Casting Instances

We just saw how we can group together different objects 0:00 by using an array with a common base class. 0:03 Now let's see how to use a cast so we can call makeSound on our dog object. 0:06 First, since we got rid of our dog variable, let's make a new one. 0:11 Let's add a new line after our object array and type dog. 0:16 And we'll name it dog, and set it equal to the first item in our array. 0:20 So list at position 0, which gives us an incompatible types error. 0:25 This is where the cast comes in. 0:33 A cast, or type casting, is when you tell Java that an object 0:36 is a more specific descendant of that object. 0:40 Essentially moving the object up its family tree. 0:44 For example, if we were storing a car as a vehicle object and 0:48 needed to turn it back to a car object, we would use a cast. 0:53 To use a cast, you just write the name of the class between parentheses. 0:57 So right after the equal sign, 1:02 let's add a cast to change list 0 to a dog object. 1:05 So parenthesis and inside them we write the class, Dog. 1:10 Nice, it doesn't look like we have any errors. 1:15 And if we run it, We get the right output. 1:19 But before we move on, 1:26 let's see what happens if we try to merge these two lines. 1:27 Let's hide the run panel, and then delete line seven, 1:31 and change dog to list at position zero. 1:39 Then let's add the cast, and it doesn't work. 1:45 It turns out that the call to makeSound happens before the cast. 1:50 So to make sure that the cast happens first, 1:56 we just need to use some parentheses. 2:02 Okay, we've got an array of objects and 2:08 seen how we can use casts to move an object up its family tree. 2:11 But this only works because we know exactly where our dog is in the array. 2:15 If we accidentally tried to cast our dog food object to a dog, 2:21 we'd crash the program. 2:25 And just to make sure, Yep, we get a class cast exception. 2:27 Cmd or Ctrl+Z to undo, and we're back to working code. 2:38 So instead of just picking out the dog object, 2:43 let's loop through our list array and only call makeSound if the object 2:46 actually has a makeSound method, meaning the object is an animal. 2:51 Let's delete line 7 again, and let's use a for each loop to loop through our array. 2:56 For object, we'll call it object, and, 3:04 which is represented by a colon, 3:09 our list array, and add the brackets. 3:13 And inside the for loop, we need to determine if this object is an animal. 3:17 Luckily, there's a keyword for this. 3:22 Let's write an if statement. 3:24 And for the condition, let's check that object, instance of. 3:28 Animal. 3:36 And notice that instanceof is all one word and all lowercase. 3:37 Using the instanceof operator allows us to check if one object 3:44 is an instance of another. 3:49 So inside the if statement, 3:51 after we add our brackets, object is guaranteed to be an animal. 3:54 However, even though it's guaranteed to be an animal, we'll still need to cast it. 4:00 Let's type object., and choose makeSound 4:06 to have IntelliJ automatically add the cast and call the method. 4:10 Awesome, now let's run the app. 4:16 And perfect, we're still getting the same output. 4:21 Using casts and the instance of operator 4:25 gives us a lot more freedom with how we handle our objects. 4:28 Why don't you get a little more practice, and 4:31 in the next video, we'll take a deeper look at the object class. 4:34