More Java collections – meet the Java HashMap
The Java HashMap is neat. It's part of the Java collections framework and a kind of cousin of the ArrayList class that we will use in the Note to Self project in the next chapter. They basically encapsulate useful data storage techniques that would otherwise be quite technical for us to code successfully for ourselves.
I thought it would be worth taking a first look at HashMap on its own. Suppose we want to store the data of lots of characters from a role-playing game and each different character is represented by an object of type Character.
We could use some of the Java tools we already know about, such as arrays or ArrayList. The Java HashMap is also like these things, but with HashMap we can give a unique key/identifier to each Character object and access any such object using that key/identifier.
The term hash comes from the process of turning our chosen key/identifier into something used internally by the HashMap...