Book Image

Introduction to Programming

By : Nick Samoylov
Book Image

Introduction to Programming

By: Nick Samoylov

Overview of this book

Have you ever thought about making your computer do what you want it to do? Do you want to learn to program, but just don't know where to start? Instead of guiding you in the right direction, have other learning resources got you confused with over-explanations? Don't worry. Look no further. Introduction to Programming is here to help. Written by an industry expert who understands the challenges faced by those from a non-programming background, this book takes a gentle, hand-holding approach to introducing you to the world of programming. Beginning with an introduction to what programming is, you'll go on to learn about languages, their syntax, and development environments. With plenty of examples for you to code alongside reading, the book's practical approach will help you to grasp everything it has to offer. More importantly, you'll understand several aspects of application development. As a result, you'll have your very own application running by the end of the book. To help you comprehensively understand Java programming, there are exercises at the end of each chapter to keep things interesting and encourage you to add your own personal touch to the code and, ultimately, your application.
Table of Contents (21 chapters)

Map – HashMap stores/retrieves objects by key

The Map interface itself is not related to the Collection interface directly, but it uses the Set interface for its keys and Collection for its values. For example, for Map<Integer, String> map:

  • Set<Integer> keys = map.keySet();
  • Collection<String> values = map.values();

Each value is stored in a map with a unique key that is passed in along with the value when added to the map. In the case of Map<Integer, String> map:

map.put(42, "whatever");        //42 is the key for the value "whatever"

Then later, the value can be retrieved by its key:

String v = map.get(42);
System.out.println(v); //prints: whatever

These are the basic map operations that convey the Map interface's purpose – to provide a storage for key-value pairs, where both—key and valueare...