Simple Refactoring: Creating a New Class

[MUSIC] 0:00 Have you ever heard the old Boy Scout rule always leave the campground cleaner than 0:04 you found it? 0:08 As software developers we want to adopt this similar rule. 0:09 Every time we make a change to our code or someone else's code we want to try and 0:12 clean it up or improve it in some way. 0:16 We don't necessarily want to make any big changes. 0:19 But if we see an opportunity to, let's say use a variable, 0:21 instead of a hard-coded value, then we should make and test that change. 0:25 The important thing to emphasize here, 0:29 is that we don't want to change the behavior of the code. 0:31 We're just looking for opportunities to make it a little cleaner and 0:34 maybe more efficient. 0:37 Or maybe more maintainable for someone else to work with in the future. 0:38 This process is known as refactoring. 0:42 Let's see how we can do some refactoring with our fun fact code. 0:44 Right now, we have all of our code in this fun facts activity class. 0:48 And it works fine. 0:53 But what if we want to add a new activity that 0:55 also randomly selected one of our fun facts? 0:57 We could copy all of this code and add it to the new activity. 1:00 But then we would have the same code doing the same thing in two different places. 1:04 Then if we change this code for 1:09 some reason we'd have to remember to make this same change in the other activity. 1:11 This violates a core principle of software development. 1:16 The don't repeat yourself principle. 1:19 A better solution is to move the code that is repeated to a reusable component. 1:21 In this case, that can be a new object that can be used in multiple activities. 1:26 We learned before that activities are used to control how things work on the screen. 1:30 Our code does that, but 1:35 it also controls how the factors generated behind the scenes. 1:36 Let's make an object that separates out fact to generation. 1:40 Not only will it make our code a little cleaner, but 1:44 it will also prevent us from repeating ourselves in code. 1:47 It's another good programming practice to give each class a single responsibility. 1:51 So in our case, 1:55 the fun facts activity class will handle only how the screen looks and works. 1:56 And then new object, which we'll call fact book, will only 2:01 handle things about the facts themselves like how they are stored and selected. 2:04 This is another programming principle known as the single 2:09 responsibility principle. 2:11 All right, let me open up the project pane and then create our new fact book object. 2:13 There are a couple ways to do this. 2:18 We can go File, New and then pick Java Class, or 2:20 we can right click on our package and select new Java class. 2:29 I'll choose this option. 2:35 Then for the name, let's type FactBook. 2:36 And since we're making a normal class, we can leave this as is and click OK. 2:41 And here's our new file. 2:47 If we look over to the project pane, 2:49 we can see that a new FactBook file has been added to our package. 2:51 And our package now has two classes in it. 2:54 Also, at the top of our class, Android Studio has added a comment for us. 2:57 I'm not a big fan of this automatic comment, but luckily, 3:02 we can change a preference to make this not happen in the future. 3:05 Follow along if you'd like. 3:08 I'm going to click on Android Studio and then open the Preferences window. 3:10 Then expand Editor and select File and 3:17 Code Templates and over on the Includes tab select File Header. 3:22 And then delete everything in the window on the right, and hit OK. 3:28 We still need to delete this comment by hand though. 3:35 This class will be the blueprint for our FactBook object. 3:44 Remember that an object has two main components. 3:48 Fields or Member Variables which are properties about the object, 3:52 as well as Methods which are the actions the object can take. 4:00 This object only needs to do one thing, get a random fact. 4:10 Let's define a method for it. 4:15 We'll call it get fact, and 4:16 it will return a string, which will be the randomly chosen fact. 4:18 Right after our methods comment, let's type public String getFact, 4:21 with open and closing parenthesis, an open curly bracket, and hit Enter. 4:28 Now we just need to make this method return a random fact. 4:34 Let's cut and paste some code from our activity class into our getFact method. 4:37 This is the refactoring part. 4:42 Over in FunFactsActivity, and let me hide the project pane, 4:44 select everything here in the onClick method, except for 4:50 the last two lines where we're actually setting the text. 4:54 Since setting the text is part of how the screen looks, 4:59 it should stay as a responsibility of our activity class. 5:02 Then let's cut the text with Cmd or Ctrl+X. 5:06 Let's leave this error for now and go back to our FactBook class and 5:10 paste in the code. 5:14 We didn't copy over any of our imports. 5:16 So hit OK to let Android Studio automatically create the ones we need. 5:19 GetFact now gets a random element from the facts array. 5:25 But we still need to return which fact was selected. 5:29 So instead of setting up a fact variable with a random fact, 5:32 let's just return the random fact. 5:36 Nice, we've just made a new FactBook class and 5:42 given it a method which will return a random fact. 5:45 Let's take a short break, and then we'll see how to use our method and 5:49 fun facts activity. 5:53