Map集合結合一覽圖
Map集合：大部分比較重要的數據結構需要實現的接口
public interface Map<K, V> {
// Query Operations
/**
* Returns the number of key-value mappings in this map. If the
* map contains more than {@code Integer.MAX_VALUE} elements, returns
* {@code Integer.MAX_VALUE}.
*
* @return the number of key-value mappings in this map
返回K-V對的數量，數量超過Integer.MAX_VALUE，返回Integer.MAX_VALUE
*/
int size();
/**
* Returns {@code true} if this map contains no key-value mappings.
*
* @return {@code true} if this map contains no key-value mappings
判斷map中沒有包含任何k-v對
*/
boolean isEmpty();
/**
判斷是否包含指定key的k-v存在則返回true
*/
boolean containsKey(Object key);
/**
判斷是否包含指定value的k-v存在則返回true
*/
boolean containsValue(Object value);
/**
返回與key對應的value,
*/
V get(Object key);
// Modification Operations 修改操作
/**
將指定的k-v放入map,如果之前存在與k相等的k-v對，則更新v的值
返回舊值或null
*/
V put(K key, V value);
/**
刪除指定的k的k-v，返回舊值或null
*/
V remove(Object key);
// Bulk Operations
/**
批量操作，將指定map全部放入，相當於對次put操作
*/
void putAll(Map<? extends K, ? extends V> m);
/**
刪除所有k-v
*/
void clear();
// Views
/**
返回map中所有key的set類型
*/
Set<K> keySet();
/**
返回map中所有value的Collection類型
*/
Collection<V> values();
/**
返回map中所有k-v對的Set<Map.Entry<K,V>>類型
*/
Set<Map.Entry<K, V>> entrySet();
/**
* A map entry (key-value pair). The {@code Map.entrySet} method returns
* a collection-view of the map, whose elements are of this class. The
* <i>only</i> way to obtain a reference to a map entry is from the
* iterator of this collection-view. These {@code Map.Entry} objects are
* valid <i>only</i> for the duration of the iteration; more formally,
* the behavior of a map entry is undefined if the backing map has been
* modified after the entry was returned by the iterator, except through
* the {@code setValue} operation on the map entry.
*
* @see Map#entrySet()
* @since 1.2
內部接口
*/
interface Entry<K, V> {
/**
返回這個Entry的key
*/
K getKey();
/**
返回這個Entry的key
*/
V getValue();
/**
設置value並返回這個Entry的舊value
*/
V setValue(V value);
/**
將此Entry與o進行比較
*/
boolean equals(Object o);
/**
獲取此對象的hashcode
*/
int hashCode();
/**
接口靜態方法：
返回一個比較器（通過對key自然順序的比較）
*/
public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K, V>> comparingByKey() {
return (Comparator<Map.Entry<K, V>> & Serializable)
(c1, c2) -> c1.getKey().compareTo(c2.getKey());
}
/**
返回一個比較器（通過對key自然順序的比較）
* @since 1.8
*/
public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K, V>> comparingByValue() {
return (Comparator<Map.Entry<K, V>> & Serializable)
(c1, c2) -> c1.getValue().compareTo(c2.getValue());
}
/**
通過指定一個key類型的比較器並返回一個比較器（通過對key自然順序的比較）
*/
public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
Objects.requireNonNull(cmp);
return (Comparator<Map.Entry<K, V>> & Serializable)
(c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
}
/**
通過指定一個value類型的比較器並返回一個比較器（通過對value自然順序的比較）
*/
public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
Objects.requireNonNull(cmp);
return (Comparator<Map.Entry<K, V>> & Serializable)
(c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
}
}
// Comparison and hashing
/**
比較是否相等
*/
boolean equals(Object o);
/**
獲取hashcode
*/
int hashCode();
// Defaultable methods
/**
* Returns the value to which the specified key is mapped, or
* {@code defaultValue} if this map contains no mapping for the key.
*
* @implSpec
* The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties.
*
* @param key the key whose associated value is to be returned
* @param defaultValue the default mapping of the key
* @return the value to which the specified key is mapped, or
* {@code defaultValue} if this map contains no mapping for the key
* @throws ClassCastException if the key is of an inappropriate type for
* this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified key is null and this map
* does not permit null keys
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @since 1.8
*/
default V getOrDefault(Object key, V defaultValue) {
V v;
return (((v = get(key)) != null) || containsKey(key))
? v
: defaultValue;
}
/**
* Performs the given action for each entry in this map until all entries
* have been processed or the action throws an exception. Unless
* otherwise specified by the implementing class, actions are performed in
* the order of entry set iteration (if an iteration order is specified.)
* Exceptions thrown by the action are relayed to the caller.
*
* @implSpec
* The default implementation is equivalent to, for this {@code map}:
* <pre> {@code
* for (Map.Entry<K, V> entry : map.entrySet())
* action.accept(entry.getKey(), entry.getValue());
* }</pre>
*
* The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties.
*
* @param action The action to be performed for each entry
* @throws NullPointerException if the specified action is null
* @throws ConcurrentModificationException if an entry is found to be
* removed during iteration
* @since 1.8
*/
default void forEach(BiConsumer<? super K, ? super V> action) {
Objects.requireNonNull(action);
for (Map.Entry<K, V> entry : entrySet()) {
K k;
V v;
try {
k = entry.getKey();
v = entry.getValue();
} catch (IllegalStateException ise) {
// this usually means the entry is no longer in the map.
throw new ConcurrentModificationException(ise);
}
action.accept(k, v);
}
}
/**
* Replaces each entry's value with the result of invoking the given
* function on that entry until all entries have been processed or the
* function throws an exception. Exceptions thrown by the function are
* relayed to the caller.
*
* @implSpec
* <p>The default implementation is equivalent to, for this {@code map}:
* <pre> {@code
* for (Map.Entry<K, V> entry : map.entrySet())
* entry.setValue(function.apply(entry.getKey(), entry.getValue()));
* }</pre>
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties.
*
* @param function the function to apply to each entry
* @throws UnsupportedOperationException if the {@code set} operation
* is not supported by this map's entry set iterator.
* @throws ClassCastException if the class of a replacement value
* prevents it from being stored in this map
* @throws NullPointerException if the specified function is null, or the
* specified replacement value is null, and this map does not permit null
* values
* @throws ClassCastException if a replacement value is of an inappropriate
* type for this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if function or a replacement value is null,
* and this map does not permit null keys or values
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws IllegalArgumentException if some property of a replacement value
* prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ConcurrentModificationException if an entry is found to be
* removed during iteration
* @since 1.8
*/
default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
Objects.requireNonNull(function);
for (Map.Entry<K, V> entry : entrySet()) {
K k;
V v;
try {
k = entry.getKey();
v = entry.getValue();
} catch (IllegalStateException ise) {
// this usually means the entry is no longer in the map.
throw new ConcurrentModificationException(ise);
}
// ise thrown from function is not a cme.
v = function.apply(k, v);
try {
entry.setValue(v);
} catch (IllegalStateException ise) {
// this usually means the entry is no longer in the map.
throw new ConcurrentModificationException(ise);
}
}
}
/**
* If the specified key is not already associated with a value (or is mapped
* to {@code null}) associates it with the given value and returns
* {@code null}, else returns the current value.
*
* @implSpec
* The default implementation is equivalent to, for this {@code
* map}:
*
* <pre> {@code
* V v = map.get(key);
* if (v == null)
* v = map.put(key, value);
*
* return v;
* }</pre>
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties.
*
* @param key key with which the specified value is to be associated
* @param value value to be associated with the specified key
* @return the previous value associated with the specified key, or
* {@code null} if there was no mapping for the key.
* (A {@code null} return can also indicate that the map
* previously associated {@code null} with the key,
* if the implementation supports null values.)
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if the key or value is of an inappropriate
* type for this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified key or value is null,
* and this map does not permit null keys or values
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @since 1.8
*/
default V putIfAbsent(K key, V value) {
V v = get(key);
if (v == null) {
v = put(key, value);
}
return v;
}
/**
* Removes the entry for the specified key only if it is currently
* mapped to the specified value.
*
* @implSpec
* The default implementation is equivalent to, for this {@code map}:
*
* <pre> {@code
* if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
* map.remove(key);
* return true;
* } else
* return false;
* }</pre>
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties.
*
* @param key key with which the specified value is associated
* @param value value expected to be associated with the specified key
* @return {@code true} if the value was removed
* @throws UnsupportedOperationException if the {@code remove} operation
* is not supported by this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if the key or value is of an inappropriate
* type for this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified key or value is null,
* and this map does not permit null keys or values
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @since 1.8
*/
default boolean remove(Object key, Object value) {
Object curValue = get(key);
if (!Objects.equals(curValue, value) ||
(curValue == null && !containsKey(key))) {
return false;
}
remove(key);
return true;
}
/**
* Replaces the entry for the specified key only if currently
* mapped to the specified value.
*
* @implSpec
* The default implementation is equivalent to, for this {@code map}:
*
* <pre> {@code
* if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
* map.put(key, newValue);
* return true;
* } else
* return false;
* }</pre>
*
* The default implementation does not throw NullPointerException
* for maps that do not support null values if oldValue is null unless
* newValue is also null.
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties.
*
* @param key key with which the specified value is associated
* @param oldValue value expected to be associated with the specified key
* @param newValue value to be associated with the specified key
* @return {@code true} if the value was replaced
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if the class of a specified key or value
* prevents it from being stored in this map
* @throws NullPointerException if a specified key or newValue is null,
* and this map does not permit null keys or values
* @throws NullPointerException if oldValue is null and this map does not
* permit null values
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws IllegalArgumentException if some property of a specified key
* or value prevents it from being stored in this map
* @since 1.8
*/
default boolean replace(K key, V oldValue, V newValue) {
Object curValue = get(key);
if (!Objects.equals(curValue, oldValue) ||
(curValue == null && !containsKey(key))) {
return false;
}
put(key, newValue);
return true;
}
/**
* Replaces the entry for the specified key only if it is
* currently mapped to some value.
*
* @implSpec
* The default implementation is equivalent to, for this {@code map}:
*
* <pre> {@code
* if (map.containsKey(key)) {
* return map.put(key, value);
* } else
* return null;
* }</pre>
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties.
*
* @param key key with which the specified value is associated
* @param value value to be associated with the specified key
* @return the previous value associated with the specified key, or
* {@code null} if there was no mapping for the key.
* (A {@code null} return can also indicate that the map
* previously associated {@code null} with the key,
* if the implementation supports null values.)
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified key or value is null,
* and this map does not permit null keys or values
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map
* @since 1.8
*/
default V replace(K key, V value) {
V curValue;
if (((curValue = get(key)) != null) || containsKey(key)) {
curValue = put(key, value);
}
return curValue;
}
/**
* If the specified key is not already associated with a value (or is mapped
* to {@code null}), attempts to compute its value using the given mapping
* function and enters it into this map unless {@code null}.
*
* <p>If the mapping function returns {@code null}, no mapping is recorded.
* If the mapping function itself throws an (unchecked) exception, the
* exception is rethrown, and no mapping is recorded. The most
* common usage is to construct a new object serving as an initial
* mapped value or memoized result, as in:
*
* <pre> {@code
* map.computeIfAbsent(key, k -> new Value(f(k)));
* }</pre>
*
* <p>Or to implement a multi-value map, {@code Map<K,Collection<V>>},
* supporting multiple values per key:
*
* <pre> {@code
* map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
* }</pre>
*
* <p>The mapping function should not modify this map during computation.
*
* @implSpec
* The default implementation is equivalent to the following steps for this
* {@code map}, then returning the current value or {@code null} if now
* absent:
*
* <pre> {@code
* if (map.get(key) == null) {
* V newValue = mappingFunction.apply(key);
* if (newValue != null)
* map.put(key, newValue);
* }
* }</pre>
*
* <p>The default implementation makes no guarantees about detecting if the
* mapping function modifies this map during computation and, if
* appropriate, reporting an error. Non-concurrent implementations should
* override this method and, on a best-effort basis, throw a
* {@code ConcurrentModificationException} if it is detected that the
* mapping function modifies this map during computation. Concurrent
* implementations should override this method and, on a best-effort basis,
* throw an {@code IllegalStateException} if it is detected that the
* mapping function modifies this map during computation and as a result
* computation would never complete.
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties. In particular, all implementations of
* subinterface {@link java.util.concurrent.ConcurrentMap} must document
* whether the mapping function is applied once atomically only if the value
* is not present.
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the mapping function to compute a value
* @return the current (existing or computed) value associated with
* the specified key, or null if the computed value is null
* @throws NullPointerException if the specified key is null and
* this map does not support null keys, or the mappingFunction
* is null
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @since 1.8
*/
default V computeIfAbsent(K key,
Function<? super K, ? extends V> mappingFunction) {
Objects.requireNonNull(mappingFunction);
V v;
if ((v = get(key)) == null) {
V newValue;
if ((newValue = mappingFunction.apply(key)) != null) {
put(key, newValue);
return newValue;
}
}
return v;
}
/**
* If the value for the specified key is present and non-null, attempts to
* compute a new mapping given the key and its current mapped value.
*
* <p>If the remapping function returns {@code null}, the mapping is removed.
* If the remapping function itself throws an (unchecked) exception, the
* exception is rethrown, and the current mapping is left unchanged.
*
* <p>The remapping function should not modify this map during computation.
*
* @implSpec
* The default implementation is equivalent to performing the following
* steps for this {@code map}, then returning the current value or
* {@code null} if now absent:
*
* <pre> {@code
* if (map.get(key) != null) {
* V oldValue = map.get(key);
* V newValue = remappingFunction.apply(key, oldValue);
* if (newValue != null)
* map.put(key, newValue);
* else
* map.remove(key);
* }
* }</pre>
*
* <p>The default implementation makes no guarantees about detecting if the
* remapping function modifies this map during computation and, if
* appropriate, reporting an error. Non-concurrent implementations should
* override this method and, on a best-effort basis, throw a
* {@code ConcurrentModificationException} if it is detected that the
* remapping function modifies this map during computation. Concurrent
* implementations should override this method and, on a best-effort basis,
* throw an {@code IllegalStateException} if it is detected that the
* remapping function modifies this map during computation and as a result
* computation would never complete.
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties. In particular, all implementations of
* subinterface {@link java.util.concurrent.ConcurrentMap} must document
* whether the remapping function is applied once atomically only if the
* value is not present.
*
* @param key key with which the specified value is to be associated
* @param remappingFunction the remapping function to compute a value
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key is null and
* this map does not support null keys, or the
* remappingFunction is null
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @since 1.8
*/
default V computeIfPresent(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
Objects.requireNonNull(remappingFunction);
V oldValue;
if ((oldValue = get(key)) != null) {
V newValue = remappingFunction.apply(key, oldValue);
if (newValue != null) {
put(key, newValue);
return newValue;
} else {
remove(key);
return null;
}
} else {
return null;
}
}
/**
* Attempts to compute a mapping for the specified key and its current
* mapped value (or {@code null} if there is no current mapping). For
* example, to either create or append a {@code String} msg to a value
* mapping:
*
* <pre> {@code
* map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
* (Method {@link #merge merge()} is often simpler to use for such purposes.)
*
* <p>If the remapping function returns {@code null}, the mapping is removed
* (or remains absent if initially absent). If the remapping function
* itself throws an (unchecked) exception, the exception is rethrown, and
* the current mapping is left unchanged.
*
* <p>The remapping function should not modify this map during computation.
*
* @implSpec
* The default implementation is equivalent to performing the following
* steps for this {@code map}, then returning the current value or
* {@code null} if absent:
*
* <pre> {@code
* V oldValue = map.get(key);
* V newValue = remappingFunction.apply(key, oldValue);
* if (oldValue != null) {
* if (newValue != null)
* map.put(key, newValue);
* else
* map.remove(key);
* } else {
* if (newValue != null)
* map.put(key, newValue);
* else
* return null;
* }
* }</pre>
*
* <p>The default implementation makes no guarantees about detecting if the
* remapping function modifies this map during computation and, if
* appropriate, reporting an error. Non-concurrent implementations should
* override this method and, on a best-effort basis, throw a
* {@code ConcurrentModificationException} if it is detected that the
* remapping function modifies this map during computation. Concurrent
* implementations should override this method and, on a best-effort basis,
* throw an {@code IllegalStateException} if it is detected that the
* remapping function modifies this map during computation and as a result
* computation would never complete.
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties. In particular, all implementations of
* subinterface {@link java.util.concurrent.ConcurrentMap} must document
* whether the remapping function is applied once atomically only if the
* value is not present.
*
* @param key key with which the specified value is to be associated
* @param remappingFunction the remapping function to compute a value
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key is null and
* this map does not support null keys, or the
* remappingFunction is null
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @since 1.8
*/
default V compute(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
Objects.requireNonNull(remappingFunction);
V oldValue = get(key);
V newValue = remappingFunction.apply(key, oldValue);
if (newValue == null) {
// delete mapping
if (oldValue != null || containsKey(key)) {
// something to remove
remove(key);
return null;
} else {
// nothing to do. Leave things as they were.
return null;
}
} else {
// add or replace old mapping
put(key, newValue);
return newValue;
}
}
/**
* If the specified key is not already associated with a value or is
* associated with null, associates it with the given non-null value.
* Otherwise, replaces the associated value with the results of the given
* remapping function, or removes if the result is {@code null}. This
* method may be of use when combining multiple mapped values for a key.
* For example, to either create or append a {@code String msg} to a
* value mapping:
*
* <pre> {@code
* map.merge(key, msg, String::concat)
* }</pre>
*
* <p>If the remapping function returns {@code null}, the mapping is removed.
* If the remapping function itself throws an (unchecked) exception, the
* exception is rethrown, and the current mapping is left unchanged.
*
* <p>The remapping function should not modify this map during computation.
*
* @implSpec
* The default implementation is equivalent to performing the following
* steps for this {@code map}, then returning the current value or
* {@code null} if absent:
*
* <pre> {@code
* V oldValue = map.get(key);
* V newValue = (oldValue == null) ? value :
* remappingFunction.apply(oldValue, value);
* if (newValue == null)
* map.remove(key);
* else
* map.put(key, newValue);
* }</pre>
*
* <p>The default implementation makes no guarantees about detecting if the
* remapping function modifies this map during computation and, if
* appropriate, reporting an error. Non-concurrent implementations should
* override this method and, on a best-effort basis, throw a
* {@code ConcurrentModificationException} if it is detected that the
* remapping function modifies this map during computation. Concurrent
* implementations should override this method and, on a best-effort basis,
* throw an {@code IllegalStateException} if it is detected that the
* remapping function modifies this map during computation and as a result
* computation would never complete.
*
* <p>The default implementation makes no guarantees about synchronization
* or atomicity properties of this method. Any implementation providing
* atomicity guarantees must override this method and document its
* concurrency properties. In particular, all implementations of
* subinterface {@link java.util.concurrent.ConcurrentMap} must document
* whether the remapping function is applied once atomically only if the
* value is not present.
*
* @param key key with which the resulting value is to be associated
* @param value the non-null value to be merged with the existing value
* associated with the key or, if no existing value or a null value
* is associated with the key, to be associated with the key
* @param remappingFunction the remapping function to recompute a value if
* present
* @return the new value associated with the specified key, or null if no
* value is associated with the key
* @throws UnsupportedOperationException if the {@code put} operation
* is not supported by this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws IllegalArgumentException if some property of the specified key
* or value prevents it from being stored in this map
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified key is null and this map
* does not support null keys or the value or remappingFunction is
* null
* @since 1.8
*/
default V merge(K key, V value,
BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
Objects.requireNonNull(remappingFunction);
Objects.requireNonNull(value);
V oldValue = get(key);
V newValue = (oldValue == null) ? value :
remappingFunction.apply(oldValue, value);
if (newValue == null) {
remove(key);
} else {
put(key, newValue);
}
return newValue;
}
/**
* Returns an unmodifiable map containing zero mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @return an empty {@code Map}
*
* @since 9
*/
static <K, V> Map<K, V> of() {
return ImmutableCollections.emptyMap();
}
/**
* Returns an unmodifiable map containing a single mapping.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the mapping's key
* @param v1 the mapping's value
* @return a {@code Map} containing the specified mapping
* @throws NullPointerException if the key or the value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1) {
return new ImmutableCollections.Map1<>(k1, v1);
}
/**
* Returns an unmodifiable map containing two mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if the keys are duplicates
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2);
}
/**
* Returns an unmodifiable map containing three mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @param k3 the third mapping's key
* @param v3 the third mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3);
}
/**
* Returns an unmodifiable map containing four mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @param k3 the third mapping's key
* @param v3 the third mapping's value
* @param k4 the fourth mapping's key
* @param v4 the fourth mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4);
}
/**
* Returns an unmodifiable map containing five mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @param k3 the third mapping's key
* @param v3 the third mapping's value
* @param k4 the fourth mapping's key
* @param v4 the fourth mapping's value
* @param k5 the fifth mapping's key
* @param v5 the fifth mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5);
}
/**
* Returns an unmodifiable map containing six mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @param k3 the third mapping's key
* @param v3 the third mapping's value
* @param k4 the fourth mapping's key
* @param v4 the fourth mapping's value
* @param k5 the fifth mapping's key
* @param v5 the fifth mapping's value
* @param k6 the sixth mapping's key
* @param v6 the sixth mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
K k6, V v6) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
k6, v6);
}
/**
* Returns an unmodifiable map containing seven mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @param k3 the third mapping's key
* @param v3 the third mapping's value
* @param k4 the fourth mapping's key
* @param v4 the fourth mapping's value
* @param k5 the fifth mapping's key
* @param v5 the fifth mapping's value
* @param k6 the sixth mapping's key
* @param v6 the sixth mapping's value
* @param k7 the seventh mapping's key
* @param v7 the seventh mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
K k6, V v6, K k7, V v7) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
k6, v6, k7, v7);
}
/**
* Returns an unmodifiable map containing eight mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @param k3 the third mapping's key
* @param v3 the third mapping's value
* @param k4 the fourth mapping's key
* @param v4 the fourth mapping's value
* @param k5 the fifth mapping's key
* @param v5 the fifth mapping's value
* @param k6 the sixth mapping's key
* @param v6 the sixth mapping's value
* @param k7 the seventh mapping's key
* @param v7 the seventh mapping's value
* @param k8 the eighth mapping's key
* @param v8 the eighth mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
K k6, V v6, K k7, V v7, K k8, V v8) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
k6, v6, k7, v7, k8, v8);
}
/**
* Returns an unmodifiable map containing nine mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @param k3 the third mapping's key
* @param v3 the third mapping's value
* @param k4 the fourth mapping's key
* @param v4 the fourth mapping's value
* @param k5 the fifth mapping's key
* @param v5 the fifth mapping's value
* @param k6 the sixth mapping's key
* @param v6 the sixth mapping's value
* @param k7 the seventh mapping's key
* @param v7 the seventh mapping's value
* @param k8 the eighth mapping's key
* @param v8 the eighth mapping's value
* @param k9 the ninth mapping's key
* @param v9 the ninth mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
k6, v6, k7, v7, k8, v8, k9, v9);
}
/**
* Returns an unmodifiable map containing ten mappings.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param k1 the first mapping's key
* @param v1 the first mapping's value
* @param k2 the second mapping's key
* @param v2 the second mapping's value
* @param k3 the third mapping's key
* @param v3 the third mapping's value
* @param k4 the fourth mapping's key
* @param v4 the fourth mapping's value
* @param k5 the fifth mapping's key
* @param v5 the fifth mapping's value
* @param k6 the sixth mapping's key
* @param v6 the sixth mapping's value
* @param k7 the seventh mapping's key
* @param v7 the seventh mapping's value
* @param k8 the eighth mapping's key
* @param v8 the eighth mapping's value
* @param k9 the ninth mapping's key
* @param v9 the ninth mapping's value
* @param k10 the tenth mapping's key
* @param v10 the tenth mapping's value
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any key or value is {@code null}
*
* @since 9
*/
static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10) {
return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
k6, v6, k7, v7, k8, v8, k9, v9, k10, v10);
}
/**
* Returns an unmodifiable map containing keys and values extracted from the given entries.
* The entries themselves are not stored in the map.
* See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
*
* @apiNote
* It is convenient to create the map entries using the {@link Map#entry Map.entry()} method.
* For example,
*
* <pre>{@code
* import static java.util.Map.entry;
*
* Map<Integer,String> map = Map.ofEntries(
* entry(1, "a"),
* entry(2, "b"),
* entry(3, "c"),
* ...
* entry(26, "z"));
* }</pre>
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param entries {@code Map.Entry}s containing the keys and values from which the map is populated
* @return a {@code Map} containing the specified mappings
* @throws IllegalArgumentException if there are any duplicate keys
* @throws NullPointerException if any entry, key, or value is {@code null}, or if
* the {@code entries} array is {@code null}
*
* @see Map#entry Map.entry()
* @since 9
*/
@SafeVarargs
@SuppressWarnings("varargs")
static <K, V> Map<K, V> ofEntries(Entry<? extends K, ? extends V>... entries) {
if (entries.length == 0) { // implicit null check of entries array
return ImmutableCollections.emptyMap();
} else if (entries.length == 1) {
// implicit null check of the array slot
return new ImmutableCollections.Map1<>(entries[0].getKey(),
entries[0].getValue());
} else {
Object[] kva = new Object[entries.length << 1];
int a = 0;
for (Entry<? extends K, ? extends V> entry : entries) {
// implicit null checks of each array slot
kva[a++] = entry.getKey();
kva[a++] = entry.getValue();
}
return new ImmutableCollections.MapN<>(kva);
}
}
/**
* Returns an unmodifiable {@link Entry} containing the given key and value.
* These entries are suitable for populating {@code Map} instances using the
* {@link Map#ofEntries Map.ofEntries()} method.
* The {@code Entry} instances created by this method have the following characteristics:
*
* <ul>
* <li>They disallow {@code null} keys and values. Attempts to create them using a {@code null}
* key or value result in {@code NullPointerException}.
* <li>They are unmodifiable. Calls to {@link Entry#setValue Entry.setValue()}
* on a returned {@code Entry} result in {@code UnsupportedOperationException}.
* <li>They are not serializable.
* <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>.
* Callers should make no assumptions about the identity of the returned instances.
* This method is free to create new instances or reuse existing ones. Therefore,
* identity-sensitive operations on these instances (reference equality ({@code ==}),
* identity hash code, and synchronization) are unreliable and should be avoided.
* </ul>
*
* @apiNote
* For a serializable {@code Entry}, see {@link AbstractMap.SimpleEntry} or
* {@link AbstractMap.SimpleImmutableEntry}.
*
* @param <K> the key's type
* @param <V> the value's type
* @param k the key
* @param v the value
* @return an {@code Entry} containing the specified key and value
* @throws NullPointerException if the key or value is {@code null}
*
* @see Map#ofEntries Map.ofEntries()
* @since 9
*/
static <K, V> Entry<K, V> entry(K k, V v) {
// KeyValueHolder checks for nulls
return new KeyValueHolder<>(k, v);
}
/**
* Returns an <a href="#unmodifiable">unmodifiable Map</a> containing the entries
* of the given Map. The given Map must not be null, and it must not contain any
* null keys or values. If the given Map is subsequently modified, the returned
* Map will not reflect such modifications.
*
* @implNote
* If the given Map is an <a href="#unmodifiable">unmodifiable Map</a>,
* calling copyOf will generally not create a copy.
*
* @param <K> the {@code Map}'s key type
* @param <V> the {@code Map}'s value type
* @param map a {@code Map} from which entries are drawn, must be non-null
* @return a {@code Map} containing the entries of the given {@code Map}
* @throws NullPointerException if map is null, or if it contains any null keys or values
* @since 10
*/
@SuppressWarnings({"rawtypes","unchecked"})
static <K, V> Map<K, V> copyOf(Map<? extends K, ? extends V> map) {
if (map instanceof ImmutableCollections.AbstractImmutableMap) {
return (Map<K,V>)map;
} else {
return (Map<K,V>)Map.ofEntries(map.entrySet().toArray(new Entry[0]));
}
}
}
AbstractMap：AbstractMap 是map接口的實現類之一，也是 HashMap, TreeMap, ConcurrentHashMap 等類的父類。
1. AbstractMap.SimpleEntry<K, V>的結構：SimpleEntry<K, V>是維護鍵和值的 Entry。可以使用 setValue() 方法更改值。此類簡化了構建自定義映射實現的過程。例如，可以使用 Map.entrySet().toArray 方法方便地返回 SimpleEntry實例數組。
//AbstractMap內部類，實現Map.Entry接口
public static class SimpleEntry<K,V>
implements Entry<K,V>, java.io.Serializable
{
private static final long serialVersionUID = -8499721149061103585L;
private final K key;
private V value;
/**
創建一個項，它表示指定鍵到指定值得映射關係
*/
public SimpleEntry(K key, V value) {
this.key = key;
this.value = value;
}
/**
* Creates an entry representing the same mapping as the
* specified entry.
*
* @param entry the entry to copy
返回一個SimpleEntry,表示映射關係與指定的項相同
*/
public SimpleEntry(Entry<? extends K, ? extends V> entry) {
this.key = entry.getKey();
this.value = entry.getValue();
}
/**
* Returns the key corresponding to this entry.
*
* @return the key corresponding to this entry
返回此項的鍵
*/
public K getKey() {
return key;
}
/**
* Returns the value corresponding to this entry.
*
* @return the value corresponding to this entry
返回此項的值
*/
public V getValue() {
return value;
}
/**
* Replaces the value corresponding to this entry with the specified
* value.
*
* @param value new value to be stored in this entry
* @return the old value corresponding to the entry
用指定的值替換對應的值，並返回舊值。
*/
public V setValue(V value) {
V oldValue = this.value;
this.value = value;
return oldValue;
}
/**
判斷是否相等
*/
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());
}
/**
獲取hashCode
*/
public int hashCode() {
return (key == null ? 0 : key.hashCode()) ^
(value == null ? 0 : value.hashCode());
}
/**
返回String形式
*/
public String toString() {
return key + "=" + value;
}
}
AbstractMap.SimpleImmutableEntry<K,V>的結構
SimpleImmutableEntry<K,V>是維護不可變的鍵和值的 Entry，不支持setValue()方法。方便用於在返回線程安全的鍵-值映射關係的方法
public static class SimpleImmutableEntry<K,V>
implements Entry<K,V>, java.io.Serializable
{
private static final long serialVersionUID = 7138329143949025153L;
private final K key;
private final V value;
/**
返回SimpleImmutableEntry，表示指定鍵到指定值得映射關係
*/
public SimpleImmutableEntry(K key, V value) {
this.key = key;
this.value = value;
}
/**
* 返回SimpleImmutableEntry，表示映射關係與指定項相同
*/
public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) {
this.key = entry.getKey();
this.value = entry.getValue();
}
/**
* Returns the key corresponding to this entry.
*
* @return the key corresponding to this entry
返回指定的鍵
*/
public K getKey() {
return key;
}
/**
* Returns the value corresponding to this entry.
*
* @return the value corresponding to this entry
返回指定的值
*/
public V getValue() {
return value;
}
/**
* Replaces the value corresponding to this entry with the specified
* value (optional operation). This implementation simply throws
* {@code UnsupportedOperationException}, as this class implements
* an <i>immutable</i> map entry.
*
* @param value new value to be stored in this entry
* @return (Does not return)
* @throws UnsupportedOperationException always
該方法僅拋出UnsupportedOperationException，表明該Entry不支持setValue方法
*/
public V setValue(V value) {
throw new UnsupportedOperationException();
}
/**
比較指定對象與O的相等性
*/
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());
}
/**
返回此映射項的哈希值:key值的哈希碼與value值的哈希碼按位異或的結果
*/
public int hashCode() {
return (key == null ? 0 : key.hashCode()) ^
(value == null ? 0 : value.hashCode());
}
/**
* Returns a String representation of this map entry. This
* implementation returns the string representation of this
* entry's key followed by the equals character ("{@code =}")
* followed by the string representation of this entry's value.
*
* @return a String representation of this map entry
*/
public String toString() {
return key + "=" + value;
}
}
AbstractMap
AbstractMap類提供 Map接口的骨幹實現，以最大限度地減少實現此接口所需的工作。
要實現不可修改的映射，編程人員只需擴展此類並提供 entrySet() 方法的實現即可，該方法將返回映射的映射關係 set視圖。通常，返回的 set 將依次在 AbstractSet 上實現。此 set不支持 add() 或 remove() 方法，其迭代器也不支持 remove() 方法。
要實現可修改的映射，編程人員必須另外重寫此類的put() 方法（否則將拋出 UnsupportedOperationException），entrySet().iterator() 返回的迭代器也必須另外實現其 remove() 方法
/**
構造函數
*/
protected AbstractMap() {
}
// Query Operations
/**
返回k-v的數量
*/
public int size() {
return entrySet().size();
}
/**
* {@inheritDoc}
*
* @implSpec
* This implementation returns {@code size() == 0}.
未包含k-v，則返回true
*/
public boolean isEmpty() {
return size() == 0;
}
/**
鍵值對<key,value>集合中包含指定的value值,則返回ture
*/
public boolean containsValue(Object value) {
//entrySet()返回此映射中包含的映射關係Set視圖
Iterator<Entry<K,V>> i = entrySet().iterator();
//map集合允許value爲null,故分兩種情況處理
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;
}
/**
鍵值對<key,value>集合中包含指定的key值,則返回ture
*/
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;
}
/**
返回指定鍵所映射的值；如果此映射不包含該鍵的映射關係，則返回 null
*/
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
/**
添加指定的k-v映射關係
*/
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
/**
如果存在一個鍵的映射關係，則將其從此映射中移除。並返回以前與key關聯的值；如果沒有key的映射關係，則返回null
注意，如果 entrySet()返回的集合所調用的迭代器不支持 remove方法，並且此映射包含指定鍵的映射關係，則此實現將拋出 UnsupportedOperationException。
*/
public V remove(Object key) {
Iterator<Entry<K,V>> i = entrySet().iterator();
Entry<K,V> correctEntry = null;//用於指向給定鍵值對應的映射關係
//找到指定鍵的映射關係，並賦值給correctEntry
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();//得到以前與key關聯的值
i.remove();/運用迭代器中的remove()方法來對得到的鍵值對項進行移除工作
}
return oldValue;
}
// Bulk Operations
/**
從指定Map中將所有映射關係<key,value>複製到此映射中
*/
public void putAll(Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
put(e.getKey(), e.getValue());
}
/**
清除所有映射關係
*/
public void clear() {
entrySet().clear();
}
// Views
/**
Map中key值的唯一性決定鍵值集合的視圖類型爲Set
Map中value值的可重複性決定值集合的視圖類型爲Collection
*/
transient Set<K> keySet;
transient Collection<V> values;
/**
返回此映射中包含的鍵的Set視圖
*/
public Set<K> keySet() {
Set<K> ks = keySet;
if (ks == null) {
ks = 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 isEmpty() {
return AbstractMap.this.isEmpty();
}
public void clear() {
AbstractMap.this.clear();
}
public boolean contains(Object k) {
return AbstractMap.this.containsKey(k);
}
};
keySet = ks;
}
return ks;
}
/**
返回此映射中包含的值的 Collection視圖
*/
public Collection<V> values() {
Collection<V> vals = values;
if (vals == null) {
vals = 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 isEmpty() {
return AbstractMap.this.isEmpty();
}
public void clear() {
AbstractMap.this.clear();
}
public boolean contains(Object v) {
return AbstractMap.this.containsValue(v);
}
};
values = vals;
}
return vals;
}
//返回此映射中包含的映射關係的Set視圖
public abstract Set<Entry<K,V>> entrySet();
// Comparison and hashing
/**
比較指定對象與此映射的相等性
*/
public boolean equals(Object o) {
//如果給定對象也是一個映射並且兩個映射表示相同的映射關係，則返回true
if (o == this)
return true;
//檢查指定的對象是否爲映射關係
if (!(o instanceof Map))
return false;
Map<?,?> m = (Map<?,?>) o;
//檢查指定的對象是否是一個大小與此映射相等的映射
if (m.size() != size())
return false;
//在此映射 entrySet()返回的collection上進行迭代，並檢查指定的映射是否包含此映射所包含的每個映射關係
try {
for (Entry<K, V> e : entrySet()) {
K key = e.getKey();
V value = e.getValue();
if (value == null) {
if (!(m.get(key) == null && m.containsKey(key)))
return false;
} else {
if (!value.equals(m.get(key)))
return false;
}
}
} catch (ClassCastException unused) {
return false;
} catch (NullPointerException unused) {
return false;
}
return true;
}
/**
返回此映射的哈希值
*/
public int hashCode() {
int h = 0;
for (Entry<K, V> entry : entrySet())
h += entry.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 {@code entrySet} view's iterator, enclosed in braces
* ({@code "{}"}). Adjacent mappings are separated by the characters
* {@code ", "} (comma and space). Each key-value mapping is rendered as
* the key followed by an equals sign ({@code "="}) followed by the
* associated value. Keys and values are converted to strings as by
* {@link String#valueOf(Object)}.
*
* @return a string representation of this map
*/
public String toString() {
Iterator<Entry<K,V>> i = entrySet().iterator();
if (! i.hasNext())
return "{}";
StringBuilder sb = new StringBuilder();
sb.append('{');
for (;;) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
sb.append(key == this ? "(this Map)" : key);
sb.append('=');
sb.append(value == this ? "(this Map)" : value);
if (! i.hasNext())
return sb.append('}').toString();
sb.append(',').append(' ');
}
}
/**
返回此 AbstractMap 實例的淺表副本：不復制鍵和值本身
*/
protected Object clone() throws CloneNotSupportedException {
AbstractMap<?,?> result = (AbstractMap<?,?>)super.clone();
result.keySet = null;
result.values = null;
return result;
}
/**
比較是否相等，及是否爲null
*/
private static boolean eq(Object o1, Object o2) {
return o1 == null ? o2 == null : o1.equals(o2);
}