What is HashMap

Answer 1

In a Hashtable, instead of accessing elements with an index number (like in arrays for example), you access them with their key (which can be a number, a string, etc.).

For example, here we create a new Hashtable dictionary, insert the key/value pair "blanc"/"white", and display the item with key "blanc":
Hashtable dictionary = new Hashtable();
dictionary.put("blanc", "white");
System.out.println(dictionary.get("blanc"));

A HashMap is almost like a Hashtable, the only differences being that it accepts null as value or key, and it is not thread-safe.

Answer 2

just like an ArrayList but instead of indexing elements using Integers , You can use e.g Strings or other types ...

e.g.

HashMap hm=new HashMap<String,String>();

Answer 3

Hashtable? What's that?