How to work with Java HashMap

#java #hashmap

In the tutorial, JavaSampleApproach will introduce you how to work with Java HashMap

I. Concepts

Java HashMap is a construction of Map interface, so it provides all methods of Map interface.
Related post: How to work with Java Map Interface

It permits a null key and null values HashMap provides 3 Constructors:
HashMap(): default initial capacity (16) and the default load factor (0.75).
HashMap(int initialCapacity, float loadFactor)
HashMap(Map<? extends K,? extends V> m): constructs a new HashMap with the same mappings as the specified Map. Note: In common case, we use empty constructor HashMap() & HashMap(Map<? extends K,? extends V> m) constructors. Example:
```
//a void (no arguments) constructor
Map map = new HashMap();
```

//a constructor with a single argument of type Map
Map newMap = new HashMap(map);

For insert and retrieve a key-value mapping, we uses: put() & get() methods.