportedOperationException if this map does not support
* the put operation and the specified map is nonempty.
*
* @param t mappings to be stored in this map.
*
* @throws UnsupportedOperationException if the putAll operation
* is not supported by this map.
*
* @throws ClassCastException if the class of a key or value in the
* specified map prevents it from being stored in this map.
*
* @throws IllegalArgumentException if some aspect of a key or value in
* the specified map prevents it from being stored in this map.
* @throws NullPointerException the specified map is null, or if
* this map does not permit null keys or values, and the
* specified map contains null keys or values.
*/
public void putAll(Map t) { }
/**
* Removes all mappings from this map (optional operation).
*
* This implementation calls entrySet().clear().
*
* Note that this implementation throws an
* UnsupportedOperationException if the entrySet
* does not support the clear operation.
*
* @throws UnsupportedOperationException clear is not supported
* by this map.
*/
public void clear() { }
/**
* Returns a Set view of the keys contained in this map. The Set is
* backed by the map, so changes to the map are reflected in the Set,
* and vice-versa. (If the map is modified while an iteration over
* the Set is in progress, the results of the iteration are undefined.)
* The Set supports element removal, which removes the corresponding entry
* from the map, via the Iterator.remove, Set.remove, removeAll
* retainAll, and clear operations. It does not support the add or
* addAll operations.
*
* This implementation returns a Set that subclasses
* AbstractSet. The subclass's iterator method returns a "wrapper
* object" over this map's entrySet() iterator. The size method delegates
* to this map's size method and the contains method delegates to this
* map's containsKey method.
*
* The Set is created the first time this method is called,
* and returned in response to all subsequent calls. No synchronization
* is performed, so there is a slight chance that multiple calls to this
* method will not all return the same Set.
*
* @return a Set view of the keys contained in this map.
*/
public Set keySet() {
return null;
}
/**
* Returns a collection view of the values contained in this map. The
* collection is backed by the map, so changes to the map are reflected in
* the collection, and vice-versa. (If the map is modified while an
* iteration over the collection is in progress, the results of the
* iteration are undefined.) The collection supports element removal,
* which removes the corresponding entry from the map, via the
* Iterator.remove, Collection.remove,
* removeAll, retainAll and clear operations.
* It does not support the add or addAll operations.
*
* This implementation returns a collection that subclasses abstract
* collection. The subclass's iterator method returns a "wrapper object"
* over this map's entrySet() iterator. The size method
* delegates to this map's size method and the contains method delegates
* to this map's containsValue method.
*
* The collection is created the first time this method is called, and
* returned in response to all subsequent calls. No synchronization is
* performed, so there is a slight chance that multiple calls to this
* method will not all return the same Collection.
*
* @return a collection view of the values contained in this map.
*/
public Collection values() {
return null;
}
/**
* Returns a set view of the mappings contained in this map. Each element
* in this set is a Map.Entry. The set is backed by the map, so changes
* to the map are reflected in the set, and vice-versa. (If the map is
* modified while an iteration over the set is in progress, the results of
* the iteration are undefined.) The set supports element removal, which
* removes the corresponding entry from the map, via the
* Iterator.remove, Set.remove, removeAll,
* retainAll and clear operations. It does not support
* the add or addAll operations.
*
* @return a set view of the mappings contained in this map.
*/
public abstract Set entrySet();
/**
* Compares the specified object with this map for equality. Returns
* true if the given object is also a map and the two maps
* represent the same mappings. More formally, two maps t1 and
* t2 represent the same mappings if
* t1.keySet().equals(t2.keySet()) and for every key k
* in t1.keySet(), (t1.get(k)==null ? t2.get(k)==null :
* t1.get(k).equals(t2.get(k))) . This ensures that the
* equals method works properly across different implementations
* of the map interface.
*
* This implementation first checks if the specified object is this map;
* if so it returns true. Then, it checks if the specified
* object is a map whose size is identical to the size of this set; if
* not, it it returns false. If so, it iterates over this map's
* entrySet collection, and checks that the specified map
* contains each mapping that this map contains. If the specified map
* fails to contain such a mapping, false is returned. If the
* iteration completes, true is returned.
*
* @param o object to be compared for equality with this map.
* @return true if the specified object is equal to this map.
*/
public boolean equals(Object o) {
return false;
}
/**
* Returns the hash code value for this map. The hash code of a map is
* defined to be the sum of the hash codes of each entry in the map's
* entrySet() view. This ensures that t1.equals(t2)
* implies that t1.hashCode()==t2.hashCode() for any two maps
* t1 and t2, as required by the general contract of
* Object.hashCode.
*
* This implementation iterates over entrySet(), calling
* hashCode on each element (entry) in the Collection, and adding
* up the results.
*
* @return the hash code value for this map.
* @see Map.Entry#hashCode()
* @see Object#hashCode()
* @see Object#equals(Object)
* @see Set#equals(Object)
*/
public int hashCode() {
return 0;
}
/**
* Returns a string representation of this map. The string representation
* consists of a list of key-value mappings in the order returned by the
* map's entrySet view's iterator, enclosed in braces
* ("{}"). Adjacent mappings are separated by the characters
* ", " (comma and space). Each key-value mapping is rendered as
* the key followed by an equals sign ("=") followed by the
* associated value. Keys and values are converted to strings as by
* String.valueOf(Object).
*
* This implementation creates an empty string buffer, appends a left
* brace, and iterates over the map's entrySet view, appending
* the string representation of each map.entry in turn. After
* appending each entry except the last, the string ", " is
* appended. Finally a right brace is appended. A string is obtained
* from the stringbuffer, and returned.
*
* @return a String representation of this map.
*/
public String toString() {
return null;
}
/**
* Returns a shallow copy of this AbstractMap instance: the keys
* and values themselves are not cloned.
*
* @return a shallow copy of this map.
*/
protected Object clone() throws CloneNotSupportedException {
return null;
}
}