Flash cards
Review the key moves
1/3
Core idea
What is the main idea behind Java HashMap Methods?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
1Quick choice
Which statement best captures the main point of this lesson?
2Order
Put the learning moves in the order that makes the concept easiest to apply.
Some methods use the type of the HashMap's entries as a parameter or return value.
A list of all HashMap methods can be found in the table below.
All HashMap Methods
All HashMap Methods
A list of all HashMap methods can be found in the table below.
Some methods use the type of the HashMap's entries as a parameter or return value. The type of the key will be referred to as K and the type of the value will be referred to as V in the table.
| Method | Description | Return Type | |
|---|---|---|---|
| clear() | Remove all entries from the map. | void | |
| clone() | Create a copy of the HashMap. | Object | |
| compute() | Compute a value for an entry based on its key and the current value (if it has one) | V | |
| computeIfAbsent() | Compute a value for an entry based on its key only if an entry using the key does not already exist | V | |
| computeIfPresent() | Compute a new value for an entry based on its key and current value but only if an entry with the key already exists | V | |
| containsKey() | Indicate if an entry with the specified key exists in the map | boolean | |
| containsValue() | Indicate if an entry with the specified value exists in the map | boolean | |
| entrySet() | Return a set of all entries in the map | Set< Map.Entry<K,V> > | |
| forEach() | Perform an action on every entry in the map | void | |
| get() | Return the value of the entry with a specified key | V | |
| getOrDefault() | Return the value of the entry with a specified key or a default value if the entry is not found | V | |
| isEmpty() | Indicate whether the map is empty | boolean | |
| keySet() | Return a set of all keys in the map | Set< K > | |
| merge() | Compute a value for an entry based on its key and value or write a specific value if the entry does not yet exist | V | |
| put() | Write an entry into the map | V | |
| putAll() | Write all of the entries from another map into this one | void | |
| putIfAbsent() | Write an entry into the map but only if an entry with the same key does not already exist | V | |
| remove() | Remove an entry from the map | V | boolean |
| replace() | Write to an entry in the map only if it exists | V | boolean |
| replaceAll() | Replaces the value of every entry with the result of an operation | void | |
| size() | Return the number of entries in the map | int | |
| values() | Return a collection containing all of the values in the map | Collection< V > |