HashMap | Notion

Modifier and Type	Method and Description
`void`	[`clear](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#clear--)()`Removes all of the mappings from this map.
`Object`	[`clone](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#clone--)()`Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.
`V`	[compute](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#compute-K-java.util.function.BiFunction-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [BiFunction](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> remappingFunction)Attempts to compute a mapping for the specified key and its current mapped value (or `null` if there is no current mapping).
`V`	[`computeIfAbsent](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#computeIfAbsent-K-java.util.function.Function-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [Function](https://docs.oracle.com/javase/8/docs/api/java/util/function/Function.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> mappingFunction)`If the specified key is not already associated with a value (or is mapped to `null`), attempts to compute its value using the given mapping function and enters it into this map unless `null`.
`V`	[computeIfPresent](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#computeIfPresent-K-java.util.function.BiFunction-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [BiFunction](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> remappingFunction)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.
`boolean`	[`containsKey](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#containsKey-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key)`Returns true if this map contains a mapping for the specified key.
`boolean`	[`containsValue](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#containsValue-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) value)`Returns true if this map maps one or more keys to the specified value.
[`Set](https://docs.oracle.com/javase/8/docs/api/java/util/Set.html)<[Map.Entry](https://docs.oracle.com/javase/8/docs/api/java/util/Map.Entry.html)<[K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),[V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)>>`	[`entrySet](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#entrySet--)()`Returns a `Set` view of the mappings contained in this map.
`void`	[`forEach](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#forEach-java.util.function.BiConsumer-)([BiConsumer](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiConsumer.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> action)`Performs the given action for each entry in this map until all entries have been processed or the action throws an exception.
`V`	[`get](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#get-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key)`Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key.
`V`	[`getOrDefault](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#getOrDefault-java.lang.Object-V-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) defaultValue)`Returns the value to which the specified key is mapped, or `defaultValue` if this map contains no mapping for the key.
`boolean`	[`isEmpty](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#isEmpty--)()`Returns true if this map contains no key-value mappings.
[`Set](https://docs.oracle.com/javase/8/docs/api/java/util/Set.html)<[K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)>`	[`keySet](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#keySet--)()`Returns a `Set` view of the keys contained in this map.
`V`	[merge](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#merge-K-V-java.util.function.BiFunction-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) value, [BiFunction](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html)<? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> remappingFunction)If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.
`V`	[`put](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#put-K-V-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) value)`Associates the specified value with the specified key in this map.
`void`	[`putAll](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#putAll-java.util.Map-)([Map](https://docs.oracle.com/javase/8/docs/api/java/util/Map.html)<? extends [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> m)`Copies all of the mappings from the specified map to this map.
`V`	[`putIfAbsent](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#putIfAbsent-K-V-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) value)`If the specified key is not already associated with a value (or is mapped to `null`) associates it with the given value and returns `null`, else returns the current value.
`V`	[`remove](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#remove-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key)`Removes the mapping for the specified key from this map if present.
`boolean`	[`remove](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#remove-java.lang.Object-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key, [Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) value)`Removes the entry for the specified key only if it is currently mapped to the specified value.
`V`	[`replace](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#replace-K-V-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) value)`Replaces the entry for the specified key only if it is currently mapped to some value.
`boolean`	[`replace](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#replace-K-V-V-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) oldValue, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) newValue)`Replaces the entry for the specified key only if currently mapped to the specified value.
`void`	[`replaceAll](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#replaceAll-java.util.function.BiFunction-)([BiFunction](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> function)`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.
`int`	[`size](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#size--)()`Returns the number of key-value mappings in this map.
[`Collection](https://docs.oracle.com/javase/8/docs/api/java/util/Collection.html)<[V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)>`	[`values](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#values--)()`Returns a `Collection` view of the values contained in this map.

Modifier and Type	Method and Description
`void`	[`clear](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#clear--)()`Removes all of the mappings from this map.
`Object`	[`clone](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#clone--)()`Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.
`V`	[compute](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#compute-K-java.util.function.BiFunction-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [BiFunction](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> remappingFunction)Attempts to compute a mapping for the specified key and its current mapped value (or `null` if there is no current mapping).
`V`	[`computeIfAbsent](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#computeIfAbsent-K-java.util.function.Function-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [Function](https://docs.oracle.com/javase/8/docs/api/java/util/function/Function.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> mappingFunction)`If the specified key is not already associated with a value (or is mapped to `null`), attempts to compute its value using the given mapping function and enters it into this map unless `null`.
`V`	[computeIfPresent](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#computeIfPresent-K-java.util.function.BiFunction-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [BiFunction](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> remappingFunction)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.
`boolean`	[`containsKey](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#containsKey-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key)`Returns true if this map contains a mapping for the specified key.
`boolean`	[`containsValue](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#containsValue-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) value)`Returns true if this map maps one or more keys to the specified value.
[`Set](https://docs.oracle.com/javase/8/docs/api/java/util/Set.html)<[Map.Entry](https://docs.oracle.com/javase/8/docs/api/java/util/Map.Entry.html)<[K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),[V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)>>`	[`entrySet](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#entrySet--)()`Returns a `Set` view of the mappings contained in this map.
`void`	[`forEach](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#forEach-java.util.function.BiConsumer-)([BiConsumer](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiConsumer.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> action)`Performs the given action for each entry in this map until all entries have been processed or the action throws an exception.
`V`	[`get](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#get-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key)`Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key.
`V`	[`getOrDefault](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#getOrDefault-java.lang.Object-V-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) defaultValue)`Returns the value to which the specified key is mapped, or `defaultValue` if this map contains no mapping for the key.
`boolean`	[`isEmpty](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#isEmpty--)()`Returns true if this map contains no key-value mappings.
[`Set](https://docs.oracle.com/javase/8/docs/api/java/util/Set.html)<[K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)>`	[`keySet](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#keySet--)()`Returns a `Set` view of the keys contained in this map.
`V`	[merge](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#merge-K-V-java.util.function.BiFunction-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) value, [BiFunction](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html)<? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> remappingFunction)If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.
`V`	[`put](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#put-K-V-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) value)`Associates the specified value with the specified key in this map.
`void`	[`putAll](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#putAll-java.util.Map-)([Map](https://docs.oracle.com/javase/8/docs/api/java/util/Map.html)<? extends [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> m)`Copies all of the mappings from the specified map to this map.
`V`	[`putIfAbsent](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#putIfAbsent-K-V-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) value)`If the specified key is not already associated with a value (or is mapped to `null`) associates it with the given value and returns `null`, else returns the current value.
`V`	[`remove](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#remove-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key)`Removes the mapping for the specified key from this map if present.
`boolean`	[`remove](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#remove-java.lang.Object-java.lang.Object-)([Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) key, [Object](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html) value)`Removes the entry for the specified key only if it is currently mapped to the specified value.
`V`	[`replace](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#replace-K-V-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) value)`Replaces the entry for the specified key only if it is currently mapped to some value.
`boolean`	[`replace](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#replace-K-V-V-)([K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) key, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) oldValue, [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html) newValue)`Replaces the entry for the specified key only if currently mapped to the specified value.
`void`	[`replaceAll](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#replaceAll-java.util.function.BiFunction-)([BiFunction](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html)<? super [K](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? super [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html),? extends [V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)> function)`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.
`int`	[`size](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#size--)()`Returns the number of key-value mappings in this map.
[`Collection](https://docs.oracle.com/javase/8/docs/api/java/util/Collection.html)<[V](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html)>`	[`values](https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#values--)()`Returns a `Collection` view of the values contained in this map.