Introducing Maps3:56 with Ben Deitch
In this video we'll learn what Maps are and create our own Map!
Hi, I'm Ben, and in this course we're going to learn about maps. 0:09 In Java a map is a data type that lets us store key value pairs. 0:13 You may not know it, 0:18 we've already been using key value pairs with lists and arrays. 0:19 Let's say we have a list that looks like this. 0:24 It has Waffles at Index 0, Gyros at Index 1, and Enchiladas at Index 2. 0:27 Another way to look at this would be as a mapping of keys to values. 0:33 So with a list or an array the keys are always going to be the same. 0:38 We'll start with zero and start counting upwards. 0:42 But sometimes we need a little more flexibility with what we use as keys, 0:46 this is where maps come in. 0:50 With a map instead of being integers, our keys can be any type we'd like. 0:52 Which means when you create a map you not only need to specify a type for 0:58 the values, but you also need to specify a type for the keys. 1:02 It also means that we can turn this list into something a lot more meaningful. 1:06 By using a map instead we're able to associate each of these foods with 1:11 a meal instead of just some arbitrary number. 1:15 Now that we've got a better idea of what a map is, 1:19 let's jump into some code and try to make this map. 1:21 Let's create a new project. 1:24 Click through the screens. 1:28 And name the project Maps. 1:32 Once we've got the project, let's delete the comment. 1:35 And instead let's create a new map variable. 1:40 And notice that it's an interface that takes in two type parameters. 1:45 One for the key and one for the value. 1:51 Let's hit Enter to import it. 1:53 Then let's add the angle brackets and 1:57 declare our keys to be strings and our values to also be strings. 2:00 Then let's name our map meals and add the equals sign. 2:05 Now, remember, 2:11 since map is an interface we won't be able to use it to create a new map object. 2:12 Instead we'll need to use a class that implements the map interface. 2:17 It's just like what we had to do with our lists except instead of using list and 2:22 array list here we'll be using map and HashMap. 2:28 So let's set this equal to a new HashMap, and use Enter to let it 2:32 auto complete, then add the semi colon, and we're good to go. 2:36 Now that we've got our map we just need to add our three meals to it. 2:41 To add an entry to a map we use the put function. 2:46 So on the next line let's add our breakfast to 2:49 the map with meals.put and pass in breakfast for 2:54 the key and Waffles for the value. 3:00 Nice. 3:04 Then let's do the same thing for our lunch and our dinner. 3:05 So meals.put and lunch will be Gyros. 3:09 And meals.put and let's make dinner at 3:19 our Enchiladas Great, 3:24 let's finish up by printing out what's on our map to make sure everything's working. 3:28 So System.out and pass in meals and then let's run it 3:33 Perfect, that's exactly what we put in there. 3:43 But there's still more to learn about maps. 3:46 In the next video will see how to pull items back out of the map and 3:49 see what else the map interface has to offer 3:53
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