java.util.Map Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.util;
/**
* A {@code Map} is a data structure consisting of a set of keys and values
* in which each key is mapped to a single value. The class of the objects
* used as keys is declared when the {@code Map} is declared, as is the
* class of the corresponding values.
*
* A {@code Map} provides helper methods to iterate through all of the
* keys contained in it, as well as various methods to access and update
* the key/value pairs.
*/
public interface Map {
/**
* {@code Map.Entry} is a key/value mapping contained in a {@code Map}.
*/
public static interface Entry {
/**
* Compares the specified object to this {@code Map.Entry} and returns if they
* are equal. To be equal, the object must be an instance of {@code Map.Entry} and have the
* same key and value.
*
* @param object
* the {@code Object} to compare with this {@code Object}.
* @return {@code true} if the specified {@code Object} is equal to this
* {@code Map.Entry}, {@code false} otherwise.
* @see #hashCode()
*/
public boolean equals(Object object);
/**
* Returns the key.
*
* @return the key
*/
public K getKey();
/**
* Returns the value.
*
* @return the value
*/
public V getValue();
/**
* Returns an integer hash code for the receiver. {@code Object} which are
* equal return the same value for this method.
*
* @return the receiver's hash code.
* @see #equals(Object)
*/
public int hashCode();
/**
* Sets the value of this entry to the specified value, replacing any
* existing value.
*
* @param object
* the new value to set.
* @return object the replaced value of this entry.
*/
public V setValue(V object);
};
/**
* Removes all elements from this {@code Map}, leaving it empty.
*
* @throws UnsupportedOperationException
* if removing elements from this {@code Map} is not supported.
* @see #isEmpty()
* @see #size()
*/
public void clear();
/**
* Returns whether this {@code Map} contains the specified key.
*
* @param key
* the key to search for.
* @return {@code true} if this map contains the specified key,
* {@code false} otherwise.
*/
public boolean containsKey(Object key);
/**
* Returns whether this {@code Map} contains the specified value.
*
* @param value
* the value to search for.
* @return {@code true} if this map contains the specified value,
* {@code false} otherwise.
*/
public boolean containsValue(Object value);
/**
* Returns a {@code Set} containing all of the mappings in this {@code Map}. Each mapping is
* an instance of {@link Map.Entry}. As the {@code Set} is backed by this {@code Map},
* changes in one will be reflected in the other.
*
* @return a set of the mappings
*/
public Set> entrySet();
/**
* Compares the argument to the receiver, and returns {@code true} if the
* specified object is a {@code Map} and both {@code Map}s contain the same mappings.
*
* @param object
* the {@code Object} to compare with this {@code Object}.
* @return boolean {@code true} if the {@code Object} is the same as this {@code Object}
* {@code false} if it is different from this {@code Object}.
* @see #hashCode()
* @see #entrySet()
*/
public boolean equals(Object object);
/**
* Returns the value of the mapping with the specified key.
*
* @param key
* the key.
* @return the value of the mapping with the specified key, or {@code null}
* if no mapping for the specified key is found.
*/
public V get(Object key);
/**
* Returns an integer hash code for the receiver. {@code Object}s which are equal
* return the same value for this method.
*
* @return the receiver's hash.
* @see #equals(Object)
*/
public int hashCode();
/**
* Returns whether this map is empty.
*
* @return {@code true} if this map has no elements, {@code false}
* otherwise.
* @see #size()
*/
public boolean isEmpty();
/**
* Returns a set of the keys contained in this {@code Map}. The {@code Set} is backed by
* this {@code Map} so changes to one are reflected by the other. The {@code Set} does not
* support adding.
*
* @return a set of the keys.
*/
public Set keySet();
/**
* Maps the specified key to the specified value.
*
* @param key
* the key.
* @param value
* the value.
* @return the value of any previous mapping with the specified key or
* {@code null} if there was no mapping.
* @throws UnsupportedOperationException
* if adding to this {@code Map} is not supported.
* @throws ClassCastException
* if the class of the key or value is inappropriate for
* this {@code Map}.
* @throws IllegalArgumentException
* if the key or value cannot be added to this {@code Map}.
* @throws NullPointerException
* if the key or value is {@code null} and this {@code Map} does
* not support {@code null} keys or values.
*/
public V put(K key, V value);
/**
* Copies every mapping in the specified {@code Map} to this {@code Map}.
*
* @param map
* the {@code Map} to copy mappings from.
* @throws UnsupportedOperationException
* if adding to this {@code Map} is not supported.
* @throws ClassCastException
* if the class of a key or a value of the specified {@code Map} is
* inappropriate for this {@code Map}.
* @throws IllegalArgumentException
* if a key or value cannot be added to this {@code Map}.
* @throws NullPointerException
* if a key or value is {@code null} and this {@code Map} does not
* support {@code null} keys or values.
*/
public void putAll(Map map);
/**
* Removes a mapping with the specified key from this {@code Map}.
*
* @param key
* the key of the mapping to remove.
* @return the value of the removed mapping or {@code null} if no mapping
* for the specified key was found.
* @throws UnsupportedOperationException
* if removing from this {@code Map} is not supported.
*/
public V remove(Object key);
/**
* Returns the number of mappings in this {@code Map}.
*
* @return the number of mappings in this {@code Map}.
*/
public int size();
/**
* Returns a {@code Collection} of the values contained in this {@code Map}. The {@code Collection}
* is backed by this {@code Map} so changes to one are reflected by the other. The
* {@code Collection} supports {@link Collection#remove}, {@link Collection#removeAll},
* {@link Collection#retainAll}, and {@link Collection#clear} operations,
* and it does not support {@link Collection#add} or {@link Collection#addAll} operations.
*
* This method returns a {@code Collection} which is the subclass of
* {@link AbstractCollection}. The {@link AbstractCollection#iterator} method of this subclass returns a
* "wrapper object" over the iterator of this {@code Map}'s {@link #entrySet()}. The {@link AbstractCollection#size} method
* wraps this {@code Map}'s {@link #size} method and the {@link AbstractCollection#contains} method wraps this {@code Map}'s
* {@link #containsValue} method.
*
* The collection is created when this method is called at first time and
* returned in response to all subsequent calls. This method may return
* different Collection when multiple calls to this method, since it has no
* synchronization performed.
*
* @return a collection of the values contained in this map.
*/
public Collection values();
default V putIfAbsent(K key, V value) {
V v = get(key);
if (v == null) {
v = put(key, value);
}
return v;
}
}