7- The List Interface

Jun 21, 2026 09:43 · 3:51 · English · Whisper Turbo · 2 Locutores

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The list interface represents an ordered collection,

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also called a sequence.

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So with lists,

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we can access objects by their index.

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In collections,

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we don't care about the index of objects.

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We just care about adding or removing them from a collection.

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So in your applications,

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if you want to work with an ordered collection,

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if you care about the index of objects in a collection,

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you should use the list interface.

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So let's declare a variable of type list of

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string.

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we're going to import this,

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and set it to a new array list.

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Now because the list interface extends the collection interface,

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here we have all the methods you learned about in the last video.

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So we can call list .add to add a few items,

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B, and C,

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but we also have an overload of the add that takes

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an integer.

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So if you want to insert a value or an object at a particular index,

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we use this overload.

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Let's say I want to add

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an exclamation mark at the beginning.

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So you pass 0 as the index of the first item.

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Now we can print the list and here's

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the result.

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We couldn't do this with the collection interface because collections don't support indexing.

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Now we can also add multiple items in one go.

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So here we call collections that

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add all.

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Now look at the first parameter.

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It's a collection.

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So because every list is a collection

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Here we can pass our list object along with a few values

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like a,

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b, and c.

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Here we can get an object by its index using

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the get method.

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So we can get the first item and print it and we get a.

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We also have a method for replacing an object at the given index.

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So list .set.

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Let's set the first object to a plus.

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Now we print the entire list and here's

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the result.

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We can also remove an object by its index.

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Here we call list .remove 0.

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Again,

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we didn't have this method in the collection interface because collections don't support indexing.

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Now take a look.

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A is gone and we only have B and C.

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Another useful method is the

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index of method.

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So we can call the index of method and pass A and

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this will return the index of the first occurrence of A.

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In this case,

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it's going to be 0.

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Now, if you search for a value or an object that doesn't exist here,

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you're going to get negative 1.

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There you go.

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Another useful method is last

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index of,

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and this will return the index of the last occurrence of this object.

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So if you add another a here,

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the index of the second a is going to be 3.

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So,

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there you go.

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Now I'm going to remove this.

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Another useful method is the sublist method.

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So we can call list .sublist.

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Here we pass two indexes,

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from and to.

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From is inclusive,

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but to is exclusive.

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So we can start from index 0 and get all the items up

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to index 2.

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And this will return the objects at index 0 and

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1. Take a look.

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There you go.

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Just realize that the original list is not affected because this

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method returns a new list,

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okay?

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So this is all about the list interface.

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Next we're going to talk about sorting data.

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