/*
* @(#)AbstractMap.java 1.42 04/02/19
*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util;
import java.util.Map.Entry;
/**
* This class provides a skeletal implementation of the <tt>Map</tt>
* interface, to minimize the effort required to implement this interface. <p>
*
* To implement an unmodifiable map, the programmer needs only to extend this
* class and provide an implementation for the <tt>entrySet</tt> method, which
* returns a set-view of the map's mappings. Typically, the returned set
* will, in turn, be implemented atop <tt>AbstractSet</tt>. This set should
* not support the <tt>add</tt> or <tt>remove</tt> methods, and its iterator
* should not support the <tt>remove</tt> method.<p>
*
* To implement a modifiable map, the programmer must additionally override
* this class's <tt>put</tt> method (which otherwise throws an
* <tt>UnsupportedOperationException</tt>), and the iterator returned by
* <tt>entrySet().iterator()</tt> must additionally implement its
* <tt>remove</tt> method.<p>
*
* The programmer should generally provide a void (no argument) and map
* constructor, as per the recommendation in the <tt>Map</tt> interface
* specification.<p>
*
* 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.<p>
*
* This class is a member of the
* <a href="{@docRoot}/../guide/collections/index.html">
* Java Collections Framework</a>.
*
* @author Josh Bloch
* @author Neal Gafter
* @version 1.42, 02/19/04
* @see Map
* @see Collection
* @since 1.2
*/
public abstract class AbstractMap<K,V> implements Map<K,V> {
/**
* Sole constructor. (For invocation by subclass constructors, typically
* implicit.)
*/
protected AbstractMap() {
}
// Query Operations
/**
* Returns the number of key-value mappings in this map. If the map
* contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
* <tt>Integer.MAX_VALUE</tt>.<p>
*
* This implementation returns <tt>entrySet().size()</tt>.
*
* @return the number of key-value mappings in this map.
*/
public int size() {
return entrySet().size();
}
/**
* Returns <tt>true</tt> if this map contains no key-value mappings. <p>
*
* This implementation returns <tt>size() == 0</tt>.
*
* @return <tt>true</tt> if this map contains no key-value mappings.
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Returns <tt>true</tt> if this map maps one or more keys to this value.
* More formally, returns <tt>true</tt> if and only if this map contains
* at least one mapping to a value <tt>v</tt> such that <tt>(value==null ?
* v==null : value.equals(v))</tt>. This operation will probably require
* time linear in the map size for most implementations of map.<p>
*
* This implementation iterates over entrySet() searching for an entry
* with the specified value. If such an entry is found, <tt>true</tt> is
* returned. If the iteration terminates without finding such an entry,
* <tt>false</tt> 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 <tt>true</tt> if this map maps one or more keys to this value.
*/
public boolean containsValue(Object value) {
Iterator<Entry<K,V>> i = entrySet().iterator();
if (value==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getValue()==null)
return true;
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (value.equals(e.getValue()))
return true;
}
}
return false;
}
/**
* Returns <tt>true</tt> if this map contains a mapping for the specified
* key. <p>
*
* This implementation iterates over <tt>entrySet()</tt> searching for an
* entry with the specified key. If such an entry is found, <tt>true</tt>
* is returned. If the iteration terminates without finding such an
* entry, <tt>false</tt> 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 <tt>true</tt> if this map contains a mapping for the specified
* key.
*
* @throws NullPointerException if the key is <tt>null</tt> and this map
* does not permit <tt>null</tt> keys.
*/
public boolean containsKey(Object key) {
Iterator<Map.Entry<K,V>> i = entrySet().iterator();
if (key==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
return true;
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
return true;
}
}
return false;
}
/**
* Returns the value to which this map maps the specified key. Returns
* <tt>null</tt> if the map contains no mapping for this key. A return
* value of <tt>null</tt> does not <i>necessarily</i> indicate that the
* map contains no mapping for the key; it's also possible that the map
* explicitly maps the key to <tt>null</tt>. The containsKey operation
* may be used to distinguish these two cases. <p>
*
* This implementation iterates over <tt>entrySet()</tt> 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, <tt>null</tt> 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 <tt>null</tt> and this map
* does not permit <tt>null</tt> keys.
*
* @see #containsKey(Object)
*/
public V get(Object key) {
Iterator<Entry<K,V>> i = entrySet().iterator();
if (key==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
return e.getValue();
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
return e.getValue();
}
}
return null;
}
// Modification Operations
/**
* 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.<p>
*
* This implementation always throws an
* <tt>UnsupportedOperationException</tt>.
*
* @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 <tt>null</tt>
* if there was no mapping for key. (A <tt>null</tt> return can
* also indicate that the map previously associated <tt>null</tt>
* with the specified key, if the implementation supports
* <tt>null</tt> values.)
*
* @throws UnsupportedOperationException if the <tt>put</tt> 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 if this map does not permit <tt>null</tt>
* keys or values, and the specified key or value is
* <tt>null</tt>.
*/
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
/**
* Removes the mapping for this key from this map if present (optional
* operation). <p>
*
* This implementation iterates over <tt>entrySet()</tt> searching for an
* entry with the specified key. If such an entry is found, its value is
* obtained with its <tt>getValue</tt> operation, the entry is removed
* from the Collection (and the backing map) with the iterator's
* <tt>remove</tt> operation, and the saved value is returned. If the
* iteration terminates without finding such an entry, <tt>null</tt> is
* returned. Note that this implementation requires linear time in the
* size of the map; many implementations will override this method.<p>
*
* Note that this implementation throws an
* <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt> iterator
* does not support the <tt>remove</tt> 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 <tt>null</tt>
* if there was no entry for key. (A <tt>null</tt> return can
* also indicate that the map previously associated <tt>null</tt>
* with the specified key, if the implementation supports
* <tt>null</tt> values.)
* @throws UnsupportedOperationException if the <tt>remove</tt> operation
* is not supported by this map.
*/
public V remove(Object key) {
Iterator<Entry<K,V>> i = entrySet().iterator();
Entry<K,V> correctEntry = null;
if (key==null) {
while (correctEntry==null && i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
correctEntry = e;
}
} else {
while (correctEntry==null && i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
correctEntry = e;
}
}
V oldValue = null;
if (correctEntry !=null) {
oldValue = correctEntry.getValue();
i.remove();
}
return oldValue;
}
// Bulk Operations
/**
* 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.<p>
*
* This implementation iterates over the specified map's
* <tt>entrySet()</tt> collection, and calls this map's <tt>put</tt>
* operation once for each entry returned by the iteration.<p>
*
* Note that this implementation throws an
* <tt>UnsupportedOperationException</tt> if this map does not support
* the <tt>put</tt> operation and the specified map is nonempty.
*
* @param t mappings to be stored in this map.
*
* @throws UnsupportedOperationException if the <tt>putAll</tt> 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 if the specified map is <tt>null</tt>, or if
* this map does not permit <tt>null</tt> keys or values, and the
* specified map contains <tt>null</tt> keys or values.
*/
public void putAll(Map<? extends K, ? extends V> t) {
Iterator<? extends Entry<? extends K, ? extends V>> i = t.entrySet().iterator();
while (i.hasNext()) {
Entry<? extends K, ? extends V> e = i.next();
put(e.getKey(), e.getValue());
}
}
/**
* Removes all mappings from this map (optional operation). <p>
*
* This implementation calls <tt>entrySet().clear()</tt>.
*
* Note that this implementation throws an
* <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
* does not support the <tt>clear</tt> operation.
*
* @throws UnsupportedOperationException clear is not supported
* by this map.
*/
public void clear() {
entrySet().clear();
}
// Views
/**
* Each of these fields are initialized to contain an instance of the
* appropriate view the first time this view is requested. The views are
* stateless, so there's no reason to create more than one of each.
*/
transient volatile Set<K> keySet = null;
transient volatile Collection<V> values = null;
/**
* 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.<p>
*
* 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.<p>
*
* 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<K> keySet() {
if (keySet == null) {
keySet = new AbstractSet<K>() {
public Iterator<K> iterator() {
return new Iterator<K>() {
private Iterator<Entry<K,V>> i = entrySet().iterator();
public boolean hasNext() {
return i.hasNext();
}
public K next() {
return i.next().getKey();
}
public void remove() {
i.remove();
}
};
}
public int size() {
return AbstractMap.this.size();
}
public boolean contains(Object k) {
return AbstractMap.this.containsKey(k);
}
};
}
return keySet;
}
/**
* 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
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
* <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt> operations.
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations.<p>
*
* This implementation returns a collection that subclasses abstract
* collection. The subclass's iterator method returns a "wrapper object"
* over this map's <tt>entrySet()</tt> iterator. The size method
* delegates to this map's size method and the contains method delegates
* to this map's containsValue method.<p>
*
* 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<V> values() {
if (values == null) {
values = new AbstractCollection<V>() {
public Iterator<V> iterator() {
return new Iterator<V>() {
private Iterator<Entry<K,V>> i = entrySet().iterator();
public boolean hasNext() {
return i.hasNext();
}
public V next() {
return i.next().getValue();
}
public void remove() {
i.remove();
}
};
}
public int size() {
return AbstractMap.this.size();
}
public boolean contains(Object v) {
return AbstractMap.this.containsValue(v);
}
};
}
return values;
}
/**
* 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
* <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,
* <tt>retainAll</tt> and <tt>clear</tt> operations. It does not support
* the <tt>add</tt> or <tt>addAll</tt> operations.
*
* @return a set view of the mappings contained in this map.
*/
public abstract Set<Entry<K,V>> entrySet();
// Comparison and hashing
/**
* Compares the specified object with this map for equality. Returns
* <tt>true</tt> if the given object is also a map and the two maps
* represent the same mappings. More formally, two maps <tt>t1</tt> and
* <tt>t2</tt> represent the same mappings if
* <tt>t1.keySet().equals(t2.keySet())</tt> and for every key <tt>k</tt>
* in <tt>t1.keySet()</tt>, <tt> (t1.get(k)==null ? t2.get(k)==null :
* t1.get(k).equals(t2.get(k))) </tt>. This ensures that the
* <tt>equals</tt> method works properly across different implementations
* of the map interface.<p>
*
* This implementation first checks if the specified object is this map;
* if so it returns <tt>true</tt>. Then, it checks if the specified
* object is a map whose size is identical to the size of this set; if
* not, it returns <tt>false</tt>. If so, it iterates over this map's
* <tt>entrySet</tt> collection, and checks that the specified map
* contains each mapping that this map contains. If the specified map
* fails to contain such a mapping, <tt>false</tt> is returned. If the
* iteration completes, <tt>true</tt> is returned.
*
* @param o object to be compared for equality with this map.
* @return <tt>true</tt> if the specified object is equal to this map.
*/
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Map))
return false;
Map<K,V> t = (Map<K,V>) o;
if (t.size() != size())
return false;
try {
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext()) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
if (value == null) {
if (!(t.get(key)==null && t.containsKey(key)))
return false;
} else {
if (!value.equals(t.get(key)))
return false;
}
}
} catch(ClassCastException unused) {
return false;
} catch(NullPointerException unused) {
return false;
}
return true;
}
/**
* 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
* <tt>entrySet()</tt> view. This ensures that <tt>t1.equals(t2)</tt>
* implies that <tt>t1.hashCode()==t2.hashCode()</tt> for any two maps
* <tt>t1</tt> and <tt>t2</tt>, as required by the general contract of
* Object.hashCode.<p>
*
* This implementation iterates over <tt>entrySet()</tt>, calling
* <tt>hashCode</tt> 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() {
int h = 0;
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext())
h += i.next().hashCode();
return h;
}
/**
* 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 <tt>entrySet</tt> view's iterator, enclosed in braces
* (<tt>"{}"</tt>). Adjacent mappings are separated by the characters
* <tt>", "</tt> (comma and space). Each key-value mapping is rendered as
* the key followed by an equals sign (<tt>"="</tt>) followed by the
* associated value. Keys and values are converted to strings as by
* <tt>String.valueOf(Object)</tt>.<p>
*
* This implementation creates an empty string buffer, appends a left
* brace, and iterates over the map's <tt>entrySet</tt> view, appending
* the string representation of each <tt>map.entry</tt> in turn. After
* appending each entry except the last, the string <tt>", "</tt> 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() {
StringBuffer buf = new StringBuffer();
buf.append("{");
Iterator<Entry<K,V>> i = entrySet().iterator();
boolean hasNext = i.hasNext();
while (hasNext) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
if (key == this)
buf.append("(this Map)");
else
buf.append(key);
buf.append("=");
if (value == this)
buf.append("(this Map)");
else
buf.append(value);
hasNext = i.hasNext();
if (hasNext)
buf.append(", ");
}
buf.append("}");
return buf.toString();
}
/**
* Returns a shallow copy of this <tt>AbstractMap</tt> instance: the keys
* and values themselves are not cloned.
*
* @return a shallow copy of this map.
*/
protected Object clone() throws CloneNotSupportedException {
AbstractMap<K,V> result = (AbstractMap<K,V>)super.clone();
result.keySet = null;
result.values = null;
return result;
}
/**
* This should be made public as soon as possible. It greatly simplifies
* the task of implementing Map.
*/
static class SimpleEntry<K,V> implements Entry<K,V> {
K key;
V value;
public SimpleEntry(K key, V value) {
this.key = key;
this.value = value;
}
public SimpleEntry(Entry<K,V> e) {
this.key = e.getKey();
this.value = e.getValue();
}
public K getKey() {
return key;
}
public V getValue() {
return value;
}
public V setValue(V value) {
V oldValue = this.value;
this.value = value;
return oldValue;
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry)o;
return eq(key, e.getKey()) && eq(value, e.getValue());
}
public int hashCode() {
return ((key == null) ? 0 : key.hashCode()) ^
((value == null) ? 0 : value.hashCode());
}
public String toString() {
return key + "=" + value;
}
private static boolean eq(Object o1, Object o2) {
return (o1 == null ? o2 == null : o1.equals(o2));
}
}
}
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