HashMap class Methods in Java

java.util.HashMap

Hash table-based implementation of the Map interface.

Some methods of HashMap class.

clear(): This method removes all of the mappings from this map.

clone(): This method returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.

compute(K, BiFunction): This method attempts to compute a mapping for the specified key and its current mapped value

computeIfAbsent(K, Function): If the specified key is not already associated with a value attempt to compute its value using the given mappingfunction and enter it into this map unless null.

computeIfPresent(K, BiFunction): f 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.

containsKey(Object): This method returns true if this map contains a mapping for the specified key.

containsValue(Object): This method returns true if this map maps one or more keys to the specified value.

entrySet(): This method returns a Set view of the mappings contained in this map.

equals(Object): This method compares the specified object with this map for equality. 

forEach(BiConsumer): This method performs the given action for each entry in this map until all entries have been processed or the action throws an exception.

get(Object): This method returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

getOrDefault(Object, V): This method returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.

hashCode(): This method returns the hash code value for this map.

isEmpty(): This method returns true if this map contains no key-value mappings.

keySet(): This method returns a Set view of the keys contained in this map.

merge(K, V, BiFunction): If the specified key is not already associated with a value or is associated with null, associate it with the given non-null value.

put(K, V): This method associates the specified value with the specified key in this map.

putAll(Map): This method copies all of the mappings from the specified map to this map.

putIfAbsent(K, V): If the specified key is not already associated with a value associates it with the given value and returns null, else returns the current value.

remove(Object): This method removes the mapping for the specified key from this map if present.

remove(Object, Object): This method removes the entry for the specified key only if it is currently mapped to the specified value.

replace(K, V): This method replaces the entry for the specified key only if it is currently mapped to some value.

replace(K, V, V): This method replaces the entry for the specified key only if currently mapped to the specified value.

replaceAll(BiFunction): This method 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.

size(): This method returns the number of key-value mappings in this map.

values(): This method returns a Collection view of the values contained in this map.