How do you implement a Map with multiple keys?

1. class Main. { public static void main(String[] args)
2. { // Create a map. Map, String> listKeyMap = Maps. newHashMap();
3. listKeyMap. put(ImmutableList. of(“key1”, “key2”), “value1”); // [key3, key4] -> value2. listKeyMap. put(ImmutableList. of(“key3”, “key4”), “value2”);

Can Map have multiple same keys?

However, none of the existing Java core Map implementations allow a Map to handle multiple values for a single key. As we can see, if we try to insert two values for the same key, the second value will be stored, while the first one will be dropped. isEqualTo(null); assertThat(map. put(“key1”, “value2”)).

How do I store multiple values on a Map?

21 Answers

1. Use a map that has a list as the value. Map> .
2. Create a new wrapper class and place instances of this wrapper in the map. Map .
3. Use a tuple like class (saves creating lots of wrappers). Map> .
4. Use mulitple maps side-by-side.

Can HashMap have two keys?

You can’t have an hash map with multiple keys, but you can have an object that takes multiple parameters as the key.

How do you add multiple values in Java?

Add Multiple Items to an Java ArrayList

1. List anotherList = Arrays. asList(5, 12, 9, 3, 15, 88); list.
2. List list = new ArrayList<>(); Collections. addAll(list, 1, 2, 3, 4, 5);
3. List list = new ArrayList<>(); Integer[] otherList = new Integer[] {1, 2, 3, 4, 5}; Collections.

How can I store multiple values in one key HashMap?

How to add multiple values per key to a Java HashMap

1. Stick with the standard APIs and add a collection class like a ‘Vector’ or ‘ArrayList’ to your map or set.
2. Use the MultiMap and MultiValueMap classes from the Apache Commons library.

How to implement a map with multiple keys in Java?

Implement a Map with multiple keys (MultiKeyMap) in Java – Techie Delight This post will implement MultiKeyMap in plain Java and cover its possible implementations in Apache Commons Collection and Guava library. TECHIE DELIGHT </> Ace your Coding Interview FAANG Interview Preparation Data Structures

Can you create a hash map with multiple keys?

You can’t have an hash map with multiple keys, but you can have an object that takes multiple parameters as the key. Create an object called Index that takes an x and y value.

How to create a table with two keys?

Table represents a special map where two keys can be specified in combined fashion to refer to a single value. It is similar to creating a map of maps.

How to store multiple values under the same key?

If you call put (K, V) twice, with the same key but different values, the multimap contains mappings from the key to both values. I use Map for associating multiple values with a key in a Map. This way, I can store multiple values of different types associated with a key.

How do you implement a map with multiple keys?

1. class Main. { public static void main(String[] args)
2. { // Create a map. Map, String> listKeyMap = Maps. newHashMap();
3. listKeyMap. put(ImmutableList. of(“key1”, “key2”), “value1”); // [key3, key4] -> value2. listKeyMap. put(ImmutableList. of(“key3”, “key4”), “value2”);

Will map allow duplicate keys in Salesforce?

Features of Map KEY can’t be duplicate like SET. VALUE can be duplicate like LIST. We can have keys or values of any data type (eg: string, integer, etc).

How can I add multiple values in one HashMap key?

How to add multiple values per key to a Java HashMap

1. Stick with the standard APIs and add a collection class like a ‘Vector’ or ‘ArrayList’ to your map or set.
2. Use the MultiMap and MultiValueMap classes from the Apache Commons library.

Can a Map have duplicate keys?

Duplicate keys are not allowed in a Map. Basically, Map Interface has two implementation classes HashMap and TreeMap the main difference is TreeMap maintains an order of the objects but HashMap will not. HashMap allows null values and null keys. Both HashSet and HashMap are not synchronized.

Can a Map have duplicate keys C++?

STL map does not allow same Keys to be used. You may want to go for multi-map for that. a map will not throw any compile/run time error while inserting value using duplicate key. but while inserting, using the duplicate key it will not insert a new value, it will return the same exiting value only.

Does javascript Map allow duplicate keys?

Map Keys. Maps accept any data type as a key, and do not allow duplicate key values.

Can a map contain duplicate keys in Java?

A Map cannot contain duplicate keys and each key can map to at most one value. Some implementations allow null key and null value like the HashMap and LinkedHashMap, but some do not like the TreeMap. The order of a map depends on the specific implementations.

Can a compound key be used with multiple keys?

Taken one step further from simple keys are concatenated or compound keys. As the name implies, a concatenated key is a joining of multiple single keys. For example, the system may automatically combine the last_name and year_of_birth single keys into a concatenated key, like so: smith1980.

Which is an example of a key value mapping?

Maps are perfect to use for key-value association mapping such as dictionaries. The maps are used to perform lookups by keys or when someone wants to retrieve and update elements by keys. Some examples are: A map of error codes and their descriptions. A map of zip codes and cities. A map of managers and employees.

Is it possible to have multiple candidate keys in a table?

It is possible for a table to have multiple candidate keys, which effectively behave similar to a primary key in that a candidate key is unique, NOT NULL, and is a singular representation of that table record.