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Initialize HashMap in Java

Here is our sample Java program to create and initialize the HashMap in the same line. In this example, we have used the double brace initialization idiom to initialize both static and non-static HashMap. In following example a map with several entries is initialized. This factory method supports a maximum of 10 key-value pairs and requires at least Java 9. The Map interface defines an object that maps keys to values.

This post will discuss various methods to initialize a map in Java. The HashMap class uses a hashtable to implement the Map interface. This allows the execution time of basic operations, such as get and put, to remain constant even for large sets.

It is used to initializes the hash map by using the elements of the given Map object map. It is used to create an empty HashMap object with specified initial capacity as well as load factor. Note that all of these Map.of… methods return a Map of an unspecified class. The underlying concrete class may even vary from one version of Java to another.

In the example above, we are using the asList() method to create a List of key-value pairs. The asList() method is a static method of the Arrays class in Java that returns a List. We are then using the put() method to add three key-value pairs to the map. You can add multiple key-value pairs to the HashMap by calling the put() method multiple times.

HashMap is a Java Collections framework that provides HashTable for implementing the Map interface. HashMap implementation is similar to HashTable which is one of the data structures. Similar to HashTable which implements using pairs HashMap also uses these pairs. This article describes the need to initialize a HashMap with fitting default values.

It is used to create an empty HashMap object with specified initial capacity under default load factor 0.75. The map is immutable, so you cannot add or remove entries after instantiating. Also, the key carter’s brewing and the value of each entry is immutable, cannot be changed. See the Javadoc for other rules, such as no NULLs allowed, no duplicate keys allowed, and the iteration order of mappings is arbitrary.

Please use our online compiler to post code in comments using C, C++, Java, Python, JavaScript, C#, PHP, and many more popular programming languages. Following is the list of constructors supported by the HashMap class. I found a great article by baeldung that lists several ways to do this in different Java versions. Also, if a key appears several times, the default Collectors.toMap will throw an IllegalStateException. ImmutableMap is not the same as a HashMap, as it will fail on null values, whereas map HashMap will not. This won’t work if you want to initial the elements in a function…