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Super Override6:25 with Ben Deitch
In this video we'll learn what it means to 'override' a method and see how to use the 'super' keyword.
We just finished talking about a few methods that are available to 0:00 every object, but 0:04 we got a little confused when the toString method said that it should be overwritten. 0:05 In Java an override is when a child class has a method with the exact same 0:10 signature as one in the parent class, but with a different implementation. 0:15 It's like saying yes, I do have this method, 0:20 but I'd like to handle it differently than my parent does. 0:23 Think about all the things you do differently than your parents, 0:27 that's overriding. 0:31 Let's get more familiar with overrides by overriding the toString method in 0:32 our animal class. 0:37 Let's close object.java, and back in our animal class, let's make a new 0:38 toString method with the same signature as the one from the object class. 0:44 So it should be public return a string, 0:51 be named toString, and not have any parameters. 0:54 Then let's add a method body and inside, 0:59 let's return what type of animal this is and what sound it makes. 1:02 Let's type return and then to get the name of the animal, 1:07 let's use the getClass method, and then call .getSimpleName 1:12 which returns the class name without the package. 1:17 Then let's add a + and in quotes, let's add a ": sound = 1:21 "and then we'll just add our sound variable, and a semi-colon. 1:27 Then let's run the app, And now, instead of getting 1:34 the nonsense we got before, we get something useful, awesome. 1:39 However, we're not done yet, there's still one thing missing, and 1:44 that's the @Override annotation. 1:48 Let's add a line above our toString method, and type @Override. 1:51 Annotations like these aren't strictly required, but you should always do it. 1:58 It lets Java know that we're attempting to override an already existing method. 2:03 So if we change the name of the method to, getString, 2:08 it'll let us know that the method does not override one from its superclass. 2:16 We'll learn more about annotations later. 2:24 But for now, just know that when you override a method, 2:26 you should add an @Override annotation. 2:30 Okay, let's change that back to toString. 2:32 And then, I want to show you another way we could have done this. 2:36 Let's copy our return line, And then delete this whole method. 2:40 And I'll hide the run pane as well. 2:46 Then, let's use Ctrl + O to open the override menu. 2:53 And let's arrow down to the toString method and accept it. 2:57 Then let's paste in our return line, and we're done. 3:01 Intellij has tons of little shortcuts like this, and 3:05 while I'll do my best to show them off, that doesn't mean you have to use them. 3:08 There's nothing wrong with just typing it out. 3:14 Though did you see what it defaulted to for the return? 3:16 Let's use Cmd or Ctrl + Z to undo and take another look at this. 3:20 It looks like it's returning super.toString. 3:26 In Java, the super keyword refers to the parent class, 3:30 meaning this is calling the toString method of the object class. 3:34 Okay, let's redo our paste, And 3:40 then let's see why we need the super keyword. 3:44 Let's say that every time a dog makes sound, it should also wag its tail. 3:49 To do this, we'll need to override the makeSound method and our Dog class. 3:55 Let's add a line at the bottom of the Dog class, and 4:00 use Ctrl + O to override the makeSound method. 4:04 Then let's a line after the call to super, and 4:08 type sout, And in quotes, let say *wags tail*. 4:13 And now, when we call the makeSound method on a Dog object, 4:20 it'll first call animals make sound method and then print out wags tail. 4:23 Let's try it up in the main method. 4:29 Let's delete line 7 again, And 4:33 then call dog.makeSound. 4:37 And if we run it, Perfect, that's just what we were expecting. 4:41 Another place you might see the super key word is in a constructor. 4:47 Let's see how that works by making sure that every animal has a sound, 4:50 by requiring it and the constructor. 4:55 Let's start by adding a constructor to the animal class and 4:57 making sure it takes on a string perimeter. 5:01 So Animal, and in parenthesis, it'll take in a string variable called sound. 5:06 Then let's add the brackets, and we've got our constructor. 5:13 Inside the constructor, 5:16 let's update our sound field to equal the new sound parameter. 5:18 this.sound = sound, nice, but 5:22 now we're getting an error in our Dog class. 5:27 Since an animal now requires a sound in its constructor, we 5:32 need to call through to that constructor in order to have a valid animal. 5:37 To do that, you just use the super key word followed directly by parentheses. 5:41 So instead of setting the sound equal to bark, 5:47 we want to call the constructor in the animal class by using 5:51 the super key word and passing in bark for the sound. 5:55 Let's run it one more time and make sure it still works. 6:00 Awesome, being able to use overrides and 6:08 the super keyword can really help turbocharge your programming, and 6:11 give you a lot more options for how to build an app. 6:16 Though giving developers more options isn't always a good thing. 6:19 More on that in the next video. 6:23
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