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Understanding encapsulation

From: Java Essential Training

Video: Understanding encapsulation

The principles of object-oriented programming depend on a few basic concepts and one of the most important concepts is encapsulation. Encapsulation means that you're packaging complex functionality to make it easy to use. When you first create Java applications, most new programmers will put all of their code into the main method, and I've been doing that so far in this course. But you quickly find out as your applications get larger and gain features that putting all the code into one place makes that code very tough to manage.

Understanding encapsulation

The principles of object-oriented programming depend on a few basic concepts and one of the most important concepts is encapsulation. Encapsulation means that you're packaging complex functionality to make it easy to use. When you first create Java applications, most new programmers will put all of their code into the main method, and I've been doing that so far in this course. But you quickly find out as your applications get larger and gain features that putting all the code into one place makes that code very tough to manage.

So instead, you want to break the code out into individual classes, grouping the functionality, however, the logic dictates for your application. When you do this, you have some big advantages. One advantage is that you can restrict access, one part of the application might be able to use a particular function or another part of the application wouldn't be allowed. If you put all the code in one place, that's tough to restrict. When you break it apart, it's easier. Similarly, when you store data in a Java class, if you wrap it up as encapsulated data, you have the option of hiding how it's being stored.

You don't have to tell the user of the data, that is a programmer who's calling a particular class, whether that data is being stored as an array, a collection of some kind, or any other object. You simply provide methods that the user of that class can call and all the complexity is hidden. One way to think about encapsulation is to look at an analogy of the 3D world. Let's take an example of an industrial machine, in this case, an olive press. In order to use an olive press, if you were asked to know everything about how the press worked, it would be very difficult to get started.

If you had to know which direction each gear was going to turn, which order each of the pressing arms is going to come down, and how much oil might come out of each individual olive, it would be very difficult to get any work done at all. So most real industrial machines are encapsulated and that means that they wrap up their complexity in a big box and then you can simply add the olives in the case of an olive press, perhaps press a button and out comes the olive oil. It's much easier for a new user to understand how to use the olive press.

There is still complexity, there are still gears, there are still pressing arms, there are still calculations to be done, but the whole process of getting started with the machine is greatly simplified. Code-encapsulation works the same way. Let's take an example of non-encapsulated code. Again, if you're a new Java developer, you might be tempted to put all the code for the application in the main method of your primary class. In this example, I'm creating an array and then I'm creating instances of two other classes, and then I'm looping through the array and doing something with it.

This little bit of code might not look too daunting but imagine if the code had expanded so you had literally hundreds or thousands of lines of code all in one place. Then somebody comes along and says would you add a new feature to the application or I found a bug and it needs to be fixed. This sort of monolithic code is very, very difficult to manage. So in Java applications, you're encouraged from the beginning to break your applications down into small pieces. So for example, I may take some of that code and move it off into its own custom class.

I might create a class called OlivePress. Within the OlivePress class, I might declare a private field or a private variable. In this case, it's an array of olive objects named olives, and then I might have a constructor method that allows me to pass that data in as I create an instance of the class. Then I might have a method called getOil that can be called from anywhere in the application. This method would encapsulate the complexity of how you have to loop through the list of olives, crush them and add them to the olive oil.

The developer of this class needs to understand and deal with the complexity, but the user of the class only has to call the getOil method and so the primary code of the application can now be very brief and very easy to read. I would create an instance of the OlivePress, I'd pass in my olives, I'd call the getOil method and I get back the oil. All of the mechanics and the complexity of how the operation happened would be hidden from me. All I need to know is call the method, get the result.

So that's how encapsulation works. The benefits of encapsulation include that you can break your functionality down into small maintainable units. It's much easier to fix bugs when you're looking at a small amount of code and much more difficult when you're looking at a massive amount of code. So encapsulation helps you maintain the application over the long-term. You can also use encapsulation to group functionality and data together. In Java, as with most object-oriented languages, you can define classes that group the data and the functionality that manages that data together or you can create individual classes; one for the data, one for the functionality, and bind them together using a process called loose coupling.

And finally, all of this together means that you can test your software and maintain it over the long- term at a granular level. Rather than looking at your application as one huge block of code, you're breaking it down into small manageable pieces. So in the rest of this chapter, I'm going to talk about the mechanics of this in Java. How do you create your own custom classes? How do you move code from a monolithic application and break it down into smaller pieces? And how do you declare classes that serve as utility libraries or that are their own custom classes that can be instantiated and seen as data objects all on their own?

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This video is part of

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Java Essential Training

71 video lessons · 71735 viewers

David Gassner
Author

 
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  1. 10m 8s
    1. Welcome
      1m 3s
    2. Is this course for you?
      5m 35s
    3. Using the exercise files
      3m 30s
  2. 31m 24s
    1. The history of Java
      5m 19s
    2. Java compilation and syntax
      8m 54s
    3. Understanding the principles of Java
      8m 28s
    4. Choosing a development environment
      8m 43s
  3. 19m 5s
    1. Installing Java on Windows
      6m 42s
    2. Installing Eclipse on Windows
      3m 19s
    3. Exploring Java on Mac OS X Leopard and Snow Leopard
      2m 27s
    4. Installing Java on Mac OS X Lion
      3m 27s
    5. Installing Eclipse on Mac OS X
      3m 10s
  4. 46m 10s
    1. Creating a Hello World application
      11m 7s
    2. Exploring the Eclipse IDE
      8m 55s
    3. Compiling and running from the command line
      8m 2s
    4. Passing arguments to the application
      8m 17s
    5. Using the Java API documentation
      4m 5s
    6. Memory management and garbage collection
      5m 44s
  5. 58m 57s
    1. Everything is an object
      5m 59s
    2. Declaring and initializing variables
      9m 15s
    3. Working with numbers
      8m 32s
    4. Converting numeric values
      6m 40s
    5. Understanding operators
      7m 58s
    6. Working with character values
      5m 14s
    7. Working with boolean values
      5m 13s
    8. Outputting primitive values as strings
      5m 33s
    9. Creating a simple calculator application
      4m 33s
  6. 53m 40s
    1. Writing conditional code
      5m 35s
    2. Using the switch statement
      8m 50s
    3. Repeating code blocks with loops
      7m 35s
    4. Creating reusable code with methods
      6m 31s
    5. Declaring methods with arguments
      5m 41s
    6. Overloading method names with different signatures
      5m 53s
    7. Passing arguments by reference or by value
      5m 35s
    8. Creating a more complex calculator application
      8m 0s
  7. 20m 30s
    1. Using the String class
      5m 44s
    2. Building strings with StringBuilder
      3m 34s
    3. Parsing string values
      3m 19s
    4. Working with date values
      7m 53s
  8. 20m 44s
    1. Understanding compile-time vs. runtime errors
      4m 5s
    2. Handling exceptions with try/catch
      4m 55s
    3. Throwing exceptions in methods
      2m 50s
    4. Using the debugger
      8m 54s
  9. 32m 22s
    1. Using simple arrays
      4m 47s
    2. Using two-dimensional arrays
      6m 17s
    3. Managing resizable arrays with ArrayList
      7m 14s
    4. Managing unordered data with HashMap
      6m 5s
    5. Looping through collections with iterators
      7m 59s
  10. 52m 2s
    1. Understanding encapsulation
      5m 59s
    2. Creating and instantiating custom classes
      8m 8s
    3. Organizing classes with packages
      6m 47s
    4. Creating and using instance methods
      6m 52s
    5. Storing data in instance variables
      6m 56s
    6. Using constructor methods
      5m 40s
    7. Managing instance data with getter and setter methods
      8m 26s
    8. Using class variables and Enum classes
      3m 14s
  11. 41m 15s
    1. Understanding inheritance and polymorphism
      9m 12s
    2. Extending custom classes
      9m 1s
    3. Overriding superclass methods
      3m 8s
    4. Casting subclass objects
      5m 3s
    5. Understanding interfaces and implementing classes
      4m 2s
    6. Creating your own interfaces
      4m 14s
    7. Using abstract classes and methods
      6m 35s
  12. 32m 17s
    1. Managing files with the core class library
      7m 46s
    2. Managing files with Apache Commons FileUtils
      7m 32s
    3. Reading a text file from a networked resource
      7m 52s
    4. Parsing an XML file with DOM
      9m 7s
  13. 17m 39s
    1. Creating your own JAR files
      4m 54s
    2. Understanding the classpath
      5m 2s
    3. Documenting code with Javadoc
      7m 43s
  14. 47s
    1. Goodbye
      47s

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